backfire

[exracer]

I ride a 425EX and when i back off the throttle it backfires constantly, and i am not sure which way the jetting needs to go.

I dont have much experience in carbs, so any advice would be appreciated!

Thanks,:)

[exracer]

come on guys, someone has an opinion dont they?:(

[ryanh250ex]

i think you would need either to mess around with the pilot jet (go up a size or two) or mess with the fuel/air screws. you're definitely lean, however.


also, what pipe do you have on it? some pipes (eg. my t-4 formy 250) gives off so much airflow that you can never fully rid yourself of the decel backfire.dont know if that happens to the 400 as well though.

hope i helped.


Ryan

[02Yellow400]

No im pretty sure you are rich. And when is it backfiring because your needle controls 0 - 1/8th throttle, the pilot controls 1/8 - 1/4....and your main jet is 1/4 - WOT.

But im sure there are more people on here who know more then i

[DaveEX7]

Well ya know how whenever you start your quad up it idles?

Well that uses alot of fuel when its turned up real high, and that causes a backfire on quads with aftermarket pipes that have a open flow (ex. CT vs. Megamax2).

So turn down your idle a lil bit and see how that works.

[AtvMxRider]

Originally posted by SpeedDemin85
Well ya know how whenever you start your quad up it idles?

Well that uses alot of fuel when its turned up real high, and that causes a backfire on quads with aftermarket pipes that have a open flow (ex. CT vs. Megamax2).

So turn down your idle a lil bit and see how that works.

:huh

[DaveEX7]

Originally posted by AtvMxRider
:huh

Yes, you can turn down your idle....

Some people turn it up when it is cold outside so the engine dont cut out. Its like a cheap rev box.

[ridesa02400EX]

if you odnt know much abut carbs i say you take it to the shop and tell them the altitude you are running at and you need it rejetted and just tell them your mods and stuff and theyll fix it

[DaveEX7]

Originally posted by ridesa02400EX
if you odnt know much abut carbs i say you take it to the shop and tell them the altitude you are running at and you need it rejetted and just tell them your mods and stuff and theyll fix it


Ya and there will be a nice whole in your wallet.......

My friend hadda rejet again, and it cost him about 300, but he got ripped off cause he didnt know what was a good price.

[Guy400]

I asked Hans this from HMF Engineering. He stated that backfiring when off the throttle and decelerating is a function of the air screw. He suggested turning the screw OUT in 1/2 turn increments to see if the problem gets better (or possibly worse).

[Extremeracer167]

its def. rich if its backfiring when u let off the throttle.

[tecate87]

also check for leaks on either the carb boots or exhaust.

[ridesa02400EX]

i got mine rejetted for 90 bucks

[Wheelie]

It sounds like you need to step up the pilot jet one or two sizes, and/or lower the clip on the needle one notch.

It would also be a good idea to check for exhaust leaks.........an exhaust leak can make your quad a flame thrower.

[balla250ex]

Originally posted by ryanh250ex
i think you would need either to mess around with the pilot jet (go up a size or two) or mess with the fuel/air screws. you're definitely lean, however.


also, what pipe do you have on it? some pipes (eg. my t-4 formy 250)


Ryan

I am sure u are talkin about the pro circuit t-4. Is that a good pipe? How does it improve power and sound? Should I buy that or get another type?

[White_Knuckles]

The Procircuit T-4 is a great pipe for the 250EX.

You may need to Dremel out a little material on both the mounts. Take a bit off the top half of the rear mount and the same amount off of the front only bottom half of the hole. Both mounts then can be used without hogging out too much material from one hanger. I got the slip-on 'cause the head pipe is nearly identical and the stock pipe is stainless with a heat shield. Do any filter/air box mods and then perform carb voodoo.

The jetting may be smaller for the main then I've seen here. 98-102 (Keihin) main seems like the right range for me but I have the snorkle opened up, lid on and a UNI. Stock pilot & needle. Air/Fuel screw out 2 turns. 3500 ft.

[DaveEX7]

Originally posted by balla250ex
I am sure u are talkin about the pro circuit t-4. Is that a good pipe? How does it improve power and sound? Should I buy that or get another type?

The T-4 on my friend Bill's quad totally blows ( no offense to other pro circuit users)..... it just makes a bunch of noise, and dont really increase power.

I personally would go with Big Gun again, either that or WB.