Popping BAD when cold....

3 replies to this topic
  • kizzle426

Posted December 05, 2005 - 12:55 PM


Okay, aside from the leaking fork seal (which i can't afford to fix, and there was no dirt), I got my new (3rd) decomp lever in today and started the bike for the first time since I endoed it (reason for leaky fork seal and broken decomp lever) and it was rough. Took a while for it to start. Once it fired it FIRED. Meaning, backfiring really badly. I was atrributing this to the fact that I crashed it, left it sitting for two weeks, and it's 50 outside, when it's normally 75 plus when I ride. Once it warmed up, it idled fairly smoothly with no pops unless a real good twist was given, though it still wasn't totally warm. The only thing that was wierd was that when I revved it, it hesitated to idle. Is all this just temperature stuff? I moved the clip up a notch on the needle a while back because I was fouling plugs, should I take it down now that it's cooler outside? Keep in mind this is my first MX four-stroke and I'm still kind of a virgin to all of this. Thanks

  • shanedut

Posted December 05, 2005 - 01:46 PM


It sounds too me like you need to turn your fuel screw out or your pilot jet might need to be richened up. My 426 pops when its cold till its warmed up and once its warmed up it idles and runs fine. The popping can come from jetting issues or from a leaky exhaust either at the head or where the headpipe and the muffler connect. If you havent done it already i would buy a zip ty fuel screw for fast adjustments. Here in CO in the morning i'll set it for that temp and I find after it warms up i have to lean it out a little to get it running good. As for your fork seal you can do it yourself for about 30 bucks or less.

If you dont know too much about jetting i would look at this site it explains jetting pretty well


Here is a good website for re-doing your forks and other information http://www.thumperfa.../fork_seals.htm
this is a 250f sight but there is also good information on it

Hope this helps

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  • Matt96xr6

Posted December 05, 2005 - 05:52 PM


Your hot start is stuck in the carb bore. Take it out, clean it and the bore, then put a light coat of grease on the plunger.

  • mose29

Posted December 05, 2005 - 08:16 PM


The same thing happens to me with any temp change.I got the adj.fuel screw and use it often.It works...

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