Chainsaw is high-speed "dieseling"

[RedMF40]

Occasionally when cutting wood at high rpm my saw will go into hyper-drive, very high speed. If it's not max rpm then it's pretty close. Won't shut off with the kill switch. When it happens I use the choke to shut it down. Wait a minute and restart, everything's back to normal. Saw is an Echo 580. Throttle linkage appears to be normal--I've tried jogging the trigger when it gets to over-revving but it has no effect. Anyone experience this, have any ideas what may be going on? Thanks for any thoughts.
Gerrit

 

[Fritz Maurer]

Got an air leak somewhere in the induction system, or more likely a cracked fuel line causing intermittent fuel feed. Whatever the case, it’s leaning way out on occasion.

 

[Fleeter]

Occasionally when cutting wood at high rpm my saw will go into hyper-drive, very high speed. If it's not max rpm then it's pretty close. Won't shut off with the kill switch. When it happens I use the choke to shut it down. Wait a minute and restart, everything's back to normal. Saw is an Echo 580. Throttle linkage appears to be normal--I've tried jogging the trigger when it gets to over-revving but it has no effect. Anyone experience this, have any ideas what may be going on? Thanks for any thoughts.
Gerrit

Had a Poulan 2900 that would run away. It was a bad crankshaft seal.

 

[37chief]

Had a Poulan 2900 that would run away. It was a bad crankshaft seal.

Fleeter may have found the problem. Don't let the saw run at high speed for long, or you will fry the piston and ring, and score the cylinder. Stan

 

[showcrop]

Yes, replace that crank seal before running it again. I was once snowmobiling with my son. I was thinking how my Arctic Cat fan cooled 440 was running really good that day when BANG, a rod came through the front of the case.

 

[RedMF40]

Thanks, will check utoob to see if there's any tutorials. Saw has been pretty trouble-free. Never replaced a chain saw crank seal, so it'll be a new experience. And yes the saw was "running away," not dieseling. Different thing.