I’m stumped

[Bryan Barrow]

I have this chainsaw that really has me stumped. It’s a Stihl 034 AV. I replaced the jug and piston, fuel line, and cleaned the carb a few times. It starts, idles, and revs up well. But when I rev it up, it doesn’t like to go back down to idle. The throttle releases and closes but it’s still acting as if I have the throttle open. What could cause this?


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[Stump Shot]

Sounds like it has a leak somewhere, crank seals, intake boot, impulse line, cylinder base, crankcase gasket etc. are the usual suspects. The best way to find where it is to pressure/vacuum test it. Some soapy water will blow bubbles while under pressure.

 

[Bryan Barrow]

Sounds like it has a leak somewhere, crank seals, intake boot, impulse line, cylinder base, crankcase gasket etc. are the usual suspects. The best way to find where it is to pressure/vacuum test it. Some soapy water will blow bubbles while under pressure.

Oh great [emoji1749]‍[emoji3603][emoji23]


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[drf256]

If it’s idling well, but is slow to come back down to idle, it also can be that your L needle is too lean. An L that’s too lean will make a saw keep revving out of the cut. You’ll hear it “finding” idle after you release the trigger.

Can still be an air leak, but usually the saw won’t idle right if there is one.

Start saw, turn LA until chain moves just a bit at idle. Fatten (open) the L until the rpm start to drop, then back in a bit. Raise LA if you need to.

See what happens.

 

[Al Smith]

A remote possibility could be the annular buffers have degraded allowing the engine to rotate on it's axis in the suspension system which in time will tear the intake boot .You can't tell the boot is torn unless you remove it because the tear will be on the bottom .Been there and done that on an 038 mag .
My goodness you wouldn't believe how fast an engine will rev just going through the idle circuit with a torn intake .Sounded like model air plane engine .

 

[drf256]

Ive got a vid on here of a new OEM seal tearing on an 036. I'll see if I can find it.

 

[fearofpavement]

Is this a repeatable issue? ie, does it start normally, idle normally and cut normally but does this rev thing every time? Or is it more random than that?
Like drf said, if it's an air leak, it probably wouldn't idle normally.

 

[drf256]

Go to 4:17

 

[drf256]

Here's full thread



http://opeforum.com/threads/what-would-make-this-seal-tear-036.7169/

 

[Bryan Barrow]

Is this a repeatable issue? ie, does it start normally, idle normally and cut normally but does this rev thing every time? Or is it more random than that?
Like drf said, if it's an air leak, it probably wouldn't idle normally.

It happens every time


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[RIDE-RED 350r]

I also experienced the torn intake boot on an 038. I couldn't believe how big the rip was given the fact it ran at all!

 

[Duane(Pa)]

A hard yank on a pinched bar is the best recipe for a torn boot...

 

[Bryan Barrow]

A hard yank on a pinched bar is the best recipe for a torn boot...

I’m fixing it for a friend. He let a friend borrow it and it came back needed a new piston and jug (they straight gassed it). I wouldn’t be surprised if they forget to mention that too


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[David Young]

See if the throttle plate is centered well and truly returning to a closed position.

 

[Bryan Barrow]

See if the throttle plate is centered well and truly returning to a closed position.

I did check that an it is. So I’m thinking it’s the intake boot


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