Help Please! stihl ms170 chainsaw problem!

[lejardinsecret]

Can someone help please?
I have a stihl ms170 chainsaw which has been reliable for a couple of years. It has however developed a problem in that it starts fine after a few tugs, however it only runs at full revs and the throttle has no effect!
I have taken off the air filter and the physical connections at the back seem ok. The throttle seems to work when the choke and the safety are on.
Any ideas? clutch?
Any help would be greatly appreciated,
Thanks in advance,
Paul

 

[Mange]

It sounds as it want a bit more gas, since I Stihl am not very interested in the still saws, I think others can help better.

 

[Lobo]

Paul, I guess starting from the basics may be required here.

If you stored your saw for a few months with gas in it or if not properly fully drained this old gas may have created a sticky substance inside the carburetor which is causing the winding of the saw up completely. Just to eliminate this aspect have you or can you run carburetor cleaner in it. Companies such as Briggs & Stratton and others retail such products or you can purchase it in an auto parts store.

 

[Fish]

Remove the screen out of the muffler and see if it runs better, if so, clean your air filter.

 

[lejardinsecret]

Thankyou for your interest gentlemen.......
Far from sitting around for months it has been used most days over the winter.
I have checked and cleaned spark screen of the muffler, cleaned air filter. It runs great...but at full throttle, with the chain running from start up, unless the safety is on. Tried turning back LD screw to no effect.
Until yesterday it was fine, now idle speed doesn't exist!
My thoughts were there is an air leak into the carb somehow. Lobo's advice is something I hadn't considered... the muffler was filthy.
before I go chasing some carb cleaner, which believe me in France will be a major mission, lots of shrugging and sucking teeth!! does anyone else agree with this plan of action?

There is a small white plastic washer? behind the carb..... I examined it today and it seems a bit "warped" could this be the prob also?
I look forward to your thoughts,
Regards
Paul

 

[stihltech]

hoses

Pulse hose or fuel hose, intake boot maybe.

 

[Fish]

That little ring is usually warped and is a problem area with this saw. Leave it out, and clean out your carb while you have it off.
Your initial description is a little confusing. The throttle seems to work when the choke and saftey is on? It only runs at full revs? And the throttle has no effect?

 

[lejardinsecret]

[QUOTE=Fish]That little ring is usually warped and is a problem area with this saw. Leave it out, and clean out your carb while you have it off.
Your initial description is a little confusing. The throttle seems to work when the choke and saftey is on? It only runs at full revs? And the throttle has no effect?[/QUOTE]

Yep i was/am a little confused!!
It runs flat out and if I press the throttle you can hear a sound change but it is going flat out anyway.....no change in speed.
When on warm start, when throttle pressed moves to run position......hope thats clearer!!
Starts with chain running flat out unless safety brake is on.

So the ring is not required? what exactly is it?

Thanks for your interest!
Regards,
Paul

 

[njforestfire]

Sounds like an air leak to me. Check the rubber boot between the carb and the cylinder.

 

[Crofter]

This is a rare happening, but have you checked that the throttle flap has not disappeared off the throttle shaft.

 

[Kneejerk Bombas]

The sound wouldn't change when he hit the throttle if it were a missing throttle plate. Sounds like some kind of air leak.

 

[Crofter]

If it is sucking enough air to achieve wide open throttle condition, where is it getting the fuel to go with it? I know that an air leak will give an exceptionally high idle that cant be lowered by backing out the throttle stop.

 

[Fish]

I have left the little ring off before with no problem. Look at the throttle shaft and see
if the screw that holds the throttle plate in place is still there. If it looks ok, for saftey's sake, remove the bar and chain, start the saw, and with a can of wd-40 with
a straw, spray around the base of the carb, boot, etc. If you hit an air leak, it will slow the saw down. It sounds more like a throttle plate problem though.

 

[lejardinsecret]

Thanks for all the advise, I'll have another look today and check out the various ideas. I did check throttle assembly first off, but I might have missed something! haven't looked at the boot which could be a likely culprit.
I'll let you know how it goes,
cheers,
Paul

 

[lejardinsecret]

Yep Fish you were right, took me 2 minutes and its back in action, I'll pick up a new ring when I get the chance.
Thanks to all for your interest,
Cheers,
Paul