ms 390 bashing

[sawinredneck]

Now I'm really cofuged!!!!!!!!

Took it out and ran 3/4 tank through it, I had a fairly dull chain halfin some of the larger peices, with the gain, on white oak, a decent work out with the 25" bar. Pulled the rope 5 times lit right off, never skiped a beat. shut it off let it sit, first pull! Ran it some more, let it sit, first pull.
I am leaning back to the vapor lock now?
Andy

 

[BlueRidgeMark]

No loose insulation or cuts in the wires, that I noticed?

You need more than an eyeball to check a coil. You can have bad insulation where you can't see it, and sometimes it only fails under load.

 

[sawinredneck]

I do understand that, worked on too many JD lawn tractors with wiring gremlins in the past to know that even a fingernail will miss some. But it is a relativley new saw, 3mos., and nothing is rubbing anywhere. As for the coil being warm, ripping 22" long peices of white oak with a semi-dull chain on a 25" bar, I don't know how to load it much more than that!
Andy

 

[THALL10326]

I do understand that, worked on too many JD lawn tractors with wiring gremlins in the past to know that even a fingernail will miss some. But it is a relativley new saw, 3mos., and nothing is rubbing anywhere. As for the coil being warm, ripping 22" long peices of white oak with a semi-dull chain on a 25" bar, I don't know how to load it much more than that!
Andy

Man that is a weird one there. Sounds like she running perfect. A intermediate problem is always the hardest to sovle, no question about that.
Since its running good at the moment keep running it and be aware of any changes should she start to act up. Tomorrow I'm going to call down at Stihl and ask some questions on your behalf and see what they think is causing that saw to run perfect and than act up and then run perfect. I'll point out everything you said and we'll see what they think it is and I'll get back to ya on it tomorrrow evening with they think it is or what they think you should be looking for. One way or the other its a problem I know is giving you a headache and we can't be having that so hang tight, help is on the way.....

 

[manofstihl]

ms390 is a homeowner saw

Nothing wrong with the 029,039. ms290, 310, 390 family as long as you are not planning on using it all the time. The main problem I have with these saws is weight. they are too heavy, and that is the price you pay for getting that saw so cheap. Reliability seems to be good on them and although they are a pain to work on due to the plastice engine housing and jug configuration if you take careof it and don't drop stuff o it it will be fine. I would point out that an ms440 weighs less and will kick the 390 'stail- but then, it is a PRO saw..................

 

[Andy1234]

I have a 390 that I purchased over the winter, and I am very pleased with it. I have a 20" bar on it, with a full chiesel chain. I've cut over 20+ cords with it, and it still runs great. Unfortunately, now the neighbors come find me when there is a big tree to cut.
This weekend, I dropped a 90+ foot tall Red Oak with it. The stump measured 31" across. It worked like a charm.
Let it sit for a month, throw it in the truck and off I go. Give it 4-5 pulls on choke and it coughs, set it to half choke and one more pull and we're off!
It doesn't go through gas like a pig, either. Typically a full tank lasts 30 min of steady use.
It may be 2 lbs too heavy, but it works great for me.
But, that being said, I'm still looking for a 440....

 

[madmax]

This is prob a stupid question but have u checked the filter in the tank or the screen in the carb?

 

[Fish]

Sounds to me like your saw got a bit of water or trash inthe tank,
and most of it has worked out of the carb.
It might be running ok now, but there may still be some crud in the carb.

You need to learn one thing though, if the saw is running squirrelly, don't
keep trying to run it, you can easily damage the piston. Find out why it is
running poorly.
If it was up to me, I would go through the carb, take it apart, remove the
needle, and blow out the crud. Also take a good look at the fuel line for
cracks, as Stihl uses crap for their fuel lines here lately. Reassemble, the
carb using the old diaphragms. You should become comfortable rebuilding
a carb, as that is usually the culprit when saws run poorly. If one finds
a fuel line full of cracks, he should go through the carb as well, as the carb
will have dirt/dust in it from the cracks.

 

[sawinredneck]

Thanks Thall

Fish, I get what you are saying for sure, the thing is still under waranty, and as Thall pointed out, and I remeber all too well with my experiences, it has to act up to be able for them to fix it!
As for checking the filter, I will no problem there, but not going to tear into the carb just yet, again, that waranty deal.
Andy

 

[THALL10326]

Fish, I get what you are saying for sure, the thing is still under waranty, and as Thall pointed out, and I remeber all too well with my experiences, it has to act up to be able for them to fix it!
As for checking the filter, I will no problem there, but not going to tear into the carb just yet, again, that waranty deal.
Andy

Ok my friend I called one of the high dollar techs down at Stihl today and discussed your saw problem with him. I explained to him exactly what you told me and the first thing he said was check all the wiring going from the on/off switch all the way to the coil. I told him you had done that and he asked if its running ok now. Meaning if you had a short between the wires and you moved them alittle bit while checking them you may have removed the short temp. till it comes in contact again. So how is it running at the moment?, any better since you checked the wiring? Secondly he said if the wiring was check ok and its still running like its cutting off and on then most likely you coil is going south. He said coils going bad can make a saw do some crazy stuff. I asked him about vapor lock and he said thats a possiblity but you have to listen to it close and decide is it losing fire or losing fuel. Other words you need to really listen to it close to detect which one it is. A saw that misses sounds like its being cut off for a split second and turned back on. To get a idea of what it sounds like flipped the switch on and off on purpose so you will know exactly what your listening for when your using it.
He really didn't tell me anymore than I already told you. I will say this however. Being you got such a intermadiate problem there its going to be hard for the shop to find it because they aren't going run tanks of gas through it waiting for to act up. I say since you got 9 months left on your warranty just run it. If it keeps acting up put a muffler on it and take it back. Tellem whats going on and dont stettle till its fixed. Once it goes in the shop your warranty is good untill its fixed. If a saw such as your's came in my shop I wouldn't even attempt to wait for it to act up. I'd put it in a box and send it to Stihl. They have all the high dollar equipment to test the coil and everything else on that saw and they will get it right before it leaves, thats a positive. That may well be you best route. Use your warranty when all else fails. Dont wait till its gone. Sorry I couldn't get you some more usefull info but thats all he coudl tell me. Keep us posted on how that thing does. I'm as curious as you to know what is causing the problem.....

 

[Lakeside53]

There is a dead simple Ignition tester from Stihl (almost all stihl shops have one) that is called a ZAT-4. It runs in-line with your plug and ignition wire. Works great for intermittent failures. Plug it in, run the saw, and you'll soon see if you loose igniton... if you see no flash from the neon, you have no spark..

 

[Diesel JD]

Sounds like a great solution Andy...otherwise I think he's looking at some sort of fuel related issue, maybe bad gas or high alky/water content?

 

[THALL10326]

There is a dead simple Ignition tester from Stihl (almost all stihl shops have one) that is called a ZAT-4. It runs in-line with your plug and ignition wire. Works great for intermittent failures. Plug it in, run the saw, and you'll soon see if you loose igniton... if you see no flash from the neon, you have no spark..

Good point there Lake. I was thinking the exact samething. I use that tester all the time. I was thinking of suggesting he buy one and use it when his saw acts up but he claims it fires right back up each time it misses so I'm not sure whether the Zat-4 would pin point no spark if he has no spark for a split second. It is one great tool if you have no spark at all. Every saw man should have one of those.

 

[sawinredneck]

Yhank you all!

I apprecitate everything you have done, everyone has gone well above and beyond any of my expectations, Thank you very very much!
The gas I don't see as an issue, not even 2 mos. old it's husky 2 mix and I am running the same in my ms 192t, my husky350, and Shindaiwa brushcutter with no adverse effects on any of them!
I will try and describe it as best I can, maybe I left something out before? The saw ran great, set it down loaded the trailer maybe 20min., picked it back up to drop the other half of the tree, it would not start, I pulled probably 20 times, nothing. Checked the gas, it was low, filled it up, pulled it 3 times, lit right off, idled then died. Fired right back up I tried to goose the throttle it died instantly. Fired right back up, let it idle, it died. Fired right back up, let it idle, goosed it again, died. This went on about five minutes, I finally could "feather" the throttle enough to get it to rev up ran it no load for a minute, just fine. Put it in the tree and had to feather the throttle to get it to rev again and the whole time it "surged" (thats what we always called it a JD) like there was dirt in the carb then it just started to loose power. The surging stopped and it went to the "missing" act, like a 6 cyl running on 4. It was all I could do to get enough power out of it to drop the tree. Brought it home let it set, picked it up the other day, ran fine?
If I am correct, the pulse line should have cleared out an air pocket in the fuel line, right? And it acted just like my dads wildthing when they would vapor lock. I have been around chainsaws and lawn/garden equipment my whole life. Worked on Shindaiwa weedeaters at JD and even rebuilt a Stihl chainsaw at the Heavy equipment shop once (that was a really bad joke!) but this thing baffles me!
Thanks again,
Andy

 

[NoDipNoMore]

New muffler

Hey redneck...drop me a pm in you need a stock "unmolested" muffler for a 039. I have a pair of 039's that I'm willing to part out. One is complete and just needs a piston and the other is a "short block w/carb & muff"

 

[buzz sawyer]

I ran my 390 today with the 25" bar, ran great!!! Then....... I had to drop one tree, it had to fall, forest fire burnt the core and it was going to fall, I just guided it's direction. I cut maybe 1 1/2 cord (3 rick in my neck of the woods) but did not run it out of gas. Went to start it to drop the last tree would not start, for anything, would not start. Filled it up with gas, stgarted right up, then continued to die!!!!! Finally got it to run, but ran like crap the rest of the time!!!!!!! Temp was low 70's with 50% humidity, any thoughts?
Andy

My experience with chainsaw troubleshooting is limited, but I spent 24 years diagnosing automotive problems. It was common to see electrical failures in newer products. I'm wondering if there could be an intermittant short in an ignition circuit. When the saw gets hot, the wire may be little more flexible, allowing the wire to ground somewhere. This could also be affected by the position of the saw.