Stihl MS880 runs at high idle then dies.

[chad556]

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?

 

[mdavlee]

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?

 

[THALL10326]

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...

 

[mikefunaro]

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.

 

[rob066]

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

 

[chad556]

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.

 

[mikefunaro]

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...

 

[pioneerguy600]

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

 

[mikefunaro]

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

 

[chad556]

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.

 

[chad556]

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

 

[jimdad07]

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.

 

[chad556]

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?

 

[chad556]

[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?

 

[mikefunaro]

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.

 

[chad556]

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.

 

[pioneerguy600]

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

 

[mikefunaro]

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.

 

[josh1981]

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

 

[shawn022]

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.