# Stihl MS880 runs at high idle then dies.



## chad556 (Feb 26, 2011)

Ok so today I went out to pursue a great find on CL, a nice ms 880 for $650 (I was set on finding a 660 for that price). The guy said the reason for the low price was that the saw would start but would not idle, it would just rev up to half throttle, sputter and then quit, I figured simple enough just a little tweaking and I could get it running strong again, probably a carb issue. Well, the whole story was that he took it to his local stihl dealer and they told him that the piston and clyinder were bad, causing the saw to rev up fast when it was started instead of idle like it should. This seemed kind of strange to me, the saw obviously has decent compression (nearly ripped my fingers off trying to start it) The dealer told the guy $700 to replace the piston and cylinder to get the saw running again.

Probably against my better judgement I shelled out the cash anyways and took the saw home. Cleaned it up, cleaned the carb and started experimenting with the High Low and Idle screws. No luck, the longest i got it running was about 20 seconds and it wildly revs up and down, It wont go down to idle when i take the trigger off and when i go to full throttle the saw only goes up to ~1/2 to 3/4 throttle at best and then "pulses" (sounds like somethings going to break.) I don't have a bar and chain for it, all of mine are 3/8" and dont fit on the bar studs. I am getting a 36" carlton one from baileys. Is there anything about this that seems wrong to any of you? (I admit I am a novice when it comes to tinkering with chainsaws) Could it really be the piston and clyinder are bad? I wouldnt think it would fire at all if that were the case? Im stumped and I dont want to spend more money or make a bigger mess than i have to, can anyone give me a place to start or point me in the right direction?


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## mdavlee (Feb 26, 2011)

Check the fuel filter and tank for crud. Did you clean the screen in the carb? Was it full of junk? Have you peeked in the spark plug hole at the cylinder walls?


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## THALL10326 (Feb 26, 2011)

chad556 said:


> Ok so today I went out to pursue a great find on CL, a nice ms 880 for $650 (I was set on finding a 660 for that price). The guy said the reason for the low price was that the saw would start but would not idle, it would just rev up to half throttle, sputter and then quit, I figured simple enough just a little tweaking and I could get it running strong again, probably a carb issue. Well, the whole story was that he took it to his local stihl dealer and they told him that the piston and clyinder were bad, causing the saw to rev up fast when it was started instead of idle like it should. This seemed kind of strange to me, the saw obviously has decent compression (nearly ripped my fingers off trying to start it) The dealer told the guy $700 to replace the piston and cylinder to get the saw running again.
> 
> Probably against my better judgement I shelled out the cash anyways and took the saw home. Cleaned it up, cleaned the carb and started experimenting with the High Low and Idle screws. No luck, the longest i got it running was about 20 seconds and it wildly revs up and down, It wont go down to idle when i take the trigger off and when i go to full throttle the saw only goes up to ~1/2 to 3/4 throttle at best and then "pulses" (sounds like somethings going to break.) I don't have a bar and chain for it, all of mine are 3/8" and dont fit on the bar studs. I am getting a 36" carlton one from baileys. Is there anything about this that seems wrong to any of you? (I admit I am a novice when it comes to tinkering with chainsaws) Could it really be the piston and clyinder are bad? I wouldnt think it would fire at all if that were the case? Im stumped and I dont want to spend more money or make a bigger mess than i have to, can anyone give me a place to start or point me in the right direction?



Easy way to find out, remove the muffler and have a look, a 10 minute job. If it has gobbs of compression that doesn't fit a scored cylinder deal so have a look, easy job...


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## mikefunaro (Feb 26, 2011)

Take the muffler off and look in through there or get a flash light and look in through the plug hole and see if you can figure out what's up. 

The fact that it's kinda sorta running a little bit means that things might not be completely trashed and you will have to look closely. 

Not to beat up on you, but when you suspect that the P&C are toast on a saw, it's good measure to deduct that from the used price of the saw. the fact that he told you a dealer said this should reaffirm any worries you already have. 

You will do OK here and will not get totally screwed even if you have to replace both at OEM price, given that the cost of the saw is $1600+ new. 

Unfortunately, if the cylinder and piston are bad, you have to find out what caused them to go bad, and on a saw like an 880, its unlikely that it will be a noob mistake of straight gasing. There is probably an air leak somewhere. 

You say NYC--are you north of NYC? What golf course? St. Andrews? Those saws were up in Carmel right? 

I'll be down there mid march on vacation (my parents live in Hastings) so I'll take a look and see if we can figure it out if you havent sorted it out by then. 

Unfortunately the labor rates at most NYC area stihl dealers are through the roof so this is one where you'll save a lot of $$ if you can take care of this yourself.


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## rob066 (Feb 26, 2011)

Check fuel line for holes or cracks. Also check impulse line. Like said before check cylinder condition


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## chad556 (Feb 26, 2011)

Thanks for the advice guys. I will check all this stuff when I get it back into the shop tomorrow. Our mechanic is on vacation for the week but when hes back im sure he could probably help too. If i can i will try to maybe post videos or pics. I have seen/taken apart a couple pistons and clyinders but i havent really seen much of what scoring looks like first hand. I'll keep you posted what I find out.


PS. yep it was the saw from Carmel NY and I'm all the way down in Staten island. It was too long a drive to come back empty handed and even if I have to put a couple hundred in it to get it going its still a hard deal to beat.


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## mikefunaro (Feb 26, 2011)

chad556 said:


> Thanks for the advice guys. I will check all this stuff when I get it back into the shop tomorrow. Our mechanic is on vacation for the week but when hes back im sure he could probably help too. If i can i will try to maybe post videos or pics. I have seen/taken apart a couple pistons and clyinders but i havent really seen much of what scoring looks like first hand. I'll keep you posted what I find out.
> 
> 
> PS. yep it was the saw from Carmel NY and I'm all the way down in Staten island. It was too long a drive to come back empty handed and even if I have to put a couple hundred in it to get it going its still a hard deal to beat.


 
Yeah I understand then...especially with all the ####ing bridge tolls...ruining the savings of my craigslist transactions...


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## pioneerguy600 (Feb 26, 2011)

This could be caused by a combination of things. #1, check to see if the throttle is closing completely.
#2 check all the fuel lines for cracks 
#3 carb may need to be pulled and cleaned up but high revving at idle sounds like an air leak so a vac test is always the best path to diagnose air leaks.
Pioneerguy600


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## mikefunaro (Feb 26, 2011)

Off topic but did you know mike sorrentino before he got big?


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## chad556 (Feb 26, 2011)

Haha yeah between the tolls and the gas thats like 50 bucks extra right there.

Well I took the carb apart and found something interesting: the fuel line that goes to the top of the carb (the part with that gold little filter and stuff and the metal L shaped fitting, sorry I don't know the terminology) was obstructing the throttle motion. the throttle was sometimes getting hung up on the fuel hose and had to be pumped a little before it would release. I rerouted the hose where it doesnt get bumped and put it back together, I dont know if this will solve the problem, i dont think it will, but i cant test it out again until tomorrow, my girlfriend is already pissed the apartment smells like gas lol. I also got a peek at the piston and like I said, im no expert but it looks pretty good to me. No obvious burns or gouges. I can even see one of the rings and it looks fine to me as well. Check out my pictures and let me know if anything looks fishy.


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## chad556 (Feb 26, 2011)

mikefunaro said:


> Off topic but did you know mike sorrentino before he got big?


 
The jersey shore guy? Haha, no but then again I've only been down here for a year I'm originally from upstate


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## jimdad07 (Feb 26, 2011)

chad556 said:


> The jersey shore guy? Haha, no but then again I've only been down here for a year I'm originally from upstate


 
Sounds like and air leak, you could always try pressurizing the crank case and use soap bubbles on the oil seals to see if those are leaking if the fuel line and impulse line checks out.


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## chad556 (Feb 27, 2011)

Uh oh, I took the saw apart today and here is what i found:





















I have a video of it running that I will post as soon as it uploads, it was taken right after I put everything back together.

As I have said i'm not that experienced with this stuff but how bad does that piston and cylinder look? do i need a whole new top end or could i get away with just a new piston and rings and smooth out the cylinder with a hone or something?

Also, what is the best way to do a compression test I have a little 3gal 100psi air compressor and a bike pump to work with. Do i need any specialized tools? Sorry my search for answers isn't going well because of my lack of nomenclature i think.

Thanks in advance for all the help and advice, i'm feeling more and more foolish about this whole experience but im having fun figuring each little thing out. I guess thats how you learn right?


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## chad556 (Feb 27, 2011)

[video=youtube;2n59Jj849b4]http://www.youtube.com/watch?v=2n59Jj849b4[/video]

Maybe this will help you guys advise me on what to do next. The top end is far from perfect shape but if it runs like this could it be salvageable?


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## mikefunaro (Feb 27, 2011)

Compression test is different from a pressure vac test. A pressure vac test will check the case for leaks, the "compression" test will test the compression achieved by the piston and cylinder. Now that you can see the actual damage, the results of the P&C compression test arent too relevant. 

If I were you I would refrain from running the saw in its current state beyond what you did for that video as if their is a leak or something you're not going to make things any better (and probably will make things worse) in running the saw. 

Someone will follow with links on how to do an at home vac test. DO NOT go at the cylinder with a flex hone until you get the rest of it sorted out. If you do, just a few seconds. Don't think of the hone as a way to burnish away the problems though. You will trash the cylinder. You may be able to do some light sanding and or an acid treatment. Links will most likely follow to this as well. 

My guess from the photos is that the piston needs to go.


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## chad556 (Feb 27, 2011)

Ok, so $35 on ebay for a new 60mm piston kit and cross my fingers that i can salvage the cylinder. But before all that I will figure out how to do a pressure and vac test to diagnose and correct possible air leak problem? No more running the saw or taking a hone to it until i know what the problem is and fix it. If the cylinder does need to be honed a little though (or replaced) how will i know? should i try it without touching the cylinder first or could that kill the new piston i put in it? Haha im getting nervous here.


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## pioneerguy600 (Feb 27, 2011)

The comp is low on that saw and the sound of it running tells its running lean.Don`t run it any more in that condition. There is a reason that piston is scored up that way, you need to find out what caused it, my bet is an air leak. That is what needs to be done before you tear it apart, do a vac test or go straight to a low air pressure test and find the source of the leak. You can waste a lot of time chasing an air leak by just pulling parts off but a low pressure air supply hooked to a properly blocked off engine will show up the air leak or leaks by just spraying all known leak areas with soapy water.
Pioneerguy600


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## mikefunaro (Feb 27, 2011)

chad556 said:


> Ok, so $35 on ebay for a new 60mm piston kit and cross my fingers that i can salvage the cylinder. But before all that I will figure out how to do a pressure and vac test to diagnose and correct possible air leak problem? No more running the saw or taking a hone to it until i know what the problem is and fix it. If the cylinder does need to be honed a little though (or replaced) how will i know? should i try it without touching the cylinder first or could that kill the new piston i put in it? Haha im getting nervous here.


 
There are lots of threads on cylinder salvage here using different kinds of acids or mild abrasives. You should search. The hone is to restore a slight cross hatched pattern to the cylinder to improve compression, it is not to "buff out" the problem areas or damaged areas.


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## josh1981 (Feb 27, 2011)

first question is are you in tree cutting business? 

replace p/c, fuel line, fuel filter at very least. 

how did the neighbors like the saw running in apt? lol


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## shawn022 (Feb 28, 2011)

In post #10, the picture of the carb you can see the remains of the black gasket on the top cover. Was the gasket there when you tore down the carb? If not you could be sucking air just like a bad impulse hose would. Definatley read up pressure and vac testing.


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## chad556 (Mar 2, 2011)

josh1981 said:


> first question is are you in tree cutting business?
> 
> replace p/c, fuel line, fuel filter at very least.
> 
> how did the neighbors like the saw running in apt? lol


 
Haha, Actually I'm in the golf course business which means I only cut trees when theres no grass to cut. Actually this year we took out some big oaks and other species and i want to try my hand at milling so I'm trying to get that 880 running.

Oh, and my neighbors probably think im crazy, not everyday you see a guy trying to start up a 120cc saw, especially in a neighborhood where the tallest tree in sight is a 15' callary pear


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## chad556 (Mar 3, 2011)

shawn022 said:


> In post #10, the picture of the carb you can see the remains of the black gasket on the top cover. Was the gasket there when you tore down the carb? If not you could be sucking air just like a bad impulse hose would. Definatley read up pressure and vac testing.


 
Good eye, didnt even notice that, it sure looks like there should be a gasket there. I certainly didn't lose it, must not have been there. So I need a carb rebuild kit too? Any ideas where to find one? also, I'm having a hard time finding a good instructional pressure/vac test video/picture thread so if anyone can point me in the right direction i would appreciate it.


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## josh1981 (Mar 3, 2011)

chad556 said:


> Haha, Actually I'm in the golf course business which means I only cut trees when theres no grass to cut. Actually this year we took out some big oaks and other species and i want to try my hand at milling so I'm trying to get that 880 running.
> 
> Oh, and my neighbors probably think im crazy, not everyday you see a guy trying to start up a 120cc saw, especially in a neighborhood where the tallest tree in sight is a 15' callary pear


 
Do you do it by yourself? if so how did you get started? Golf course? lawn maint?

Well I live in a townhome my neighbor had a small craftsman saw. Actually most people in my area only use small homeowner HD saws or small stihl... And I have a 066 361 211 yes my neighbors think im crazy... but I cut firewood in winter. and storms around here can get rerally bad. $$$$ if big tree falls!

Oh I saw that staten island storm on youtube last year I think? Mayor was on there and showed one guy cutting with a stihl saw. Hope everyone was ok in that.

About your saw how is the carb and is muffler screen plugged up?


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## mtngun (Mar 3, 2011)

chad556 said:


> Good eye, didnt even notice that, it sure looks like there should be a gasket there. I certainly didn't lose it, must not have been there. So I need a carb rebuild kit too? Any ideas where to find one? also, I'm having a hard time finding a good instructional pressure/vac test video/picture thread so if anyone can point me in the right direction i would appreciate it.


 Carb kit is always good insurance and they don't cost much. You can either order it from a Stihl dealer, or, once you determine the kit # by looking up the carb info on the carb manufacturer's website, you can get it on the 'bay or from an AS sponsor like Bailey's.

Here's one thread on vacuum testing. Pressure testing works the same way except you need a pressure source -- only a few psi so as not to damage anything. If it passes the vac test, you're probably good to go. If it flunks the vac test, a pressure test can help pinpoint the leak. Some people like to do both tests just to be safe.

http://www.arboristsite.com/chainsaw/42768.htm


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## chad556 (Mar 4, 2011)

josh1981 said:


> Do you do it by yourself? if so how did you get started? Golf course? lawn maint?
> 
> Well I live in a townhome my neighbor had a small craftsman saw. Actually most people in my area only use small homeowner HD saws or small stihl... And I have a 066 361 211 yes my neighbors think im crazy... but I cut firewood in winter. and storms around here can get rerally bad. $$$$ if big tree falls!
> 
> ...


 
No, nothing quite as fancy as that, I have a bachelors degree in golf course management and I work as an assistant superintendent at a private club.

Oh and I think I remember that strom, it was the first week I moved down to SI about a year ago, huge mess, lots of lost power, blow downs, flooding. It made for an interesting first couple weeks on the golf course. Lots of raking.

As for the saw I think I am going to find out what I need and rebuild the carb just to be safe, as far as the muffler screen, I took it out and will probably leave it out unless there is a really good reason to have one?

Also thanks for the link to the Vac test tutorial mtngun. Seems like every time i search for something i find tons of interesting threads but not the one i need lol. I am going to harbor freight tomorrow to pick up that break bleeder kit and see if i can do a vac test. My piston kit came in the mail so thats all ready to go. My muriatic acid is coming soon so i can clean up the cylinder. Thats a lot of crap to buy but its way cheaper than going to the dealer, plus i'm getting the invaluable experience.

One more question: If i do the pressure test I need the flywheel and clutch removed so i can test the crank seals, correct? are there any other areas I should test or that i would need to access? Thanks


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## Andyshine77 (Mar 4, 2011)

Check the crank seals, cylinder base gasket, carb intake boot, impulse line and fuel line. That's all I can think of at this hour. 

First determine that you do have an air leak with a pressure and vacuum test. If you do in fact have an air leak, yes remove the flywheel and clutch then spray down everything with soapy water. With the case under pressure any leak will produce lots of bubbles.


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## chad556 (Mar 4, 2011)

*More pictures*

Ok so I got my vac tester today and did my best to use bike tubing to seal the case. I kept having no luck with the muffler because it clamps on and its not designed to have a gasket so I made a piece of rubber for the outlet of the muffler (formerly where the spark arrester screen was) and that worked out ok I think. I pumped it up and no matter how fast I pumped I couldnt get it past 5 inHg on the gauge. Not sure where the leak was but strongly suspecting the gasketless muffler I tried to do a pressure test. In the process of removing the clutch and the flywheel I got my little rope jammed into the exhaust port. Long story short, I had to remove the cylinder so I decided to take the whole thing apart and take a look at what was going on. Here is what i found:



























How does this look to you guys? Is it worth trying to salvage the cylinder? It doesnt look so bad to me but then again this is my first time really getting my hands dirty with this stuff.

Also I still have not gotten my flywheel off, I'm going to just keep tapping away at it but if anyone can give me a better way i would love to hear it.


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## mtngun (Mar 4, 2011)

Thanks for the great pics.

I have never seen anything quite like it, so I'm hoping someone else will chime in.

That almost looks like a crack running between the exhaust port and the upper transfer ? Weird, anyway.





It's great to take the jug off to see the damage, but now you can't leak test it, and you still do need to leak test it. Dunno what to tell you about the 880's unique muffler attachment. If it's not holding vacuum, the next step is to apply a few psi pressure (easier said than done, you'll need a source of of low pressure air) and find out where it is leaking. Should be able to hear it hiss and/or spray soapy water and look for bubbles.


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## mtngun (Mar 4, 2011)

Regarding flywheel removal, a special puller is required, don't try to hammer or pry it off or you'll end up breaking it.


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## RiverRat2 (Mar 4, 2011)

Just looking I think You cylinder is going to be fine,,, Can you hang a finger nail in any of the grooves or aluminum deposits??? You will Know better after you remove the aluminum transfer,,, Ive got an 066 that I put a Meteor piston in 3 years ago that looked worst than that,,, it makes 165 psi. compression and is bad to the bone!!!! Make sure the impulse hose is in good shape... It sounds like an air leak to me from your description and watching the vid,,,

Good luck!!!


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## chad556 (Mar 4, 2011)

There is a little bit of a fingernail hang up on some of the rougher spots. I am hoping that that turns out to be mostly aluminum from the piston but I wont know for sure until I clean it up with my acid (once it gets here). All I can do now is wait until i get the acid (i'll be sure to post an 'after' pic), then clean up the cylinder, install my new piston, pop off my flywheel and pressure test my seals and gaskets, rebuild the carb, then put it all back together, slap on the new bar and let her rip.

I have a pretty good assortment of pullers and related tools at my disposal at work to get that flywheel off (im not going to bang on it anymore than i have, the thing is plastic after all), also our mechanic is going to be back from his vacation so hopefully he will help me figure it all out on Monday. Thanks for all the help and advice so far and don't worry, I will keep you posted on my progress of getting this beast running again.


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## mtngun (Mar 5, 2011)

chad556 said:


> I have a pretty good assortment of pullers and related tools at my disposal at work to get that flywheel off (im not going to bang on it anymore than i have, the thing is plastic after all), also our mechanic is going to be back from his vacation so hopefully he will help me figure it all out on Monday.


It requires a threaded puller. You can either get it from Stihl, or get a generic one that is used for mopeds. Can't remember the thread sizes off the top of my head.

In any event, you don't need to pull the flywheel to do a vac test, only if you suspect a leak on the flywheel side seal. Figure out a way to seal the muffler, bolt the jug back on (no need to install rings, etc) and figure out where the leak is.


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## josh1981 (Mar 5, 2011)

thats cool. good money. 

leave the spark screen in there. its there to prevent sparks from flying out causing fires. could get ion major trouble.

good luck on rebuild.




chad556 said:


> No, nothing quite as fancy as that, I have a bachelors degree in golf course management and I work as an assistant superintendent at a private club.
> 
> Oh and I think I remember that strom, it was the first week I moved down to SI about a year ago, huge mess, lots of lost power, blow downs, flooding. It made for an interesting first couple weeks on the golf course. Lots of raking.
> 
> ...


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## chad556 (Mar 5, 2011)

Ok so I put my jug back on this morning and tried to seal up the muffler again, I found out there is a muffler gasket it was just stuck to the cylinder. I had a hard time getting the muffler to seal but i finally got a piece of inner tube in there and did a vac test, i pumped the gauge up to 5 in-Hg and about 15 minutes later it has only dropped about a quarter of an in-Hg on the gauge. This would be passing correct? Im not too sure where to go from here but i guess i just proceed with the rebuild? what other ways can a piston get scored like that? Bad carb adjustment, hard use, straight gas/bad mix? I think I can rule out air leak.


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## splitpost (Mar 5, 2011)

chad556 said:


> Ok so I put my jug back on this morning and tried to seal up the muffler again, I found out there is a muffler gasket it was just stuck to the cylinder. I had a hard time getting the muffler to seal but i finally got a piece of inner tube in there and did a vac test, i pumped the gauge up to 5 in-Hg and about 15 minutes later it has only dropped about a quarter of an in-Hg on the gauge. This would be passing correct? Im not too sure where to go from here but i guess i just proceed with the rebuild? what other ways can a piston get scored like that? Bad carb adjustment, hard use, straight gas/bad mix? I think I can rule out air leak.


 
sometimes a vac test won't pic up a leak ,thats when you need to do a pressure test to be sure


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## mtngun (Mar 5, 2011)

Your vac test sounds good. 

There's still the fuel line, fuel filter, and carb to investigate.

I still haven't figured out the unusual wear pattern on the jug. :msp_confused: I'm hoping someone will come along and say "hey, I've seen something like that before and here's what caused it."


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## chad556 (Mar 6, 2011)

splitpost said:


> sometimes a vac test won't pic up a leak ,thats when you need to do a pressure test to be sure


 
I'm a step ahead of you there, before I took all the seals i made out I put about 10 lbs of pressure in there and sprayed the thing down repeatedly with soapy water. It held the pressure and the only bubbles I got were a couple coming from the muffler where my little inner tube couldnt hold on. No other bubbles or tell tale hisses

Also mtngun, Thanks for the advice im going to remove the impulse and fuel lines just to get a good look at them and replace if necessary. After hunting endlessly for a carb kit i found one for an 084 carby that looks like it will have most of what I need, some of the gaskets on my carb look iffy (stiff and crumbly) so I'm going to rebuild it and see. From everything I have seen so far I think the carb is the best candidate for the saw running lean. I am guessing the carb started to fail and the previous owner just kept running it, hence the damage. Sounds like a reasonable cause and effect right? I mean, it could have happened that way right?

Anyway, just waiting on my acid on monday to clean up the cylinder and then my bar chain and carb kit will come at the end of next week, get all that together and I think I will be good to go.


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## CTYank (Mar 6, 2011)

chad556 said:


> Ok so I put my jug back on this morning and tried to seal up the muffler again, I found out there is a muffler gasket it was just stuck to the cylinder. I had a hard time getting the muffler to seal but i finally got a piece of inner tube in there and did a vac test, i pumped the gauge up to 5 in-Hg and about 15 minutes later it has only dropped about a quarter of an in-Hg on the gauge. This would be passing correct? Im not too sure where to go from here but i guess i just proceed with the rebuild? what other ways can a piston get scored like that? Bad carb adjustment, hard use, straight gas/bad mix? I think I can rule out air leak.


 
Mind you, I'm no expert in this, but it seems that your test pressure is way low. Reference I have ("Two-Stroke Engine Repair & Maintenance" by Paul Dempsey, McGraw-Hill 2010) recommends drawing down crankcase to 7 psig vac.) 5" Hg would be only about 2 psig. Dempsey further says "If pressure remains constant, or increases by no more than 4.5 psi over 20 seconds, the seals should be okay." (BTW, the book is very helpful in understanding 2-strokes.)

For pressure-testing, his recommended source is 7 psig and no more.

HTH. Regards.


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## RiverRat2 (Mar 6, 2011)

Chad Would you like a copy of the service Manual for an 088??? It should work for your saw and has a detailed description for leakage testing both pressure and vacumn and all the tolerances,,,

What about the IPL for the MS880????It shows the exploded view and has all the part #'s

PM me your Email Addy I would be glad to send them 2 ya

Also On my salvaged 066 I mentioned earlier it looked way worse and cleaned up real good used the muratic acid directly on the aluminum X-fer with a long Q-tip let it work a few mins then use fine emmory to polisih and clean,,, It had a few verticle lines you could see but a fingernal wouldnt hang,,, they will fill in with carbon and actually seal up pretty well.... I used a Silicone Carbide Ball hone to refresh the Cross hatching very lightly and of course ported the cylinder and piston windows and let it rip!!!!!!!!!


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## Andyshine77 (Mar 6, 2011)

If she held pressure like you said it doesn't have a leak. I know a few people that had 088/880's that scuffed the piston and cylinder like yours. I think it's a combination of a few things, not just one big issue, like an air leak. Tuned lean, tight cold bore, bad fuel/oil, then running the saw with a dull ass chain. All of these things will make a new $1,600 880 worth $650 in a hurry.


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## wigglesworth (Mar 6, 2011)

Andyshine77 said:


> ass chain



What exactly is that? Are they hard to file?


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## RiverRat2 (Mar 6, 2011)

Andyshine77 said:


> If she held pressure like you said it doesn't have a leak. I know a few people that had 088/880's that scuffed the piston and cylinder like yours. I think it's a combination of a few things, not just one big issue, like an air leak. Tuned lean, tight cold bore, bad fuel/oil, then running the saw with a dull ass chain. All of these things will make a new $1,600 880 worth $650 in a hurry.



What he said!!!!!


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## gink595 (Mar 6, 2011)

wigglesworth said:


> What exactly is that? Are they hard to file?


 
Sounds Kinky


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## Rounder (Mar 6, 2011)

Andyshine77 said:


> If she held pressure like you said it doesn't have a leak. I know a few people that had 088/880's that scuffed the piston and cylinder like yours. I think it's a combination of a few things, not just one big issue, like an air leak. Tuned lean, tight cold bore, bad fuel/oil, then running the saw with a dull ass chain. All of these things will make a new $1,600 880 worth $650 in a hurry.


 
+2 88's need to be run in the wood, properly adjusted, with a sharp chain. They are a big tough saw....but easy to #### up in the wrong hands.


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## Andyshine77 (Mar 6, 2011)

wigglesworth said:


> What exactly is that? Are they hard to file?


 
Impossible!:msp_lol:


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## rxe (Mar 6, 2011)

Lots of good advice here. 

If pressure and vac test are good, then check fuel delivery. The other thing is that when you tune it, follow a few rules. 

1) If the carb doesn't respond as you would expect, something is wrong. The saw should precisely match what you are doing - so a 1/4 turn in on the H screw = more revs. If not, find out what is wrong, or you'll blow it up. 

2) Creep up on the H setting from below. Have the H screw out two turns. It will blubber up to 6000 rpm. Give it 1/4 of a turn - 7000 rpm. And so on. I've seen people set it up too close, nail the thottle and wind t up to 16K in an instant - result = busted piston.

3) I would tune rich, especially if you are milling. Official spec is 11,500. I'd set it at 10,000 to be really safe.


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## chad556 (Mar 10, 2011)

Ok so update on my situation: I cleaned up the cylinder with the muriatic acid and some very light sanding/polishing, my mechanic friend said it looked great and wouldnt give me any problems. So I installed the piston and put the saw together. I put the carb in(before rebuild) started her up and... same problem, prettymuch exactly what happened in my original video. The next day the carb kit came, so I replaced all my warn out gaskets and parts, reinstalled the carb, started the saw up and... again revved up and died when it should have idled nicely.

I am not sure what to do now. I am 99% sure it is a carburetor issue but i dont know what to do next, I got ahold of a service manual and I'm looking at the exploded view for something that is out of place.

Also I am thinking is there anyway to adjust the H and L screw back to factory settings? I lost that little plastic screw limiting plate so Im not sure what I should do to turn the screws. Im afraid I will damage this thing if I keep doing trial and error. Anyone know a solution to resetting this carburetor? or am i completely on the wrong track here?


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## josh1981 (Mar 11, 2011)

is the spark screen clean? and reajust carb to factiry setings.


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## RiverRat2 (Mar 11, 2011)

View attachment 175761


Look on page 10 your settings are there, if the plate is gone thats OK I suppose have you remoived the red limiter caps,,, thats oK too!!!

Just gently bottom out the screws then back them out to the # of turns listed in the colum with the Limiter caps removed,,, it looks like 1 turn CC from gently bottomed out

Send me a PM if you have any doubts,,,


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## chad556 (Mar 11, 2011)

Ahh cool thanks for the link, I was looking all over for that info. Ok I will play around with it tonight and let you guys know how it goes.

The limiter caps were not on the saw when i got it (possible evidence of why the saw went bad in the first place) so I was a little unsure how to get back to the factory settings, all the carbs i have played around with in the past have only turned around once or 3/4 times or whatever. But hey thats why I asked the experts, thanks guys.

Also, my spark screen is pretty clean. Its sitting in my tool box right now, the saw wont run right with or without it. I will put it back in once I get the saw running before I put it to work though.

One last thing: on the top of my carb there is a fine gold colored screen, a thin, black rubber piece that matches the gold colored screen, and then a rubber gasket that matches the top plate that sits on top of it. I was originally missing the thin rubber piece but it came in the carb kit I ordered so I put it in. The service manual that I found doesn't include either the gold screen or the thin rubber thing. It says only two pieces go in between the top plate and the carb and i have 3 in between them. Does anyone know what I'm talking about? Here is a picture for reference , that is exactly what the carburetor looked like when I took it apart the first time, since then i have added a rubber piece that matches the gold screen piece between the [brand new] gasket and screen.


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## chad556 (Mar 11, 2011)

And one more thing, sorry to go on and on but it might be worth mentioning: When i took the fuel hose out of the carb after getting the saw to run(unsuccessfully) it spewed gas out in a 12" high stream that slowly died down over about 10 seconds, leaving my gas tank almost empty and me partially covered in mixed gas. Is there supposed to be pressure build up in the fuel tank like that? The mechanic I know didnt think it was right but wasn't sure. He said the tank should be vented and shouldnt shoot gas like that. I think hes right but I'm not sure.

Could this be causing the symptoms? Is it even a problem? I'm pretty stumped here there are about 4 things that could possibly be wrong with this thing and I am not sure where to start.


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## mdavlee (Mar 11, 2011)

Did you blow out all the passages in the carb when you had it apart? In that big round hole there's a screen that can be removed and cleaned. Did you remove it and clean it?


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## maico490 (Mar 11, 2011)

Tank building pressure is fine. The vented cap only allows air in. Next time take the cap off before you pull the fuel line but you know that now :msp_wink:


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## RiverRat2 (Mar 12, 2011)

chad556 said:


> Ahh cool thanks for the link, I was looking all over for that info. Ok I will play around with it tonight and let you guys know how it goes.
> 
> The limiter caps were not on the saw when i got it (possible evidence of why the saw went bad in the first place) so I was a little unsure how to get back to the factory settings, all the carbs i have played around with in the past have only turned around once or 3/4 times or whatever. But hey thats why I asked the experts, thanks guys.
> 
> ...



Chad that Gold colored screen is the fuel pump diaphram, It goes against the top side body of the carb, then the gasket then the top cover,,, only two pieces go in between the carb body and the top cover,,,It is very important that they are oriented correctly with regard to the fuel circuits of the carb as well as the gasket,,,,
I have an IPL that shows the exploded view if you would like it,, I think it will help you out alot,,, send me a PM with your Email address & I will send you a copy in PDF FORMAT...


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## chad556 (Mar 12, 2011)

Hey RiverRat i found that same IPL just searching through google looking for more info on this problem. Thanks anyways though. Ok so I returned the carb to factory settings, the L screw was about 2.5 to 3 turns backed out instead of 1 so i was optimistic but when I tried to start it up it had the exact problem.

My next area of investigation was the gas tank vent. The tank builds up a lot of pressure, so much that i have to keep the gas cap off when the carb is off or it will dribble gas all over. I did a little research and decided to take it out and look at it. I also tried to run the saw with out it in. No venting just a half inch hole in the top of the gas tank, and you guessed it, same problem, saw started but took off and stalled when it should have returned to idle. 






I took the vent apart but it looks ok to me just a little dirty. I guess I will rule it out as a problem unless anyone sees something amiss.

Now I am re-rebuilding my carburetor and im putting it under the microscope this time. Here are some pics:





Note the 3 pieces that go between the main carb body and the top plate (i should leave out the middle one correct?)













Right to the right of that little brass colored piece is a corroded/warn area (the other side is just reflection). Looks like something ate away at it somehow, probably not a big deal but then again it could be for all i know.






Not sure how I am supposed to replace this cap, or whats under it or if i should even bother replacing it.






This gasket came with my rebuild kit. Its not in the diagram but I was wondering if there is some place it should go


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## mtngun (Mar 12, 2011)

It's called a welch plug. Yes, you should remove the old plug, clean out underneath, and install the new plug. But first make sure the new plug is the same size -- occasionally you'll get a kit with the wrong size plugs. The new plug is pressed into place and given a lite tap. I doubt the welch plug is your problem, though.





I'm sure you already know this, but just in case, piece #10 usually has a little slot that meshes with the needle valve. 

Gee, it sure sounds like a fuel problem. Too bad you don't have another carb to swap in, just to narrow down the problem.


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## hotshot (Mar 12, 2011)

*One or the other!*

You only use a single fuel pump diaphragm in that carb. I'd choose the black one. The beige colored one is for alcohol fuels & won't pump as much gas. The backer gasket, with open holes & no valves, is used with either one.


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## chad556 (Mar 21, 2011)

Ugh, I still have not been able to get this thing to run.


I pressure and vac tested and could not find any leaks.
I replaced the piston and fixed up the cylinder, tested it to 155 Psi today
Completely rebuilt the carb
Re gapped the coil
New spark plug, new gas new fuel filter, new fuel cap, cleaned gas tank vent
Checked all hoses, muffler, gaskets, air filter.

I put on a 36" brand new bar and chain, the saw starts up and runs, and with a little carb adjustment it revs normally but still will not return to idle no matter how I mess with the carb. I have had the screws in every configuration i could think of from maxed out lean too both at 2.5 turns CCW the saw just wont idle.

Knowing what I have done so far, what would you check next/recheck.


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## josh1981 (Mar 21, 2011)

Hi Chad. I had a similar experience with my stihl blower. New plug carb air filter fuel filter fuel line. Carb adjusted to factory specs. What did I do? Used this:

Strike-hold. Strike-Hold Home Page

Sprayed it on plug. Inside plug hole down to engine. Behind air filter. Inside muffler. Started it up. Exhaust smoke pouring out. cleaned it uP good. Runs like brand new. Actually better then new. 

Maybe try this??


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## splitpost (Mar 21, 2011)

chad556 said:


> Ugh, I still have not been able to get this thing to run.
> 
> 
> I pressure and vac tested and could not find any leaks.
> ...


 
have you checked to see if the throttle rod is the right length eg to long wont let return to idle


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## hotshot (Mar 21, 2011)

I'd disconnect the throttle linkage, pull the carb one more time, and make sure the throttle shaft, spring, & plate are correctly assembled. The little air bypass hole in the round plate should be at the bottom & the throttle plate not bound up when you fully adjust the LA screw counterclockwise... 

Leave the linkage unhooked when you reinstall the carb, start it up and see if you can now adjust the idle properly with the LA screw. 

If it still does idle high, there's a vacuum leak somewhere & if you run the saw for long it can quickly roach the piston & cylinder. What vacuum did you test to? Should hold -7"HG to -10"HG for an hour if the seals are good.


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## splitpost (Mar 21, 2011)

also check if the trigger is comming back all the way and that no hoses are fouling around the carb and linkages


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## rxe (Mar 21, 2011)

Throttle plate in back to front? It has a bevel...if back to front it doesn't seal properly.

If there are no leaks, the the only way for air to get in (and cause the high idle) is either because:

- the throttle is not closing: rod bent, as above
- plate in back to front
- plate bent


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## ronT2 (Mar 21, 2011)

Is #5 shown in the IPL missing? I don’t see it in your parts pile. If it’s missing you might not be moving the needle off the seat.

I’d also stick with a single pump diaphragm as others have said. I wouldn’t stack two of them, one gasket and one diaphragm as shown in the IPL.

I just swapped out a rubber pump diaphragm for a clear blue plastic like diaphragm on a saw that was running or….not running like yours. That solve the whole problem, saw runs great again.


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## chad556 (Mar 22, 2011)

Hey guys thanks for all the advice, I am going to go over the carb with our mechanic tomorrow to see what is up with it. If everything looks ok and a little adjustment wont give any promising results then I am going to recheck for an air leak.

The vaccum test that I did only held vac for about 10 minutes at 10"hg. This didnt seem good but my subsequent pressure test showed only the innertube seal that i had made to seal up my exhaust port was leaking air. Since i had so much trouble sealing up the muffler I was quick to just call the test good and move on.

The muffler doesn't bolt on like most everything else i have seen. Its clamped on by a thick wire and two little wedge pieces. Therefore its almost impossible to get a firm seal around it with a piece of rubber. I am thinking of maybe using a liquid gasket material to try and seal it. If anyone has any experience dealing with this and could let me know what to do i would greatly appreciate it.



> I just swapped out a rubber pump diaphragm for a clear blue plastic like diaphragm on a saw that was running or….not running like yours. That solve the whole problem, saw runs great again.



Oh and I do have part #5 in there, the little screw that holds that tiny rod in place. I have also swithed to the black rubber pump diaphragm, but as before, no luck when using the gold, black or black and gold together for that matter. I don't think thats the problem but thanks for the suggestion. Do you know were I could find a diaphragm like that blue plastic one for this carburetor.


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## ronT2 (Mar 23, 2011)

chad556 said:


> *Oh and I do have part #5 in there, the little screw that holds that tiny rod in place.* I have also swithed to the black rubber pump diaphragm, but as before, no luck when using the gold, black or black and gold together for that matter. I don't think thats the problem but thanks for the suggestion. Do you know were I could find a diaphragm like that blue plastic one for this carburetor.



Oops…sorry I should have noticed that. The blue plastic diaphragm came in a rebuild kit for a much smaller carb. I don’t know if they’re available for a carb on an 880.



chad556 said:


> And one more thing, sorry to go on and on but it might be worth mentioning: *When i took the fuel hose out of the carb after getting the saw to run(unsuccessfully) it spewed gas out in a 12" high stream that slowly died down over about 10 seconds, leaving my gas tank almost empty and me partially covered in mixed gas. Is there supposed to be pressure build up in the fuel tank like that?* The mechanic I know didnt think it was right but wasn't sure. He said the tank should be vented and shouldnt shoot gas like that. I think hes right but I'm not sure.
> 
> Could this be causing the symptoms? Is it even a problem? I'm pretty stumped here there are about 4 things that could possibly be wrong with this thing and I am not sure where to start.



That doesn’t sound right. From what you’re describing it sounds like the pump diaphragm isn’t working correctly. It almost seems like the impulse is somehow pressurizing the fuel tank. Here’s a link to some more info that might be helpful.

Walbro WG-8 Carb Disassembly


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## rxe (Mar 24, 2011)

Fuel tanks do pressurise, but this should not be causing a high idle. If anything, it should be flooding the saw out. Check the tank breather, it might be blocked. Some modern units do deliberately pressurise the tank (MS192, KM130 that I know of), I haven't torn into an 880 to see if it is the same.

If you have a high idle, air is getting in somewhere - sounds like through the carb, as you've pressure tested the saw.


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## willbarryrec (Mar 24, 2011)

chad556 said:


> The vaccum test that I did only held vac for about 10 minutes at 10"hg. This didnt seem good but my subsequent pressure test showed only the innertube seal that i had made to seal up my exhaust port was leaking air. Since i had so much trouble sealing up the muffler I was quick to just call the test good and move on.
> 
> The muffler doesn't bolt on like most everything else i have seen. Its clamped on by a thick wire and two little wedge pieces. Therefore its almost impossible to get a firm seal around it with a piece of rubber. I am thinking of maybe using a liquid gasket material to try and seal it. If anyone has any experience dealing with this and could let me know what to do i would greatly appreciate it.
> .



One thing I have had good luck with for vac tests is cleaning the outside of the exhaust port with some carb cleaner and using some Gorilla brand duct tape to seal the exhaust port....only works for vac testing but so far it's worked for me.
Hopefully I won't learn I'm a idiot here in a post or two. :msp_rolleyes:

Good luck!
Keep on working on it and don't give up it will be well worth it,learning how to work on saws not to mention your own 120cc saw!


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## JJay03 (Mar 24, 2011)

willbarryrec said:


> One thing I have had good luck with for vac tests is cleaning the outside of the exhaust port with some carb cleaner and using some Gorilla brand duct tape to seal the exhaust port....only works for vac testing but so far it's worked for me.
> Hopefully I won't learn I'm a idiot here in a post or two. :msp_rolleyes:
> 
> Good luck!
> Keep on working on it and don't give up it will be well worth it,learning how to work on saws not to mention your own 120cc saw!


 
Think this would work for pressure test also if you then bolted on the muffler after using the tape? Same for covering the intake then bolting on the boot?


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## RiverRat2 (Mar 24, 2011)

willbarryrec said:


> Good luck!
> Keep on working on it and don't give up it will be well worth it,learning how to work on saws not to mention your own 120cc saw!



I think he ought to box it up and send it to me,,,,, and let me straighten it out for him!!!!!!!:msp_mellow::msp_ohmy::hmm3grin2orange:


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## chad556 (Mar 24, 2011)

Hey guys, thanks for the encouragement and advice. Our mechanic has been sick so he hasnt looked at the saw yet but I have the engine blocked off and tried out a vac test again. i sealed up the muffler with a piece of innertube and some form-a-gasket liquid stuff that i let cure overnight. It seems like it is failing the test it will only hold 10"hg for a couple seconds, quickly droping down to 5-7"hg and then slowly falling to zero after about 2-5 minutes. Maybe it is just a leak in my muffler seal again but I will try to be more precise with my pressure test this time and actually use a pump with a pressure gauge on it instead of trying to 'eyeball it'. It has been one heck of a learning experience, thats for sure.

In preparation for the pressure test I have ordered a flywheel puller (i can always sell it again once im done with it) and an entire kit of gaskets and seals for the crank case. Goodbye $80 but I figure I am already over $800 into this saw so what is a couple more bucks. Hopefully I can make a little money with it once I fix it up and from what I have seen lately on ebay $880 for an 880 isn't bad lol.


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## chad556 (Apr 18, 2011)

Ok, I have an update on the situation. The other day I finally was able to screw a pipe into the flywheel and weld a nut into it and, after several hours of frusteration, finally get the thing to pop off. 

Underneath i found out that the seal was cockeyed a bit, flush on one side, sticking out by a mm or so on the other. This would be the cause of the symptoms im experiencing right? Now my question is: Should i try to just tap the seal back into place or should I try to replace it with a new one(i have the seal and gasket kit)? I would hate to put this together and have it not work.

I also sealed off the muffler with a rubber tube and gasket maker so i will test the pressure holding before I go ahead with reassembly. I think I have found the answer to the problem though. Any insight from successful air leak fixers would be great :smile2:


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## betterbuilt (Apr 18, 2011)

You could put pressure to it. Then put some oil over the seal and see if it bubbles.


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## gink595 (Apr 18, 2011)

Air leaks suck! I'd put a new seal in it, or tap it in and see if it leaks. That's a judgement call there.


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## hotshot (Apr 18, 2011)

Gink is exactly right....if any doubt, pull it out & replace it. 

I found that you can slip an oiled toothpick between the shaft & an old questionable seal that has lost most of it's memory (like I have), & then the seal will refuse to set back down onto the shaft for up to three or four minutes. Vacuum testing will drive you nuts on those old intermittent seals.


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## chad556 (Apr 30, 2011)

Thanks for the continued support. I decided to replace the seal, tapped the new one in and redid the pressure/vac test. This time I used Ultra Blue Gasket maker around my muffler port and stuck my rubber piece there overnight. It is air tight.
Unfortunately the rest of the saw wasn't. I checked and checked and couldnt find how this thing was losing air. The pressure test is hard because I am using a bike pump that slowly looses pressure on its own. The vac test is solid though and does not lie to me at least I think (I am suspicious that the decomp valve doesn't have enough strength to keep air from slowly seeping in).

I was about ready to give up when I remembered something I read here about dunking the saw. Sounded like just the crazy Idea that i needed to try, Heres how it went:

[video=youtube;CdXG8nH20Mk]http://www.youtube.com/watch?v=CdXG8nH20Mk[/video]

Is that leak from the crank case that bad? It is at the bottom of a tiny little "hole/depression" molded right into the metal of the crank case itsself. It seems like just a tiny crack or pinhole, couldn't even see it with a magnifying glass. To be safe I put some epoxy around it and blew it around with compressed air until it was coated all around the area. I then hooked up my vac pump in hopes the vacuum would draw in the epoxy and make the patch job better. It held vacuum 10"hg for about 20 minutes. I then started to put the saw back together and then pumped up the vac pump agian and left to go home. If it is still holding tomorrow it will be very encouraging. I will dunk it one more time tomorrow to see if the leak is really fixed or not and if so I will put it back together and cross my fingers again.

I really wish I had tested that crooked seal now. It would have been nice to know if that was 100% surely 'the' leak or not. Oh well. If the vac/pressure tests are passed and I have two carbs to play with i can't be too far away from solving this mystery. I just want to cut some wood with this baby. :chainsawguy:


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## chad556 (May 1, 2011)

Well, the good news is that it held a vacuum for 20 hours overnight. I left it at 10"hg and when i came back it was still holding 7"hg. I think thats safe to say there there is no significant air leak there right?

So I excitedly put the saw back together for what I hoped was the last time. Fired her up and low and behold it was the same problem all over agiain. Two different carburetors both had the same problem as well and I have tried at least 3 different batches of fuel. Unless anyone has any other ideas I should try I think its getting to the point where I have to decide weather to sell it whole as not running or cut it up and sell it piece by piece:msp_sad::bang: Its getting harder and harder to pull that cord knowing that its probably going to be the same old bad news again and again.:help:


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## GA_Boy (May 1, 2011)

what about the impulse line? Have you looked at the intake boot?


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## Andyshine77 (May 1, 2011)

This may sound stupid, but have you been using the same spark plug? I've had a few plugs go bad, and they can really make one scratch their head.


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## betterbuilt (May 2, 2011)

Don't give up yet. I think you need another set of eye's on it. I have a 066 that's doing something similar. I just have to take a brake from it and go back to it when I have the patience to look at it again. 

I bought all new rubber lines to replace the ones I had just bought because the air leak wouldn't go away. Have you tried a pop off tester like Gink recommends in the thread I started. 
http://www.arboristsite.com/chainsaw/171064.htm

I made one from the parts I had bought for pressure testing my saws.


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## chad556 (May 2, 2011)

Both Impulse line and intake boots are fine, passed visual inspection and didnt leak for pressure or vac test. I have used two different spark plugs. One that was brand new and worked just fine in an MS441, good advice though, its always the spark plug (unless you have my luck, lol).

I am intrigued by your thread, betterbuilt. A leak in the carburetor would explain a lot. The original carb I rebuilt (several times) with no luck, used an 084 carb kit because thats all I could find. I also picked up a used 084 carb on ebay for 40 bucks and that had the exact same problem as the original 880 carb. Could they both have leaks? And how do you test them, I am pretty sure i could round up the parts to make a tester but what do I hook up to what? and what do I plug?... and what am I hoping to see for that matter? I'm wrapping my mind around this stuff somewhat better but carbs are still like magic to me  so small yet so much delicate stuff going on in there.


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## RiverRat2 (May 2, 2011)

chad556 said:


> I am intrigued by your thread, betterbuilt. A leak in the carburetor would explain a lot. The original carb I rebuilt (several times) with no luck, used an 084 carb kit because thats all I could find. I also picked up a used 084 carb on ebay for 40 bucks and that had the exact same problem as the original 880 carb. Could they both have leaks? And how do you test them, I am pretty sure i could round up the parts to make a tester but what do I hook up to what? and what do I plug?... and what am I hoping to see for that matter? I'm wrapping my mind around this stuff somewhat better but carbs are still like magic to me  so small yet so much delicate stuff going on in there.



a squeeze bulb like a blood pressure tester cause it has a check valve /get a small pressure guage, 0-30 psi, and a T fitting to put the guage inline with the hose and an assortment of hose barb fittings to slip in the pressure hose,,,

with the carb and fuel system intact, remove the fuel tank cap and use a wire hook to fish the pick up body (fuel filter) and fuel line end out of the fill hole, remove filter,, insert the pressure tester hose barb fitting in the end of the fuel line where the pick up body was and pressure up to approx 17 psi it should hold that pressure indefinitley


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## betterbuilt (May 3, 2011)

chad556 said:


> Both Impulse line and intake boots are fine, passed visual inspection and didnt leak for pressure or vac test. I have used two different spark plugs. One that was brand new and worked just fine in an MS441, good advice though, its always the spark plug (unless you have my luck, lol).
> 
> I am intrigued by your thread, betterbuilt. A leak in the carburetor would explain a lot. The original carb I rebuilt (several times) with no luck, used an 084 carb kit because thats all I could find. I also picked up a used 084 carb on ebay for 40 bucks and that had the exact same problem as the original 880 carb. Could they both have leaks? And how do you test them, I am pretty sure i could round up the parts to make a tester but what do I hook up to what? and what do I plug?... and what am I hoping to see for that matter? I'm wrapping my mind around this stuff somewhat better but carbs are still like magic to me  so small yet so much delicate stuff going on in there.


 
You know we are having almost the same luck. I too bought a used carb of of ebay. 

The tester was easy to build. It really tells you quickly you have problems. My carb was leaking air every time I turned my head. It seem strange but apparently my skills for rebuilding a carb weren't up to par. I never did find anything in my carb but it definitely wouldn't seal about half the time. 

The new used carb I got I didn't do anything to but open it up to be sure it wasn't all gross or missing parts. I put it on the saw. and it seems to run now. There is a problem with the low side but when I got the saw the Low side was turned out quite a bit so I bet there's more to it. The saw was running okay for the first try. Now I'll deal with that low side screw and see if I can find anything.


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## betterbuilt (May 3, 2011)

RiverRat2 said:


> a squeeze bulb like a blood pressure tester cause it has a check valve /get a small pressure guage, 0-30 psi, and a T fitting to put the guage inline with the hose and an assortment of hose barb fittings to slip in the pressure hose,,,
> 
> with the carb and fuel system intact, remove the fuel tank cap and use a wire hook to fish the pick up body (fuel filter) and fuel line end out of the fill hole, remove filter,, insert the pressure tester hose barb fitting in the end of the fuel line where the pick up body was and pressure up to approx 17 psi it should hold that pressure indefinitley




17psi. I've been using 10psi. Should I go higher?


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## Saw Dr. (May 3, 2011)

chad556 said:


> Both Impulse line and intake boots are fine, passed visual inspection and didnt leak for pressure or vac test. I have used two different spark plugs. One that was brand new and worked just fine in an MS441, good advice though, its always the spark plug (unless you have my luck, lol).
> 
> I am intrigued by your thread, betterbuilt. A leak in the carburetor would explain a lot. The original carb I rebuilt (several times) with no luck, used an 084 carb kit because thats all I could find. I also picked up a used 084 carb on ebay for 40 bucks and that had the exact same problem as the original 880 carb. Could they both have leaks? And how do you test them, I am pretty sure i could round up the parts to make a tester but what do I hook up to what? and what do I plug?... and what am I hoping to see for that matter? I'm wrapping my mind around this stuff somewhat better but carbs are still like magic to me  so small yet so much delicate stuff going on in there.


 
OK, I have not been following this until today. No offense, but it seems you are going about this the hard way... The rubber bits on saws are generally the weak spots. Even if the intake/impulse line passes a visual inspection, and pressure test, they could still be bad. Both the intake and impulse are part of the A/V system. The engine is not vibrating when you test it. Vibrations could be opening up cracks in the line that you don't see otherwise. If you have not changed the fuel line, that is a very inexpensive thing to try. I doubt two carbs are bad, but if you blew them out with high pressure air, they are bad now. There are check valves in those carbs that will be damaged by high pressure air. You should only use the little tube from a carb-cleaner can to clean them, or an ultrasonic cleaner. 
I am interested in how you are testing the press/vac on the saw. If you are getting a good test, try flexing the a/v system while at it and see if the press drops. Also, where are you accessing the press to do the test? If you are using the impulse port, you are eliminating the impulse line from the test.
There are only so many places it could be leaking. The saw is obviously running very lean. You may also want to post up pics of the the mixture adjustment needle tips. I have seen a handful of carbs where "experts" have wound the needles in too tight, and broken the tips off when unscrewing them. Since the caps were missing when you got it, this is always an option.


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## chad556 (May 3, 2011)

Saw Dr. said:


> OK, I have not been following this until today. No offense, but it seems you are going about this the hard way... The rubber bits on saws are generally the weak spots. Even if the intake/impulse line passes a visual inspection, and pressure test, they could still be bad. Both the intake and impulse are part of the A/V system. The engine is not vibrating when you test it. Vibrations could be opening up cracks in the line that you don't see otherwise. If you have not changed the fuel line, that is a very inexpensive thing to try. I doubt two carbs are bad, but if you blew them out with high pressure air, they are bad now. There are check valves in those carbs that will be damaged by high pressure air. You should only use the little tube from a carb-cleaner can to clean them, or an ultrasonic cleaner.
> I am interested in how you are testing the press/vac on the saw. If you are getting a good test, try flexing the a/v system while at it and see if the press drops. Also, where are you accessing the press to do the test? If you are using the impulse port, you are eliminating the impulse line from the test.
> There are only so many places it could be leaking. The saw is obviously running very lean. You may also want to post up pics of the the mixture adjustment needle tips. I have seen a handful of carbs where "experts" have wound the needles in too tight, and broken the tips off when unscrewing them. Since the caps were missing when you got it, this is always an option.


 
Wow, I have just been educated.

I did clean out my carbs with an air hose with the regulator turned down. They didn't work before cleaning though either but I was aggressive with the air and tried to get everything out of it that i could. It looks like i will need to test them both the be sure. The needles on the original one were fine though I took them out and they were both intact. These check valves in the carbs, can they be repaired or rebuilt?

My pressure testing procedure consists of blocking off the exhaust and the intake port between the rubber intake boot and the actual carburetor. I connect my pressure/vac hose directly to the impulse line so both the boot and impulse line are pressurized/vacuumed during the tests. I'm am using a Harbor Freight brake bleeder for the vac tests and a manual bike pump with a digital gauge for the pressure tests. Good point about the anti vibration system. I rotated the crank by hand during the test without losing anything but I should have checked the lines. especially when the thing was underwater.

I guess I will start with the carburetors and if they pass I will try to pinpoint something in the impulse line.

Thanks everyone for taking the time to share your knowledge, It means a lot and I am learning a ton:msp_smile:.


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## chad556 (Dec 12, 2011)

*I almost got it I think...*

[video=youtube;MU2fFRpsof4]http://www.youtube.com/watch?v=MU2fFRpsof4[/video]

So I finally had time to go through both carburetors again. I used the old 084 carb i got off ebay and took all of the best parts and built it up good and sprayed it down with carb cleaner. Installed it and got my video camera running to capture the first test.

I hate to ask a noob question after coming this far. But at this point, what the heck am I supposed to do now?

I have the carb set to factory settings, one turn out from the stop on both H and L screws and I set the idle screw as high as it would go(yes, i know how the idle screw works, one turn goes through the whole range) to start out with. I got the results you see in the video. I am afraid to touch this thing anymore because I am paranoid I will blow it up. When I rev it up it sounds like its revving a bit high to me and obviously, it idles low now, but too low to sustain its self. Compression with the new piston is 150+ psi, spark plug is brand new and spark is strong, gas is pretty new etc...

Does anyone notice anything I am missing here? In the past I have just fiddled with the carb to get it where I needed it, I don't really know what I am doing when it comes to adjustments and I will be the first to admit it. Can anyone explain exactly where I would go from here? L screw first? or H screw? Basically if it were you in that video where would you put the screwdriver and which way would you turn it? Thanks in advance guys, sorry for the noob question but i am terrified i will destroy this expensive beast with my inexperience. I am just about ready to take it to the dealer and have them tune it for me but I would rather learn and keep my money if some one is willing to teach!


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## splitpost (Dec 12, 2011)

bring your idle up and then get your low side set


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## StihlyinEly (Dec 12, 2011)

splitpost said:


> bring your idle up and then get your low side set



+1

I just saw this thread after it got bumped back to the top. Chad, you've come a long way with this saw, and it looks like you are almost there.

I don't have the specs for the 880, but turn your idle screw clockwise to speed up the idle a bit and set your L screw at whatever your shop manual tells you, and adjust the L further from there if you need to.


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## chad556 (Dec 14, 2011)

Ok so it looks like i am stuck with more problems.

I started yesterday with both H and L screws out 1 full turn as per the manual for factory settings, The idle speed was set at about 90%. The saw fired up and idled for a little then sputtered out.

I then proceded to turn the L screw out (Left/CCW) about 1/4 turn.

Saw fired up again, sputtered and died even quicker this time. So i went back in with the L screw about a half turn(Right/CW) so now i am at 3/4 turn out from the stop on the low idle screw

Tried to start the saw again and it flooded on me, wouldnt fire at all. Also it started doing that thing where it gets so hard to turn over it pulls the starter cord right out of your hand. I was tired of wrestling with it so i let it sit to dry out overnight.

So that brings me to today, I go to start the saw up and on full choke i could not get it to fire. After 20 or so pulls I look it over and notice blackish oil/gas mix coming out of the muffler, and decomp valve. I pull of the spark plug which is saturated in gas and give the cord a couple pulls to see whats in there. Gas spews out of the spark pulg hole, a lot of gas. So i pull the muffler which has a small puddle of gas in the bottom and flip the saw upside down. Gasoline starts pouring from the carb, exhaust and spark pulg hole. probably *almost an ounce of gasoline *spills onto the floor.

Now I have flooded things before but this does not seem normal. Could this be another carburetor problem or is it how I have been going about setting the screws on the carb itself?

I currently have the parts off the saw I mentioned and its hanging in my garage with an empty fuel tank hopefully drying. Any advice would be great!


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## In The Weeds (Dec 14, 2011)

After all that you have gone through I don't think bringing it in to be tuned and maybe asking questions would be considered giving up.


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## chad556 (Dec 15, 2011)

Yeah its looking that way. I think i will give it one more go once i get it together again and then its off to the dealer to see what they think of it. I have a tachometer coming in the mail so hopefully i can get it to a point where it at least stays running long enough to get some useful data out of it.

For my next attempt i am thinking of starting with the H screw at a half turn and the L screw at 1/4 turn out from the closed position. As i understand it this will make the engine run more lean and cause the rpms to be higher, also leaner running will reduce the flooding issue i hope. Basically i just need it to keep on kicking enough for me to get a screw driver in there and dial in a nice angry sounding idle. From there i will move onto my H screw and hopefully with the help of my new tachometer i can get that tuned into where it needs to be.

Am i going about this the right way? I have never tuned "from scratch" before so how is it done guys?


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## betterbuilt (Dec 15, 2011)

Bump


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## chad556 (Dec 17, 2011)

Here is how far I got today:

[video=youtube;f1FOLP_PXFU]http://www.youtube.com/watch?v=f1FOLP_PXFU[/video]

Its is detailed and annotated with how far out from the stops the screws are turned out. Idle screw is set at about 75% all the way through the video though at some point towards the end i do bump it up a bit.

Its close but i still cant get it to run. When i got it to idle for a bit it died right when i picked it up and hit the throttle.

I'm scared to really rev it up because i don't have a clue what this should sound like at its max rpms, just hoping my tach will come in the mail soon. it sounds pretty good in the video but I would hate to blow it up agian.

Also the spark arrestor screen is not in the muffler. Would this make it easier on me if i replaced it?

Would repalcing the hoses maybe make a difference? the fuel line feels pretty stiff to me.

Any of the finer points of carb tuning that i'm lacking here?

Thanks in advance, you guys have been a great help, I wouldn't have gotten this far if it weren't for you!


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## gink595 (Dec 17, 2011)

All of the HT carbs I had all of them had a problem and I got them figured out using a pop off tester. Every single one of them had a air leak in a different spot. One was at the fuel inlet elbow, the other had a small defect that wouldn't let the pump diaphram seat against the body of the carb. And the other wouldn't hold seat pressure and would drip fuel. Without that gage I was pulling my hair out.


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## In The Weeds (Dec 17, 2011)

Great thread, got to admire your perseverance. opcorn:


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## RiverRat2 (Dec 17, 2011)

gink595 said:


> All of the HT carbs I had all of them had a problem and I got them figured out using a pop off tester. Every single one of them had a air leak in a different spot. One was at the fuel inlet elbow, the other had a small defect that wouldn't let the pump diaphram seat against the body of the carb. And the other wouldn't hold seat pressure and would drip fuel. Without that gage I was pulling my hair out.



I agree with Gink595,,,,I think If you dont have a pressure tester,,, Take it to the shop,,, I check them all the time,,, lay it on its side like you gonna fuel it open gas tank, I have a wire hook that I made and fish the pick up body out of the tank, leave the hook behind the big rib on the fuel line just before the pick up body, pull the pick up body off, insert the hose bib fitting on the tester and pressure it up,, it should hold about 4.5 bar or around 16 psi indefinitly...

Im just curious,,, if it is flooding that is usually a stiff metering diaphragm or a fuel inlet lever setting that is too high or a inlet valve anomoly,,,,, JMHO,,,,,I dont think trying to adjust the carb by leaning it out is the answer,,,


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## blsnelling (Dec 17, 2011)

I believe your L is still too lean. Back it out another 1/4 turn. Once it's running, slowly turn it back in. You'll hear the idle increase. At some point, it will stop increasing and just want to die. Back it back out 1/8-1/4 turn. Fine tune for throttle response. 

You'll have to tune the H needle in the cut since the saw is rev limited. You want it to 4-stroke when you let off the load, than then clean out with a load.


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## chad556 (Dec 18, 2011)

Thanks for all the responses guys! Hopefully I will have time to play around with it tomorrow. I am hoping it is just an adjustment that I need and the carb doesnt need work. If i have to take it in then i guess thats that though...

That pump diaphram that i used was the best of the three i had. One was stiff and brittle like a dry leaf but the other two were in pretty good shape. Once I get that idle solid, and it doesnt cut out when i hit the gas I think I can finally call this project a done deal.


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## In The Weeds (Dec 18, 2011)

When you are all done I would be interested to know how much you have into the saw altogether to date?


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## chad556 (Dec 18, 2011)

Well so far I have:

The ms880 powerhead: $650
Piston kit from ebay: $35
Bar and chain from baileys: $90
Carb kit from ebay: $13
084 Carburetor from ebay: $40
Fuel filter from ebay $8
Gasket and seal kit from ebay: $35

Total money in the saw thus far: $871

I think thats everything as far as parts and accessories, i bought a few new tools too.

Flywheel puller: $40 (could probably sell it now)
t27 driver to reach the cylinder head screws: $5
Brake bleeder kit to vacuum test: $20
hydrocloric acid to clean out the jug: $10
Tachometer: $20

So there is another $95 worth of tools to add to the collection :smile2:. Man, i love tools.

Overall not such a bad investment. I would guess i could at least get my money back if I sold it on ebay or craigslist. Just the other day I saw a near brand new ms880 that was siezed go for over 1000 on ebay. I think after what I have been through with the baby i will want to cut some wood with it first though. In fact i am off to attempt just that. If it doesnt work out I guess I will be taking it to the shop on monday though. I at least want to get a new fuel line that goes between the carb and the tank. That thing is stiff and the clip is so warn out and weak that i would put my money on that spot being an air leak if there is one especially under vibration. I want to fix it just for peace of mind.


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## gink595 (Dec 18, 2011)

I think posting on this thread has jinxed me:hmm3grin2orange: I went out and put a bar and chain on mine and now I think I have carb problems....fark me!!! I swear me and these HT carbs just ain't meant to be! I wonder if a 3120 carb would fit up?


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## fearofpavement (Dec 18, 2011)

*IF there was a way...*

If you could find anyone close to you that has a running 880, it would be very interesting to see if your carb would run on their saw and vs vs. I have had very weird mechanical problems with different things in the past and finally only resolved them by finding a clone of it and playing musical parts until I was able to move the problem from one piece to the other.

ie, if your saw runs with a known good carb, then you know that's the problem. If it doesn't run well, but the other saw runs fine with your carb then you know the carb isn't the problem and so forth.

You had the flywheel off, was your woodruff key in good shape?


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## showrguy (Dec 18, 2011)

hey chad,
just watched your video, when the saw shut off at the end i thought we were going to see a sledge hammer smashing on it !!!
if you can't find a for sure good carb i'd be willing to take mine off and send it to you to try, just to be sure it's the carb.... i know my880 is good to go...
you gotta promise not to mess with it though....he,he,he


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## chad556 (Dec 18, 2011)

fearofpavement said:


> If you could find anyone close to you that has a running 880, it would be very interesting to see if your carb would run on their saw and vs vs. I have had very weird mechanical problems with different things in the past and finally only resolved them by finding a clone of it and playing musical parts until I was able to move the problem from one piece to the other.
> 
> ie, if your saw runs with a known good carb, then you know that's the problem. If it doesn't run well, but the other saw runs fine with your carb then you know the carb isn't the problem and so forth.
> 
> You had the flywheel off, was your woodruff key in good shape?



Thats good advice, if i had followed that months ago i'm sure it would have saved me a lot of work lol. I have actually played musical parts with two carburetors and I think the key now is to keep playing it. I am going to look closely at the metering diaphragm and make sure I have the best one in there. I think i will also switch out my current fuel pump diaphragm (gold one) for one of the black rubber ones that I have. It might just be incompatible with the fuel i'm using. Also, the key was in good shape on the flywheel and went back in without a hitch, good point though, that would throw the timing off some...

I took it for another test run today and Brad was right, just a little richer on the L screw and it purred away indefinitely with some fine tuning. At that setting however I could not rev the saw up at all. I would hit the gas and get a gurgling sputter and then the engine would stall. I gave the H screw a few adjustments from a half turn to 2 full turns and the best i could get it was around the 1 turn range where it would gurgle and the chain would spin at half speed (i would guess around 4k to 7k rpms). After a while the saw got harder and harder to start and felt like it was flooding so I put it back on the shelf for the day. When i turned it on its side i could hear the gas leaking out of the muffler and sizzling on the cylinder. This sounds just like river rat's diagnosis to me and I will be going over that diaphragm and everything near it.

So my game plan for tomorrow is to:

replace the fuel pump diaphragm with the best black one i have.

double check and see if my metering diaphragm and related parts are working as they should.

go to the shop and get a replacement for my fuel line. probably not the problem but its another possible issue i can prevent. I am having doubts that it is sealing effectively against the little plastic elbow fitting at the top of the carb.

repeat my process of tuning it and hope for the best, if no luck there then i will probably have to finally just take it in to be looked at. When i'm there tomorrow I will try to pick the guys brain and see if he has any experience with these kinds of carbs, hey you never know.

Oh and Showrguy, lol, you know if I had been wearing my steel toed boots i probably would have contemplated booting it across the driveway and selling the salvageable parts on ebay :hmm3grin2orange: Seriously though, thanks for the offer on the carb. I think i have the problem narrowed down pretty well now. Every time I mess with the carburetor i get different results so that seems like a good sign. Hopefully one of my little tweaks works out but I will let you know if I want to try one out thats good to go.

Thanks for all the input guys, you've helped me out immensely. I will be sure to let you all know how it works out!


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## Blamo (May 17, 2013)

*I am in suspense*

What happened? I know that this is an old post but, I am new to the site and have been following along like I am reading a good book. This ending is terrible. Does Chad move away from the city to pursue his dreams of starting a logging company? Does he finally get the girl? More importantly, did Chad get that dang saw working?


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## bgreen (Jan 11, 2016)

I have a 390 that is having a problem at high rev runs up good then starts to stall out, but it will idle all the obvious things have been done rebuilt carb checked top end and crankcase pressure no holes in any of the lines checked out the torque on the cylinder bolts tried a brand new stock ignition still the problem persist. Looked at the cylinder there is some light scoring below the exhaust port and a very little above the intake port it is not flooding but there seems to be a lot of excess fuel in the cylinder. To much dirt ingestion replace the top end?


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## fearofpavement (Jan 11, 2016)

Sounds like a fuel issue. Try switching carbs with another saw. (there's a lot of these around, find a buddy to see if you can move the problem)

Is the fuel hose an aftermarket one? If so, that could be the issue as most don't work properly (they pinch off on this model saw)

I just had a similar problem on an MS390 this afternoon. It would cut great about halfway through a 12" log and then bog down. I pulled the carb, cleaned it, slightly tweaked the metering lever height and put it back together. Runs great now.


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## fearofpavement (Jan 11, 2016)

The above applies primarily to the Stihl MS390. If you meant a Husqvarna 390, some but not all is applicable.


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## bgreen (Jan 12, 2016)

Thanks for the response it is a Husqvarna. Had a friend tell me the same thing about the carb issue, gonna try that it has a new stock fuel in it but I will check it for a pinch.


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## bgreen (Jan 12, 2016)

Dropped in a new carb bingo back in the run. Again thanks for the assist.


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## Maintenance supervisor (Apr 8, 2020)

Plastic fuel inlet is always bad.


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## laro4444 (Oct 26, 2020)

chad556 said:


> Thats good advice, if i had followed that months ago i'm sure it would have saved me a lot of work lol. I have actually played musical parts with two carburetors and I think the key now is to keep playing it. I am going to look closely at the metering diaphragm and make sure I have the best one in there. I think i will also switch out my current fuel pump diaphragm (gold one) for one of the black rubber ones that I have. It might just be incompatible with the fuel i'm using. Also, the key was in good shape on the flywheel and went back in without a hitch, good point though, that would throw the timing off some...
> 
> I took it for another test run today and Brad was right, just a little richer on the L screw and it purred away indefinitely with some fine tuning. At that setting however I could not rev the saw up at all. I would hit the gas and get a gurgling sputter and then the engine would stall. I gave the H screw a few adjustments from a half turn to 2 full turns and the best i could get it was around the 1 turn range where it would gurgle and the chain would spin at half speed (i would guess around 4k to 7k rpms). After a while the saw got harder and harder to start and felt like it was flooding so I put it back on the shelf for the day. When i turned it on its side i could hear the gas leaking out of the muffler and sizzling on the cylinder. This sounds just like river rat's diagnosis to me and I will be going over that diaphragm and everything near it.
> 
> ...


How this woked out ????????I am having same issue, read all those post and ..........please let us know ?


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## keepreal (Oct 26, 2020)

chad556 said:


> Ok so today I went out to pursue a great find on CL, a nice ms 880 for $650 (I was set on finding a 660 for that price). The guy said the reason for the low price was that the saw would start but would not idle, it would just rev up to half throttle, sputter and then quit, I figured simple enough just a little tweaking and I could get it running strong again, probably a carb issue. Well, the whole story was that he took it to his local stihl dealer and they told him that the piston and clyinder were bad, causing the saw to rev up fast when it was started instead of idle like it should. This seemed kind of strange to me, the saw obviously has decent compression (nearly ripped my fingers off trying to start it) The dealer told the guy $700 to replace the piston and cylinder to get the saw running again.
> 
> Probably against my better judgement I shelled out the cash anyways and took the saw home. Cleaned it up, cleaned the carb and started experimenting with the High Low and Idle screws. No luck, the longest i got it running was about 20 seconds and it wildly revs up and down, It wont go down to idle when i take the trigger off and when i go to full throttle the saw only goes up to ~1/2 to 3/4 throttle at best and then "pulses" (sounds like somethings going to break.) I don't have a bar and chain for it, all of mine are 3/8" and dont fit on the bar studs. I am getting a 36" carlton one from baileys. Is there anything about this that seems wrong to any of you? (I admit I am a novice when it comes to tinkering with chainsaws) Could it really be the piston and clyinder are bad? I wouldnt think it would fire at all if that were the case? Im stumped and I dont want to spend more money or make a bigger mess than i have to, can anyone give me a place to start or point me in the right direction?


Hey,buddy,you can check on ***********.They might can give you some help.


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## STIHLMECHANIC (Oct 30, 2020)

impulse line..has a hole in it


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## RajElectric (Oct 21, 2021)

I'm having the same issue on an 088, holds vac and pressure all day, good compression, clean P and C, recond carb, fuel line holds vac and pressure, runs high idle then dies lower RPMS. I have a coil on order.


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## PP4218 (May 19, 2022)

chad556 said:


> Thats good advice, if i had followed that months ago i'm sure it would have saved me a lot of work lol. I have actually played musical parts with two carburetors and I think the key now is to keep playing it. I am going to look closely at the metering diaphragm and make sure I have the best one in there. I think i will also switch out my current fuel pump diaphragm (gold one) for one of the black rubber ones that I have. It might just be incompatible with the fuel i'm using. Also, the key was in good shape on the flywheel and went back in without a hitch, good point though, that would throw the timing off some...
> 
> I took it for another test run today and Brad was right, just a little richer on the L screw and it purred away indefinitely with some fine tuning. At that setting however I could not rev the saw up at all. I would hit the gas and get a gurgling sputter and then the engine would stall. I gave the H screw a few adjustments from a half turn to 2 full turns and the best i could get it was around the 1 turn range where it would gurgle and the chain would spin at half speed (i would guess around 4k to 7k rpms). After a while the saw got harder and harder to start and felt like it was flooding so I put it back on the shelf for the day. When i turned it on its side i could hear the gas leaking out of the muffler and sizzling on the cylinder. This sounds just like river rat's diagnosis to me and I will be going over that diaphragm and everything near it.
> 
> ...



What was the final outcome?


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## JosephSalesky (Nov 19, 2022)

Dudes, same problem with my 880. What was the outcome?


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## Dennisthemenace (Nov 19, 2022)

Air leak


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