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Backfiring/popping after autocam upgrade & pipe/jetting switch

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I committed a cardinal sin and modified more than one item at the same time. I upgraded to the auto-decompression cam in a 2002 YZ 250F. At the same time switched back to the stock pipe and changed the pilot jet back to stock at 42. The bike now will not idle without the choke. With the choke it runs fine, revs and can actually be ridden in 1st without backfiring. After the choke is pushed in, the bike starts to backfire/pop and sputters out to a stall. The bike ran decent before with an FMF pipe but had a few hanging idle issues and the occasional stall; hence I was switching back to the stock pipe and stock pilot jet.

At this point I'm not sure if I have a carb issue (clogged PJ?), an exhaust leak (I put in new mid-pipe washer and tightened it up well) or messed up timing?

I counted the pins (12) when I put the cam back in and the bike is ride able in first gear with the choke, therefore I think it’s likely a jetting/exhaust issue not timing. Maybe an exhaust leak at the head pipe was created from the flex of switching the pipes.

Does anyone know what the effects of messed up timing would be? I will continue investigating, but appreciate any feedback/experiences.

Thanks,

Ian

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No. I just turned the carb sideways a bit and pulled the bottom off to access the pilot jet. The stock pilot jet was in the tool draw for 6 months and therefore maybe it picked something up and is clogged. I gave it a quick look over and blew it out with low air pressure, but it was late at night and I couldn't make too much noise.

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