2511t surging

[STIHLtimber]

My original and most used 2511t is finally to the point I can't keep it running and I'm down to possibly crank bearings? It's starts and runs but will surge and die on idle. That sound like crank bearings?

Piston and cylinder look good. New tank vent, fuel filter, primer bulb and fuel lines. Carb cleaned with a new kit and air filter is clean. New clutch also

 

[huskihl]

My original and most used 2511t is finally to the point I can't keep it running and I'm down to possibly crank bearings? It's starts and runs but will surge and die on idle. That sound like crank bearings?

Piston and cylinder look good. New tank vent, fuel filter, primer bulb and fuel lines. Carb cleaned with a new kit and air filter is clean. New clutch also

If I was to guess, I would say the plating is worn off the cylinder walls

 

[STIHLtimber]

Not sure if you can tell by this picture? Seems like it has plenty of compression

 

[huskihl]

Yeah that one looks OK still. Not sure what the surging is. Seems like it would have to be fuel related or an air leak or out of tune

 

[Stem]

X2 on fuel related. maybe swap the carb & see if it still surges.

 

[STIHLtimber]

I have a tree service so my fuel is never more than a week old. All the other saws are good including two newer 2511t. I also swapped a carb from one of them and it still surged. All I can think is crank bearing seals but I don't have anything to pressure test with.

 

[Stem]

impulse line? assuming you used OEM parts?

 

[STIHLtimber]

Yeah everything stock. I think the impulse line is part of the intake boot but I could be wrong. I just ordered a mityvac so I can try and narrow it down a little more. Pretty much swapped everything from a brand new saw besides engine and intake boot and nothing has helped it. Right around two years of almost daily use though so it has lasted longer than I expected!

 

[Ketchup]

Can you describe the surging? Wavering idle? Periodically running the chain? Almost dying but pulling back up?

 

[STIHLtimber]

It will idle good far a few seconds then rpms go up fast and dies. To me it seems like it's running out of fuel and a lean issue but I've tried absolutely everything I can think of fuel related. Intake boot and the crank bearing seals are all that's left I feel like!

 

[huskihl]

One other thing nice about them, a whole new shortblock with cylinder and crank is only $160

 

[STIHLtimber]

Definitely a plus! I'll vacuum test this one when the mityvac gets here next week but might be time for a new engine. Hate to know how many hours this saw has on it!

 

[Ketchup]

It will idle good far a few seconds then rpms go up fast and dies. To me it seems like it's running out of fuel and a lean issue but I've tried absolutely everything I can think of fuel related. Intake boot and the crank bearing seals are all that's left I feel like!

Does sound like an air leak. I’ve never seen bad seals on a 2511, but you have to check.

Other stuff to check off just to be sure:
Muffler screen
Air filter
Intake boot ring and white impulse bit
Plug threads
Base gasket
Carb bolt tension

 

[STIHLtimber]

I found the problem today. The intake boot has a metal ring that was missing so the intake to the carb must not have been sealing well enough. The intake boot got pulled off the carb awhile back when the saw got caught in a snap cut.