Stihl 08 won't rev

[WoodRipper]

My friend has a Stihl 08. It starts but won't rev up to top end rpm's. I did a carb. rebuild - no difference. We put a brand new carb. on it - no difference. The rev. limiter is not the problem, since I disconnected it and it still won't rev up. Could there be something with the ignition system that could cause this? Other ideas? Help - this is driving us both nuts. Thanks.

John

 

[axlr8]

Did you check the throttle linkage? clearance issues?

 

[WoodRipper]

Did you check the throttle linkage? clearance issues?

Yeah, the throttle is free and opens fully.

John

 

[1Alpha1]

Partially plugged muffler?

 

[buzz sawyer]

That saw has an air vane governor so it won't over rev. Make sure all the linkage is operating freely and tune it in the cut under a load.

 

[WoodRipper]

Partially plugged muffler?

Nope, we checked that early on.

John

 

[WoodRipper]

That saw has an air vane governor so it won't over rev. Make sure all the linkage is operating freely and tune it in the cut under a load.

I verified the air vane's not the cause by disconnecting the linkage between it and the carb. No difference. We even put a new carb. on it. No difference. There's no point in trying to tune it under load because it doesn't rev up - at all. If you put it in wood, it stalls. I don't know what the rpm's are but I doubt it's even 1000.

Keep those ideas coming. It has to be something. Thanks.

John

 

[XSKIER]

Breaker point gap ok?
Condenser ok?
Ignition coil ok?
Ignition timing ok?
You should have a strong spark that will jump at least a 3/8" gap at cranking speed.

 

[nitro]

fuel filter on the end of the fuel line clogged with ethanol crud???

happened to me....

 

[sefh3]

I would look really close at the points. If the condensor is failing it would reduce spark and cause you engine not to rev. I would clean the point and regap.

 

[Adirondackstihl]

Check the intake manifold for something partially blocking the impulse passage....ie....the gasket or old krud. Maybe not enough impulse pressure to pump enough fuel through the system.

opcorn:

 

[Nardoo]

My money is on timing. Pull the flywheel and check if the key is still there. I have seen them assembled without the key and then the flywheel slips a little on tightening and retards the ignition. Is it slow to accelerate and get hot?
Just my thoughts.


Al.

 

[WoodRipper]

Thanks for the additional ideas. It's not fuel related as we've been over that at least 3 times all the way from the tank. We've also verified there's nothing clogging the gasket and crankcase opening that provides the pulse to the carb. I think the comments about the ignition system being the culprit is probably the most likely cause now. We haven't had the flywheel off yet - I guess it's time to take a look at what's going on under there. Any words of caution? I assume the flywheel side is a normal, right hand thread, yes?

Thanks,

John

 

[Adirondackstihl]

Right hand thread.....yes

 

[GrassGuerilla]

opcorn:

 

[Fish]

So when you disconnect the air vane, have you wired it both ways, open and closed???

 

[WoodRipper]

So when you disconnect the air vane, have you wired it both ways, open and closed???

At first we did nothing. Then when I realized what it was and how it might be the source of the problem, I disconnected it and made sure the return spring didn't close the choke plate. I didn't try it with the choke plate closed; just didn't see any reason to think that would help. Mind you, we've had two carbs. on the saw now, and run both with the air vane connected and disconnected with no change. My friend actually has two 08's and we swapped out the new carb and put onto his other saw and it ran fine. So the carb itself can't be the issue.

Thanks.

John

 

[Fish]

Well disconnected from the vane, what is in place to ensure that the choke is staying open?

 

[WoodRipper]

Well disconnected from the vane, what is in place to ensure that the choke is staying open?

Nothing, but there was nothing to cause it to close either, and with the air screen removed you can just look in the end of the carb to confirm the choke is open. It was.

John

 

[Fish]

OK, your next test... Drain the fuel out, start and run it and describe what happens when you run out of fuel.....