[HMF backfire] - ATV Riders Forums - Honda, Yamaha, Suzuki, Kawasaki, Polaris, CanAm, Arctic Cat, Kymco ATVs

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HMF backfire
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Posted by: t*wags

To anyone who has a HMF complete exhaust, have you experianced any backfire and how did you resolve the problem fixing it? I've installed the new jets, put the spark arrestor in, and still see no improvement. Anything else that could be done?

Posted by: Scro

When is it backfiring, on decel?

Posted by: t*wags

Yes, it is backfiring on decel.

Posted by: tedwilley

Your jetting is incorrect for your engine setup.
Read the procedures here on how and why to rejet:
www.jetsrus.com
READ the performance FAQ thread by Ryan at the top of this forum.
Buy the jets wherever you want, kit, individually at dealer, etc.
This subject has been discussed repeatedly on this forum. Search for jetting or HMF on the 250ex forum to see the many posts.
Find someone posting the same or similar mods (and at the same general elevation) to get a starting point for the jet sizes.
My advice is to ignore the posts stating they did nothing and everything is fine; that opinion is not applicable to 99% of modded engines.
Backfiring (other than rarely)is NOT okay to leave as is, whether too rich or too lean you will eventually have problems that you will regret not dealing with earlier.
Don't be intimidated, jetting is easy with a few tools and patience.

Posted by: t*wags

Jetting isn't hard for me at all.....

I just put in the jet the factory gave to me and suggested to use for the model.

Posted by: t*wags

Fixed it by adjusting the fuel/air screw.