Vintage Dirt Bike Q & A

First, thanks to Nathan for registering me to the site.

Second, it's actually my grandson who bought an Elsinore. A 1976 250. I'm not sure if it's a CR, MR, or MT. Probably not the full on racing model though.

Third, my grandson, son and I know next to nothing about two-stroke engines.

The bike, despite having been stored in a barn for several years, starts, idles and runs to approximately half throttle well. At half throttle it picks up rpm until the engine is screaming and won't shut down. Opening the throttle seems to give it a little more speed, shutting the throttle does nothing. All we can do is hit the kill switch. The PO said he went through the carb, and from what I could see he had cleaned it. The slide and needle show no scuffing, main jet looks clear, the needle valve hold pressure when blown through, throttle cable moves easily with no binding. We didn't disassemble the enriching circuit and didn't dig into the idle circuits.

We're stumped. Is there some way other than the carb for a two-stroke to feed fuel to the cylinder? Is there something else we should look for in the carb? Any knowledge or references that can be provided will be greatly appreciated.

Thanks in advance.


DRam

Sounds like an air leak on the inlet manifold or the crank seal behinfd the flywheel

Thanks. We'll check that out.