popping when i let off the throttle

[peckerheadracin]

i just installed a new hmf slop on my 04 400ex. i changed the pilot to a 42 and did not have to change the main i did a wot test to check the main and it is nice and brown did 1/4 throttle test to check the pilot and is also nice and brown. i addjusted the pilot screw in and out to try to get rid of the popping but no change.
my needle is set at the third clip from the bottom do i need to lower it to get rid of the popping? live where the elevation is 4200. please i need a solution fast i only have sat to get it dialed in because i have a race sun.

[Dannys400ex]

check your exhaust for leaks, this usually is the cause for backfiring.

[redrider311]

if you have a fairly old or header there may be a pretty big carbon build up... that caused my old 400 to back fire

[jiggaman2401]

Originally posted by peckerheadracin

my needle is set at the third clip from the bottom

Sorry i dont mean to highjack your thread but i noticed something that i have a ? on. What are the benefits and when should you move this needle?

[zracerx]

I don't know much about adjusting carbs, but popping when you let off the throttle usually means your lean.

[EPDP99]

try to turn your fuel screw out like 1/2 turn and see how that does. The needle controls from 1/4-3/4 throttle.

[cals400ex]

i would try to set the fuel screw 2.5 turns out from lightly seated and fine tune from there. is it just popping when you totally let off the gas?

[cals400ex]

Originally posted by zracerx
I don't know much about adjusting carbs, but popping when you let off the throttle usually means your lean.


in simple terms, raising the needle CLIP will make the air/fuel ratio leaner (less fuel) from approximatly 1/8-3/4 throttle. lowering the clip will make it a tad richer (more fuel).

[EXDUNER127]

First of all you should have changed your jetting after adding that slip on - about 2 sizes bigger, and then you need to lower the clip on your needle... you are running to lean!