horrible backfire

[flattrack450]

i've got a 40mm mikuni. when i rev the machine toward the rev limiter in 3/4th gear and then let the motor wind itself back down, i immediately get a horrible, sharp backfire... at least 4/5 pops before the deceleration has me slowed back down.

right now running 2nd most lean needle clip and 170 main.

generally speaking, where should i turn first?

thanks

[hondarider2006]

Your mj sounds good, how about your air/mixture-idle screw??

[flattrack450]

just went out for another run. needle to the 2nd richest setting, main up to 180. still backfires. flames shooting out the exhaust pipe at every pop!

any other ideas?

[cals400ex]

i would try richening up the pilot jet/air skrew.

[Hotdog]

my buddies quad was doing the same thing. We put in a bigger pilot and it fixed the problem.

[44oEX]

yeah it's the pilot or the air screw. it has nothing to do with the main or the needle.

Does the carb have a fuel pump on it??

I didn't know Mikuni made ANY type of carb for the 400ex...:confused:

[chad502ex]

Well, I'd be more concern about your valves not seating properly and allowing the backfire to occur on engine breaking.

My point is, I'd pull the head and lap or grind my valves to my valve seats if I were you.

hope this helps.

Chad502ex.com

[ewalker302]

I'd say go up a couple sizes on the pilot first.

:bandit: