Vintage Dirt Bike Q & A

I just finished my project 1979 CR250 and started it up last for the first time last night. When it fired up, it totally revved out like the throttle was stuck. I shut it down and tried it a couple more times, with the same result. I’m sure I must have screwed something up, I just don’t know what. The throttle seems to be working okay, at least I can hear the carb slide moving when I work it. It has a new flat slide Mikuni on it from Vintage Iron. Any suggestions on what to check would be appreciated.

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Restoring a 1979 CR250R.....

If the throttle slide is not stuck I would suggest you have an air leak - carb boot, base gasket, ignition-side crank seal etc. What did you touch?

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

Basically, I have touched everything. I had a shop tear down the engine so I could have the cases, head and cylinder powder coated. They put it back together with a new gasket and seal set. Boy, I hope it's not something there. That was a lotta work ago....

The carb to reed valve boot is new, so I should be okay there, unless it's not sealing right at the carb.

Would an air leak make it run that fast? The thing is screaming and I have to just shut it down so it doesn't hurt itself. I thought of an air leak somewhere, but I thought (hoped?) it wouldn't make it rev that high.

I think I'll do a little more investigation on the carb. So how do I check to determine if it is an air leak?

Thanks for your help...

Stink

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Restoring a 1979 CR250R.....

Take it to a shop and have them perform a leakdown test on the motor