Engine over reving

[petersenj20]

Sometimes the engine runs wide open full rev without touching the throttle. The only way to stop it is to upshift. Turning the switch off will not kill it at this point. Get the engine slowed down, the switch will work.

It has a new piston and reed valve. It did the same thing before the new parts.

This has become very dangerous at times like when coming down a steep decent when trying to slow down and upshifting is not a solution.

My first thought was the reed valve, but it checks out ok. I have worked on lots of 2 strokes but never had this problem.

Any advice?

 

[tumblingtwerp9]

air leak? did you do a leak down test?

 

[sicivicdude]

You have a massive airleak and possibly a defective handlebar switch.

A leakdown tester should diagnose the air leak and allow you to find it, a multimeter will find the weak link in your "kill" system.

 

[Blaaster]

Remove the exhaust pipe, block off the port , remove the carb and apply 7 psi to the carb boot. It should hold for 5 mins. Member slickerthanyou can help you out with a tester.

 

[BlasterIan]

Definitely an airleak, see this all the top when messing around with top end builds.

 

[Blaner]

Also have a look at the Throttel over ide system. what year is your bike?

Leak tester DIY: http://www.blasterforum.com/do-yourself-20/build-use-leakdown-tester-10663/

TORS DIY: http://www.blasterforum.com/do-yourself-20/how-remove-your-tors-655/

 

[Larry's Shee]

Check that the slide, cable, and thumb throttle all work smoothly. Check for air leaks. Might be a problem with the switch, but most likely it is auto-ignition, wherein a lean condition causes a hot-spot on piston or head. Then it's game on, you have to either kill fuel, air or mechanically overpower the engine, higher gear, clutch out, brake on.

 

[dbowhntr]

Check that the slide, cable, and thumb throttle all work smoothly. Check for air leaks. Might be a problem with the switch, but most likely it is auto-ignition, wherein a lean condition causes a hot-spot on piston or head. Then it's game on, you have to either kill fuel, air or mechanically overpower the engine, higher gear, clutch out, brake on.

Yup, just like a runaway diesel at that point. Scary!