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YZ 250F jumped timing?

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I recently bought a 2008 YZ250F that had a valve break off and ruined the head and piston. Replaced the head and valve train with new OEM, replaced the timing chain and piston as well. I also added a mega bomb header and 4.1 silencer, hot cams, Dyna ignition. After the rebuild the bike started after 2 kicks, and idled perfect. Took it out to do a break in ride, and see how the jetting is. It started and idled just fine again. I started down the road and it seemed to rev up fine and then it just started to studder and wouldn't gain RPM. It almost seems to me like it might have jumped timing. I just happened to have the GoPro running. Have a listen and let me know what you think. I won't have time for a few days to open it up and check the timing.

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OK, start with the easy stuff first. Change the sparkplug, drain the carb and the tank. What I'm looking for it getting any water in the fuel system out. If the tank sat for a month, the fuel could be bad, but I'm sure you probably put fresh gas in. Double check BOTH carb clamps and make sure they are tight. Check the hot start and make sure its seated and moves properly.

Pull the left side cover and flywheel, make sure the stator backing plate is in and tight, and that the stator is not loose and the flywheel is not loose on the hub (look for loose rivits). Since you had the engine out, check all electrical connections and grounds. Disconnect the kill switch and run it again, see if it still does it. Report back.

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sound like your main jet is pluged my kx did the samething after rebuild bike idle fine but when i got to a throttle prostion the rpm would jump

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whatever happened with this?

sounds like a fuel crank or some other issue, it actually sounds like it idles nicely and when you back off the throttle the engine didnt seem to hiccup or jerk or anything which makes me wonder about the mj...

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