Stihl 031 AV Idle Racing

[EricSER]

I'm hoping for some second opinions on a saw diagnosis that I've done. I got a Stihl 031AV that has recently had the carb rebuilt and was running successfully but now the saw races at idle even with the idle screw backed all the way out. I am suspecting an air leak but I have no tools to test for this.

I have found that if I sit the saw on the bar/clutch side it will eventually slow the chain down. Once it is sitting normally the chain goes back to spinning. I believe this is indicating a leaking clutch seal? I'm not to terribly experienced in this so I'm hoping that this isn't the case because I don't think its within my ability to replace that.

If anyone has any other ideas to check for or if you need any more information please let me know.

Thank you.

 

[rupedoggy]

 

[CausticUC]

What does your boot look like?

 

[HarleyT]

Check out the fuel line in the tank.

 

[EricSER]

View attachment 745747

Rupedoggy I'm assuming I should be looking under the erratic idle section and it looks like this could be so many different things. I never would have guessed that so many different things could cause this issue.

What does your boot look like?

Forgive me CausticUC if this sounds stupid but are you referring to the spark plug boot?

Check out the fuel line in the tank.

HarleyT I've wanted to replace the fuel line and filter in this saw anyway so I will take a look at it. I'm assuming any break in the lines might cause an issue like this?

 

[CausticUC]

No, the carb to cylinder boot. Easy to not get seated right while reattaching the impulse line.

 

[HarleyT]

After 30+ years, the rubber can get soft/gummy/squishy as well. Also the fuel filter insert usually falls apart and gets sucked into the carb.

 

[EricSER]

No, the carb to cylinder boot. Easy to not get seated right while reattaching the impulse line.

My apologies CausticUC, that was my next thought when you said boot but I wasn't for sure. I will take a look at this once I get home this evening.

 

[EricSER]

After 30+ years, the rubber can get soft/gummy/squishy as well. Also the fuel filter insert usually falls apart and gets sucked into the carb.

HarleyT, Once I get home this evening I will go ahead and replace the fuel line and filter to eliminate that possibility. I just rebuilt the carb on the saw a week or two ago but I will go ahead and open it up again to check for blockages.

 

[HarleyT]

Yeah, the crud clogs up the passage between the screen and the needle on the other side.

 

[EricSER]

Yeah, the crud clogs up the passage between the screen and the needle on the other side.

HarleyT, filter looked a little on the gunky side but the fuel line looked good for the most part. The top was cracked pretty good but I'm not sure if it would have been leaking air or not.

 

[HarleyT]

Cracked?

The pics aren't coming up.

 

[EricSER]

Cracked?

The pics aren't coming up.

Sorry about that! Should be showing now!

 

[HarleyT]

Did you take the filter apart?

 

[HarleyT]

Pull that black cap out and remove the weight.

 

[CausticUC]

If the top of that boot is cracked, you need to replace it.

Waiting on a few of those myself.

 

[EricSER]

No, the carb to cylinder boot. Easy to not get seated right while reattaching the impulse line.

CausticUC, I also checked the intake boot and it looks pretty good for a saw of this age. Its a little dirty but I don't see any cracks at first glance.

 

[HarleyT]

If the top of that boot is cracked, you need to replace it.

Waiting on a few of those myself.

That is the fuel line. Yes, it needs replaced.

 

[CausticUC]

CausticUC, I also checked the intake boot and it looks pretty good for a saw of this age. Its a little dirty but I don't see any cracks at first glance.

Just to double check, you still have the metal ring for the airbox side?

Not cracked is good, sometimes it gets pushed off or out of the airbox when trying to reattached the impulse line behind it.

 

[EricSER]

Pull that black cap out and remove the weight.

I have a replacement filter and fuel line I just got installed. I need to put it back together to test now. I didn't know if the top of the fuel line being cracked like that would produce this issue so I was waiting on putting it back together in case there was anything else that would be easy to check right now with everything removed.

Just to double check, you still have the metal ring for the airbox side?

Not cracked is good, sometimes it gets pushed off or out of the airbox when trying to reattached the impulse line behind it.

Yes, I made sure to hang onto it because I was afraid of losing the little thing! LOL