BACKFIRING Rich ir Lean HELP

[OTLEYEX]

03 400ex 42 pilot 170 main full HMF system airbox lid on. 2 1/2 turns out on mix.

A decent amount of bachfire on decel. Is it rich or too lean?

[Jonesy]

backfire is too lean, try going out more on your mixture screw. try about 3 1/2

[prepracing]

Actually it could be either rich or lean....... that 170 is awful big for it to be lean. I would do a plug check

[OTLEYEX]

Ok, I checked it is a 180 main 42 pilot. Backfires with the airbox lid on or off. Does the 400ex have exhaust gaskets for the header? Just curious I did not see any when I removed the stock header?

[GOTFEAR]

Stock 400 with pipe should be around 145 to 155 with the lid on and chang the plug

[prepracing]

Originally posted by OTLEYEX
Ok, I checked it is a 180 main 42 pilot. Backfires with the airbox lid on or off. Does the 400ex have exhaust gaskets for the header? Just curious I did not see any when I removed the stock header?

yes they have copper crush gaskets, they usually stick in the ports when the pipe is removed. And they do sometimes leak and cause backfiring when pipe is put back on. Man that 180 main jet sounds huge.....but I have never rode in Iowa so it may be ok out there :confused:

[cals400ex]

make sure you do not have an exhaust leak at the head or at the header/silencer connection. check the carb boots and make sure you don't have a crack or an air leak. they need to be on tight. i would not run larger than a keihin 160 main if it was me.

[fitethesystom]

I know how much you guys may hate fel injection, but in my experiences with engines with carb vs. fuel injection the carb sends me off the cliff. Alot of my bad experiences were on smaller engines and outboards. That's just me though!:blah:

But yeah, it could be a leak. I would double check all that.

[alaskin 450R]

the stock main jet is 148, check to see if you ahve an ehaust leak somewere and that 180 might be a little to big try a 170