TM125 stuck on full throttle

[shaughey]

Bought a wee tm racing 125 2 stroke bike. Got a lot of work done to it then It wasnt started in a year and when i started it up it was ticking over nicely then went full throttle by itself. I couldn't get it turned off and stayed at full throttle for about 2 minutes untill it stoped.
Anyone any ideas what could have caused this?? would it have done damage etc??

 

[gary1365]

Would it not turn off with the kill switch. Did you try taking the lead off the plug or stopping the fuel or stalling it. I’d be checking for air leaks and check nothing is sticking in the throttle or carb.

If it’s running lean it’s possible for the plug to get so hot it’ll will run like a diesel with no spark or if there’s too much carbon build up can cause high compression and it can run with no spark.

 

[Mark_C]

Any cracking in the carb boot?

 

[shaughey]

Was more scared of sticking my hand it while it was full throttle. I held in the kill switch but didnt make a difference. I'll pull the carb off and check the boot. Just hoping the piston or cylinder isnt damaged

 

[Apis]

Suggestions above are most likely, but also a leaky crank seal is another possibility. If you still can't sort out with the above suggestions, a leak down test would tell. You can get cheap testers online that do the job pretty well. Ones that read low range. You only want like 5-10 psi for a 2 stroke.