Stihl MS880 runs at high idle then dies.

[wigglesworth]

ass chain

What exactly is that? Are they hard to file?

 

[RiverRat2]

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!!!!!

 

[gink595]

What exactly is that? Are they hard to file?

Sounds Kinky

 

[Rounder]

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.

 

[Andyshine77]

What exactly is that? Are they hard to file?

Impossible!:msp_lol:

 

[rxe]

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.

 

[chad556]

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?

 

[josh1981]

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

 

[RiverRat2]

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,,,

 

[chad556]

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.

 

[chad556]

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.

 

[mdavlee]

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?

 

[maico490]

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:

 

[RiverRat2]

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.

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...

 

[chad556]

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

 

[mtngun]

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.

 

[hotshot]

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.

 

[chad556]

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.

 

[josh1981]

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??

 

[splitpost]

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.

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