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Intermittent engine stumbling action!

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Hey guys. I'm new and I have an '89 XR 250 dual sport. It's been a while since I took it out on the dirt, but I ride it around town (San Luis Obispo, CA) every once in a while. Here's my issue:

I noticed that after I hit a small jump or rev the engine too much when I just get on the bike it runs strangely. It runs fine for a little bit, but then it starts to backfire and sputter. Then it will go back to normal. This will continue as long as I am moving forward to keep the engine going. If I stop the engine will die. Do you guys have any insight to this problem? How would the impact from a jump or rough terrain effect the motor like this? Note: it doesn't matter what position my petcock is in.

Thanks in advance...

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Might be a problem with the float and float needle being a little bit plugged up, or not sealing correctly. That would be my first guess, carb is filling up with too much gas causing it to run really rich and sputter.

I would start by pulling off the carb bowl and seeing the the jets are clogged, and maybe remove the float and inspect the float needle. Spray some carb cleaner in there. Also inspect the bottom of the bowl and see if there is a lot of crud/gunk in there. If so, some of that might be getting moved around when you rattle the bike and plugging up a jet or something temporally.

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I agree with zappa about it being float related. Find out what the float drop specs are supposed to be and check them. A common problem is that the carb comes from the factory with the max drop spec set way too much. Allows the float to bounce between stops when riding rough terrain or jumping. The float will displace fuel when that happens, sending it out the overflow tube and forcing it up the jets. Set your minimum drop to the manuals spec then set the max drop 5mm more than that. That should be plenty. That will limit the floats downward travel and prevent the overly rich condition caused by the float bouncing.

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