Vintage Dirt Bike Q & A

im thinking about replaceing my carb. But i have no idea of the Jets that i would have to buy to make it work correctly. Any comments would be helpful.

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Ride it as if it were brand new

I think more specifics are in order for people to recommend jets. What brand and model of carb are you thinking of buying? Mikuni or Keihin? What size carb? 32, 34, 38? Other things to consider is elevation, air temperature, and humidity.

Your best bet is to buy the carb and a carb tuning manual. If its a Mikuni, I suggest a manual from http://www.sudco.com on carb tuning. They also sell the carbs and jets.

Your MR250 came with a 34mm keihin carb. I would not change the size either way. It came with a 48 pilot and 110 main jet stock. These number do not correspond with mikuni numbers but may let sudco know where to start with mikuni carb jetting. The MR250 was jetted way rich when new. They run much better when leaned out a little. A new mikuni will start easier and run better that the keihin ever could once you figure out the jetting.

http://www.sudco.com also does Keihin stuff. I imagine your bike needs a 34mm PE model. The only challenge I have found is that Honda used special needles with their own coding system. However if you have a factory manual Honda lists the dimensions of the needle (taper, length etc.) and you can use these to make a match with the lists Sudco has.

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