Stihl MS170 bogging down

[Larry D]

This thing is killing me. I have a Stihl MS170. Recently it started bogging down when I would put any pressure on it. The carb was replaced. Still does it. If I get the chain up to speed and put it on the wood, it cuts nicely... until I put any pressure on it. There is also smoke coming from around the clutch, even if the chain is spinning, but not cutting into wood. I have taken it apart, and cleaned the clutch surfaces. Now, if the clutch was smoking, the chain stopped in some wood and the engine was still revving, I would say it was the clutch slipping. But the engine bogs and even stalls. Carb has been adjusted but it is no better.

Thoughts?

 

[user 122190]

Could be the muffler is clogged. Take if off, and give it a good a scrubbing, and inspect the piston and rings while you are at it.

The clutch shoes will have a bluish look to them, if it has been over heating/smoking.

 

[HarleyT]

Let us see some pics!!

Pics of the clutch area, pics of the chain, pics of the sprocket , bar, etc...

 

[Larry D]

Could be the muffler is clogged. Take if off, and give it a good a scrubbing, and inspect the piston and rings while you are at it.

The clutch shoes will have a bluish look to them, if it has been over heating/smoking.

Muffler was checked and clear.

 

[Bob Hedgecutter]

Muffler was checked and clear.

More importantly the muffler spark screen was checked and clear?
If the clutch is heating enough to smoke, I wonder what kind of condition the surrounding plastic case and the crank oil seals are in?
When the muffler was off, did you check the condition of the piston/ring on the exhaust port side as MontanaResident suggested?

 

[Intotheether]

Had a somewhat similar issue with a MS180

Turned out to be that the spark plug gap had opened past spec. Tapped it back down to spec, and it came alive again.

Also make sure your bar sprocket is freely turning and well lubed. Had a bar get pinched in a tree and the sprocket got the worst of it.

 

[Larry D]

Had a somewhat similar issue with a MS180

Turned out to be that the spark plug gap had opened past spec. Tapped it back down to spec, and it came alive again.

Also make sure your bar sprocket is freely turning and well lubed. Had a bar get pinched in a tree and the sprocket got the worst of it.

Interesting. Any idea what the correct gap is supposed to be?

 

[Intotheether]

Interesting. Any idea what the correct gap is supposed to be?

Its in your owners manual in the tech specs. Stihl has all their manuals online for free download if you don't have a paper copy.

 

[HarleyT]

Let us see some pics.

The carb doesn't have much in the way of adjustments...

 

[Larry D]

Checked the plug gap. Perfect. Still can't figure this out. Arg . Looked at the piston and rings. They all look to be ok. No scoring or anything like that. Here are a couple pix of the piston and the clutch. Maybe my fuel mix is off? I don't think it is. But maybe I'll mix up a new batch and see what happens

 

[Sam R]

Is your chain nice and sharp?
Bogging in the cut suggests a lean running condition. If you have a tachometer - can you say how far it revs up unloaded? I believe spec for the 170 is around 13k. The hi speed jet in the carb for those can be changed to a larger or smaller one if it's running lean or rich.
If you warm it up, put it in some wood and let it bog down, immediately pull the plug (it will be very hot) and snap a pic of that. Could tell a lot.

 

[L34]

+1 with Harley,does it have mixture screws or just the air screw?

 

[Larry D]

Just the air screw

 

[HarleyT]

Let us see a pic of the sprocket teeth and chain, show the bottom of the chain, that engages the sprocket.

 

[L34]

Same as ms180 I am working on.
Can't tune.
Going to fit a Walbro.

 

[L34]

Fitted the chi walbro,different saw all together now I can tune it.

 

[Bob Hedgecutter]

Just as a matter of interest- anyone having more than a casual play with one of these saws and getting in deep enough to remove cylinders/manifolds= just be aware of the way these saws impulse. There is a rubber nipple that lines up with a hole in the casting at the intake side. Get the fitment wrong and the nipple can be closed over when the manifold is fitted and/or if you try to slide the cylinder in while the manifold is in place.
If it does not line up, the impulse will not work, saw may fire up on choke- but wont run WOT.