Vintage Dirt Bike Q & A

Hey all, I just purchased an 82 250, the first day I got it it ran excellent we were at the sand pits all day and it ran great. I took it out the other night and it started to sputter at high speeds and then it died. I brought it home and it fired right up and I rode around my house once and it sputtered and quit again. I took the Mikuni carb off and cleaned it good, I put it back on and the bike fired up again I was able to rev it a few times and then sputter and quit again, so I cleaned the carb a second time and very thorough and it did the same thing. Please give me any suggestions. I do not know how long the bike sat before I bought it. For the day I rode it I loved it what a nice solid sturdy bike.

Thanx Steve

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"ride and dive"

Had a similar problem once and it turned out to be a clogged fuel tank lid vent line--would run a bit and create a strong enough vacuum to not let gas run down to carb so would sputter out then would sit a few mins and grad release the vacuum and run fine again for just a few mins until created vacuum in tank again--turned out a bit of mud in the end of rubber vent tube on cas cap---just a thought. DOUG

Thanks i'll give er a try!!

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"ride and dive"

you should allso check the tank inside and the fuel petcock and line. make sure everything is clear and clean

thanks guys, Ive checked vent tube tank and petcock and still having problems. I'm lost!

_________________
"ride and dive"

Boy this is fun after a long nights work. I get to think about your motorcycle problems and take some guesses without having to get my hands dirty before bed.

Your bike had a huge workout playing in the sand all day. It just might have been overworked and seized the piston. In some cases when this happens, you could have a glob of melted piston material stuck to the cylinder wall and up the side of the piston that is causing ring sticking issues when the motor warms up and softens everything. You could test this pretty well by taking a cold compression test, then repeating it right after the bike dies - before it cools down. Or, look through the exhaust port and intake port and see if the piston has a big black smear on it.

Or,

You could just have an easy case of a semi-fouled spark plug. A leaky petcock and/or float valve could be passing fuel into the lower end while it sits thereby filling up the crankcase with a puddle of gas. Start it, spin it up, and the super rich puddle will be sent up the transfer ports to douse the spark plug and send you back to the couch for a beer until it dries out. Until the plug dries out that is, and maybe the beer too.

Or,

You could have another ignition issue, like a stator coil that is upset about being wakened from its corroded 20 year nap, that is protesting by cracking the winding and separating as it warms and expands, then reconnecting as it cools and shrinks back into place.

Where is my money? Wait, that's part of the good part - it isn't my money! If it was though, I'd take a look at the plug. If it is dark and gooy, I'd replace it and try it. Failing that, I would take a look inside at the piston sides. finding no issue there, I'd run a cold compression test then arm it up and try it after it dies. If the compression goes up when hot, that's good. If it goes down when hot, that's bad. If all was good to there, I'd suspect that stator coil like a fox with chicken feathers sticking out of its mouth.

Post what you find, as next Thursday late at night I'll hope to learn if I was on the trail or off in the bushes. Enjoy! Jon

Thanks Jon I will try ALL of those things and see what I get and I'll let you know!!

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"ride and dive"