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Turf-Terminator
11-19-2009, 11:14 AM
I’ve rebuilt a 87 LT250R, new piston & bore and new gaskets. While trying to break the engine in (I would run it for a few minutes and let it cool, I didn’t go right out and crank on it). At an idle the engine started to rev on its own, pretty near full throttle. When I hit the kill switch it remained running, so I pulled off the sparkplug cap, nothing happened. I ended up stalling it by giving it throttle and stalling it. While it was revving steam was blowing out of the overflow tube on the radiator. I am told that this is called “dieseling”. Caused by any engine getting too hot then on its own. Any ideas on why it would rev up and not shut down. I am thinking the reeds may be damaged. I have not opened it up to examine yet… too discouraged.

fx4pitrone
11-19-2009, 02:31 PM
Was the engine leak tested? If there is a leak, it will suck air in and cause an uncontrollable rev... it can be scary!! Does it have fuel? LOL never know, but when running out of fuel, it will lean out and idle high....
When it gets revving like that, the piston is so hot, that even when you kill the spark, the fuel continues to ignite, causing it to continue to run... pull the clutch and kick it in gear w/ brake on....

Chances are an air leak... I would presure test the engine or have it done....

Turf-Terminator
11-19-2009, 06:55 PM
Thanks for the quick answer. I haven’t pressure checked the engine, a friend of mine who had an ‘88 seems to think I’m sucking air between the cylinder and bottom end, (directly below the reeds). If I run a small bead of silicone in this area do you this will hold?

fx4pitrone
11-19-2009, 09:14 PM
My zilla had a leak in that same spot.... Was the gasket replaced?

tommygunnz
11-19-2009, 09:47 PM
One time my buddys 250R had a leak on the intake gasket it was revving high

Quadzilla2win
12-22-2009, 10:04 AM
Yea bud, you got an air leak. your bike is running so hot that it's igniting the gas without spark. So the only way to kill it is to pop the clutch. perform a leakdown test to find the leak and dont start it again until it's fix else you may seize the motor.