Stihl 028 AV Super: idling very high

[monaco]

I recently replaced a buffer bolt and fixed the ground kill switch wire on this saw, now it starts and runs fine, but it idles high, almost full throttle. (I did not do any carb adjustments.)

I visually checked the idle screw and it's not keeping the throttle open.

It ran fine before this bolt fell out.

Anyone know why it would be idling so high?

 

[pioneerguy600]

It must have an air leak, check the intake bellows for a crack as it might have gotten stretched out when working on the rear AV mount.

 

[Wood Doctor]

It must have an air leak, check the intake bellows for a crack as it might have gotten stretched out when working on the rear AV mount.

So, you are referring to what some of the IPL's call the intake manifold or boot? The old 028 service manual also calls this simply an elbow. A crack in one of these would be a prime source for an air leak that would lean out the fuel mixture.

 

[monaco]

I've been able to find a part called a boot, but not a "bellows"

 

[Wood Doctor]

I've been able to find a part called a boot, but not a "bellows"

Agreed. And, if that is the problem, it's kind of a bear to replace them. You have little room to work with. The carb must be removed to get to the intake throat of the boot and a hose clamp surrounds the portion that connects to the cylinder. You might be able to do this without removing either the cylinder or the tank housing, but that's not easy.

I recall replacing the impulse hose on an 038, and I had to remove either the tank housing or the cylinder. I went with the tank housing. Took me most of a day to do it.

 

[monaco]

I haven't looked yet, but if I can place eyes on a bootcrack, I'm putting high-temp fireplace silicone on it

 

[SEAM]

I would check the impulse hose...
Have the saw run and spray some oil (WD 40 etc.) between the engine and carb box. If the engine speed drops or the engine stalls you got an air leak around there (intake boot or impulse line)...

The impulse hose can be replaced with long nosed pliers after removing the carb...

 

[JonCraig]

I visually checked the idle screw and it's not keeping the throttle open.

To clarify, the throttle shaft is or is not sitting on the idle stop screw?

If it is, then suspect air leak as others have mentioned.

If the throttle is NOT sitting against the idle screw, inspect throttle linkage to ensure it's not in a bind, etc.

 

[62alf]

X2 on the impulse hose. I just fixed one up for my son and the hose was bad...