really weird backfiring problems

[nosliw]

i'm stumped folks

my 400ex has been backfiring the last couple rides out and seems to fall on it's face right before it does. it does it when i'm in gear and just puting along probably in a gear too high for my purposes. but it doesnt do it all the time, it seemed like on certain areas of the trail it would happen. i downshifted when i probably should have upshifted just to wind it up and see if it did it, nope, dropped rpm and atv speed very well. i put it in nuetral, hit the rev limiter really quick, then went off riding and i think it made it a little better but i'm pretty sure it's all in my head. but before this has been happening i would drop a couple gears at a time and either hammer it or cruise right along with no problems. i checked for looseness of headpipes at head, on there tight. i changed the spark plug, perfect cardboard brown so i'm sure my jetting is good. she's got fresh gas. check tightness of the slip on to headpipe- nice and tight. i cleaned the carb a few weekends ago, shot carb spray through all the jets and cleaned up the float. i know that i did that right because the weekend after that i rode and it was perfect. then a week went by, found a new spot to ride, and it starts backfiring a little. it happened 3-4 times that weekend, then i did the headpipe torque-down and spark plug change and it only did it twice today. just before i got on my computer i backed the fuelscrew out 3 turns from lightly seated, but when i was screwing it in to seat it i think it went about 3 full turns anyway, so i dont think it was in too far or anything, it's got a 42pj also. also the backfiring occurs when i'm barely at 1/4 throttle.

here's some quick specs on the carb

152 main jet
eclip on needle in second position from bottom
42pj (3 turns out from lightly seated)

quad only has a hmf slip on, k&n filter w/ prefilter, stock airbox lid on

the wierd thing is i've had these same mods for about 20-25hours on the quad and absolutely NO falling on it's face or backfiring.

wtf? thanks to all who read it.

HELP!!!

figured i'd get more responses in here :o

[03ChevyX]

You've probably blown a muffler bearing.... or maybe stripped your inverted gerterator... depends on how often you change your blinker fluid, too.

[nosliw]

do you have anything serious to add or are you just apostwhore?

[2004exrider]

what it sounds like to me is that you have it in to high of a gear and you go to give it to much throttle and it cant build up the rpms so the amount of gas entering the cylinder cant be burned properly. try not keeping it to bogged down and keeping the rpms wound a little. i know this because i let someone ride mine and he thought is was in first but was taking off in second, he would take off and then got to punch it and it would start back firing:mad: and then i realized he didnt have it in first. hope that is the solution to your prob, please respond soon and tell me what happened.

[03ChevyX]

Yea, actually i do...

Mine did that too. The voltage from your battery can cause wierd spark timing. Mine did that when my batt went bad. If you havent rode it for a while your batt will be weak and the volts will fluctuate. The Clymer manual talks about it alittle...

[honda426exx]

Dude, I've got the same problem but ive got a white brothers e series with no discs, it runs fine until i let off the throttle and it starts backfiring, i recently bored mine .40 over, port and polished the head and put a stage two cam in it.iI think thats the prob. but i dont know i dont claim to be a mechanic

[2004exrider]

ps. another thing to check is u might have to big a jet, try riding it in first gear pretty slow, then open it up (in a safe place) and if it starts poppin u r gettin to much fuel.

[nosliw]

Originally posted by 2004exrider
what it sounds like to me is that you have it in to high of a gear and you go to give it to much throttle and it cant build up the rpms so the amount of gas entering the cylinder cant be burned properly.


ive been doing it before with no backfiring. my riding style hasnt changed since it was running good

[nosliw]

Originally posted by 03ChevyX
Yea, actually i do...

Mine did that too. The voltage from your battery can cause wierd spark timing. Mine did that when my batt went bad. If you havent rode it for a while your batt will be weak and the volts will fluctuate. The Clymer manual talks about it alittle...

my battery is fine i think, the engine turns over fast. maybe i'll throw it on the charger just so i can rule that out

[nosliw]

Originally posted by 2004exrider
ps. another thing to check is u might have to big a jet, try riding it in first gear pretty slow, then open it up (in a safe place) and if it starts poppin u r gettin to much fuel.

nah, jetting is spot on, i think. i havent changed the jetting, and it was running perfect before all this.

also, i can't reproduce it when i want to. it happens when it wants it to happen for some reason

[2004exrider]

hmmm... not to sure then. have you called a honda mechanic thats probly best bet.

[nosliw]

Originally posted by 2004exrider
hmmm... not to sure then. have you called a honda mechanic thats probly best bet.

trust me they are idiots. 99% of the time i can post the question on here and have it thoroughly answered in no time.

i stopped going to my dealership for help when they told me to run regular automobile synthetic oil in my bike and it's not necessary to rejet a quad with just a highflow filter and exhaust :rolleyes:

[400exrider707]

Originally posted by honda426exx
Dude, I've got the same problem but ive got a white brothers e series with no discs, it runs fine until i let off the throttle and it starts backfiring, i recently bored mine .40 over, port and polished the head and put a stage two cam in it.iI think thats the prob. but i dont know i dont claim to be a mechanic

Need to richen up with the mixture scew bud

[nosliw]

alright well i tore into the carb today and i found that the accelerator pump "boot" that goes over that little metal tube it torn at one end. i went to the dealership and they didnt sell them seperately, i asked how much for the whole accelerator pump assembly and they said $50. no dice. i'm not spending that much cash for a rubber boot.

anyone know where i can buy one seperately? do you think this is why i was backfiring?

[j753301]

i think that boot is just to keep dust out...it doesnt seal anything from air ,i think...

[honda426exx]

Ill try that when me and my buddie check over our bikes for our trip to oklahoma. Thanks for the help. Does anybody know If Little Sahara in oklahoma is good place to ride in the sand. Me and some friends are goin to oklahoma in a week or so and ive never rode in the sand.

[BuB400]

I had the same problem with backfiring, clogged air filter