Backfiring on deceleration

[MR.BIG]

I have a 04 450r with the hrc kit, pipe, and filter. I has ran great but just recently in started to backfire when I am going down a hill or slowing down. It never did this before so I am thinking it must be running lean. If I adjust the air screw do you think it would help and if so I would have to turn it or out. If not I guess I will have to change the pilot jet but it just started happening so it's kind of confusing.

[MadMan400ex]

you sound correct in guessing that its running lean. my guess is that the packing in the silencer is burning out (normal wear) and you could fix this problem by changing the jet one size at a time till the problem goes away or you can repack the silencer. neither is very difficult unless you are guessing at the size jet you need. then it can take a long time. you didn't state what your plug looks like, but that will be a tell-tell sign of what your engine needs.

[Lance F]

Sounds like you might have an exhaust leak. Check your header. Check the bolts that connect the header to the head.

[Trevor]

My 300 dose the same thing.

[MR.BIG]

Originally posted by MadMan400ex
you sound correct in guessing that its running lean. my guess is that the packing in the silencer is burning out (normal wear) and you could fix this problem by changing the jet one size at a time till the problem goes away or you can repack the silencer. neither is very difficult unless you are guessing at the size jet you need. then it can take a long time. you didn't state what your plug looks like, but that will be a tell-tell sign of what your engine needs.

The plug is a light tan color. The bike runs excellent otherwise. It just pops and sounds like crap if I go down a hill and let off the gas. The packing does sound like it could be the problem otherwise I will have to jet richer on the pilot jet a couple of sizes.
Thanks everyone for the info!

[cals400ex]

turn the fuel screw on the bottom of the carb out a 1/2 turn.

[Sjorge450R]

the back fireing is caused by a lack of back pressure... when my 300 ex was doing that, i called supertrapp up and they told me to take out a disc or two, so in your case it sounds like it has to be the packing, because like you said, it didnt do it before.

[MR.BIG]

Thanks guys I will repack and see what happens.

[86-250Rnut]

Might be a bad cam.
Mitch:macho

[trx400exxracer]

your probably not jetted right you might be lean

[Yee-Haw_400EX]

Originally posted by 86-250Rnut
Might be a bad cam.
Mitch:macho

Yeah, I bet his cam went bad.


ROTFLMGDFAO!!!:p :p :p

[Sleeper]

I vote lean.



sleeper

[tater_kamik]

repack to see if it goes away, but you could go ahead and change your a/f and it should fix it. make sure you dont have an exhaust leak, but i doubt you do.

[Yee-Haw_400EX]

Check the air in your tires. That's what caused my backfiring.

[Honda TRX250ex]

mine backfires and the header is tight and its not to rich its just the exhaust

[WyteKraka]

for sum reason when i start gettin low on gas, my 400ex will start to backfire. fill it up and its fine.

[adrenaline]

bad cam? no lol
running lean yes!

did you just put the pipe on?
weather is changing so the jets will need adjusting
or try to come out 1/2 a turn on the carb.

i would say jetting i just put a new pipe on my quad and it pops during deceleration its running lean im 100% on that
i just put a Nmotion on my yfz and picking up my jets tomorrow.

plus after jetting you'll get more power:devil:


lol the tire pressure does make a huge impact on it thought hes right too little air makes it run so lean fill them rock hard you'll gain 35hp to the ground!! yikes (for you newbs that is a joke)

[the Z Man]

EXHAUST LEAK!!!!!!!

[CD400EX]

My 400EX started doing the same thing since the weather got colder. Where is this fuel screw? How do I re-jet the carb and where do I get jets?

[MR.BIG]

Originally posted by CD400EX
My 400EX started doing the same thing since the weather got colder. Where is this fuel screw? How do I re-jet the carb and where do I get jets?

I repacked my silencer and it still did it so i started adusting the fuel\air screw and it helped it alot.
There are only 2 adjustments on the 400ex carb idle and fuel-air screw. Trying turning the screw out about 1/2 turn and go from there. You have to remove the bowl to get to the jets. There is a main jet and pilot jet. Any atv place has them but try to air screw first.

[adrenaline]

yeah if you have a pipe and a air filter (aftermarket) then its going to pop if not jetted right...or the air/fuel screw isnt out enough..remember new air filter your allowing more air in and exhaust is letting more out but the carb is still set up the way it was stock so you have to adjust accordingly

[Jersey450R]

leaner is meaner :p

[QuadJunkies]

Originally posted by Lance F
Sounds like you might have an exhaust leak. Check your header. I just had that happen on mine!

[ill_lil_romey]

An exhaust leak, a loose air boot, or carb can be your problem. They all lead to lean conditions in the mixture. Try looking into that first, and if all of that seems to be fine, then you need to richen the mixture.

[wboy62417]

mine did the same thing once i just went a size up on my jets but lance is right it could be an exhaust leak but if you ruled that out i would go with the jets

[Yee-Haw_400EX]

I've been riding my 400EX like that for 5 years but oh well.

I still think your cam probably needs to be rebuilt.:rolleyes:

[parkers30]

Originally posted by Honda TRX250ex
mine backfires and the header is tight and its not to rich its just the exhaust

just because the header is tight doesn not mean you don't have a leak, if you did not replace the exhaust crush gasket when you took off the pipe or put it on in the first place, its very possible you have a leak at the head, which will cause a nasty backfire

[QuadJunkies]

Originally posted by parkers30
just because the header is tight doesn not mean you don't have a leak, if you did not replace the exhaust crush gasket when you took off the pipe or put it on in the first place, its very possible you have a leak at the head, which will cause a nasty backfire

[jon Good]

Check your pilot jet you might need to step up the size one or two sizes. on my 400ex i went from a 45 to a 48

[pteknique]

It's the air screw adj.

my 400ex back fires all the time and nuthin is loose and the plug is nice n tan . and every one is saying lean can cause backfiring. well rich can too cuz a while ago my jetting was rich and that thing would back fire like 2 times every second if i could keep it running.

[Honda TRX250ex]

Originally posted by blue450yo
my 400ex back fires all the time and nuthin is loose and the plug is nice n tan . and every one is saying lean can cause backfiring. well rich can too cuz a while ago my jetting was rich and that thing would back fire like 2 times every second if i could keep it running.
theres alot of chit wrong with you quad, and quads arent sppose to back fire...

well i here alot of back firing at the races. and my engine is getting fixed right now and the only nown problum right now is needs engiine seals and a clutch basket.