June 5, 2010
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Dear MXA,
    My 2008 Kawasaki KX250F runs bad. It doesn’t want to start and it feels boggy down low. Everyone says that you guys know all the answers about motocross jetting. What should I do?

    We changed everything and we mean everything in our 2008 KX250F’s carb. Here are MXA’s recommended 2008 KX250F jetting specs. The stock jetting is in parentheses.
    Main: 175 (182 stock)
    Pilot: 42 (40 stock)
    Needle: NCYS (NCYU stock)
    Leak jet: 50 (55 stock)
    Clip position: 4th from top (2nd stock)
    Fuel screw: 2-1/2 turns out (1-5/8 stock)
    Notes: To help starting and the low-to-mid transition, we upped the pilot from a 40 to a 42. To help with starting the KX250F, we also added a $179 Boyesen QuickStart accelerator pump doo-hicky. It uses the hot start lever to close off the accelerator pump orifice. This stops excess fuel from squirting into the engine when it is hot. The QuickStart comes with a tunable leak jet, 25% more fuel capacity and a high-volume check valve for consistent fuel metering. It is a bolt-on. It worked like a charm. For more info go to

Boyesen QuickStart.

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