Stihl MS 180C dies in idle

[ahdofu]

Hello,
I have a Stihl MS 180C chainsaw. It starts fine and throttles fine as well. However if I were to leave it in idle, it eventually dies. I tried to increase the idle speed but the idle screw had no effect. In examining the carb, I see that the idle screw is not like a traditional screw that presses against the throttle link. Instead the screw moves in and out of the carb body. I removed the carb and checked the diaphragms as wells as the idle screw. Did not see any issues anywhere, put it back together and the problem still persists. Fuel filter looks good. Short of replacing the fuel line I don't know what else I can do. Anyway has anyone come across this issue and found a solution?
Thanks

 

[Wonkydonkey]

Those saws have them non a justable carbs. although that screw should you mention should slow or increase the revs.
was old fuel left in there for some time ?
Yes you could have a pin hole in the fuel line
Have you looked at the colour of the spark plug,

Maybe there is a slight air leak somewhere (crank seals ?). Have you held the saw at angles while on tickover. Does it change

 

[Maintenance Chief]

Exhaust screen clogged up?

 

[ahdofu]

Fuel is fresh. It is the premixed Stihl fuel and I have never used anything but that. Plug looked OK too and I had already checked the exhaust screen and it was all clear. Yesterday I checked the clutch springs and the chain break and they were OK as well. I have ordered a replacement fuel line so we'll see whether does anything or not.

Wonkeydonkey - I don't think I know how to check for a leaky crank seal. I cannot keep the saw at idle. It just dies in a span of a few seconds.

 

[ahdofu]

Removed the old fuel line and it was in pristine condition. Did a vacuum test and it was negative. Not knowing what else to do I replaced both of the diaphragms in the carb. That did it. All in order now. The idle screw is also functional now. Although both diaphragms were flexible, I guess one of them must have been borderline.