Vintage Dirt Bike Q & A

i have a 78 cr250 and after driving it for even 10 minutes what happens is when i let off the gas it stays revved up for a little while and if i slow right down and put it back in gear so the revs are low then pull back in the clutch its good again. any ideas what would cause this? is this just the bike being too hot or?? i didnt think so since it doesnt take long......

thanks

You don't provide much information, but I would first check, clean and re-build all the parts of the throttle, cable and carb. It does not take long and it eliminates any mechanical problems that might be keeping the gas "on" when you shut it "off". Then I would go hunting for an air leak; check the carb boot, reed block bolts, any blow-by at the head or base gaskets. Finally I would look behind the rotor to see if there is any evidence air is getting past the right-hand crank seal. The methodical way to check for air leaks is to pull the motor out and have a dealer do a "leak down" test. (I am a little paranoid here because I had two dramatic siezures due to oil seals failing.)

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

sounds like it's running too lean. Raise the needle one groove and turn your mixture in half a turn. good luck

This sounds a lot like what happens when you have an air leak somewhere in the system. The case/ports load up with excess gas under WOT then when the throttle is shut off it keeps running like a partially open throttle because of the air leaks.

The leaks can be almost anywhere in the system: Base gasket, cracked case, case gasket, carb boot, etcetera. The plug would probably read as a lean condition.