weird 400ex noise

[ny300exrider]

my 400 is making a really weird noise thats worrying me and i dont know what it is. if i start it and keep it revved at a steady pace, every few seconds it clicks and sputters and goes back to the regular rev. when it does it, the carb almost jerks and moves alittle bit like something is jolting in it. the noise is coming from the carb/intake area. i just took the whole carb apart to rejet and didnt find anything out of the normal so i hoped after the rejet it would go away but it didnt. the other day i rode it after letting it idle for awhile and when riding it, i heard no noises, no sputtering and it rode just as usual, just does it at idle when being revved steadily. could the air filter being clogged do this because i know my filter hasnt been cleaned in awhile and it seemed really sticky like there as too much oil on it.

update-i think it has to do something with the carb or choke because it idles ok and seems to rev ok wit it full choked. as soon as i bring it to half choke it revs up by itself and as it slowly revs down the carb jolts and makes a noise. no choke it revs up by itself and then just sputters out. i took it up and down the street and it ran fine until you let off the gas and slowed down

anyone know what could be the problem?

(all stock except white bros air filter, 150 main, 3rd clip on needle, 2.25 on the air screw)

anything is help, thanks

[tater_kamik]

i say clean it, then see if the problem continues

[ny300exrider]

still doing it after filter is cleaned. could a bad spark plug cause the carb to buck and sputter at idle

[ny300exrider]

bump..

[sled_ed 300ex]

man its probly just the jetting , if it backfires in the carb it will make it jerk and stuff so its probly the jetting,if the weather gets cooler you have to rejet the carb and you should set the aire screw every time you leave your house if there has been any change of weather at all.

[ny300exrider]

ok i started it today and when you rev it steady in high rpms its seems to be fine other than the occasional backfire . as soon as you let off and go to lower rpms it backfires alot, carb backfires,and it shuts off. im thinking its something with jetting but i dont know where to start. Or im maybe thinking the spark plug is toast and that is what would cause the backfiring.


stock engine except air filter, 150main,3rd clip on needle, 2.25 turns on air screw, and i dont think i ever changed the pilot but i COULD have a 42 pilot in there. would the 42 pilot cause this if i did have that in there. im pretty sure the noise is backfiring in the carb and intake.

[tater_kamik]

if i remember right, backfiring on deceleration is caused by an lean condition in which it fails to have enough fuel to ignite properly every time. you can fix this by adjusting the idle screw, a/f screw, or if it does it when you upshift, or the backfire is retardedly loud, it could be an exhaust gasket or an exhaust leak.

[AtvMxRider]

rejet the carb

[ny300exrider]

ok now im getting somewhere. what should i do with the idle screw to richen it up because i know it was messed with and its probably way off

[tater_kamik]

a/f screw is really what you need to adjust, once that is good i would adjust the idle

[ny300exrider]

alright sounds good. i will try messing around with the a/f screw.with the idle screw, turing to the right increases idle speed correct?

[Pappy]

are you running an airbox lid or not?

id suspect 2 things.

1) if the lid is on, you maybe a bit over jetted with a stock pipe. even with the lid removed, stock jetting with a stock pipe should be fine.

2) go out 1/2 a turn on the a/f and see if it responds. keep going out 1/2 turn at a time until it either gets worse or better. if going out seems to worsen the problem, you can try going in 1/2 turn. you maybe loading up the engine with fuel with the 150 jet and its merely burbling when you close the throttle.

[ny300exrider]

i tryed it with the lid off as well and it was still doing it. the first thing im going to do is change the plug since it has never been changed and its an 01. second is im going to do what pappy said and go half a turn on the a/f until i notice something.

update-i got a new plug and tryed messing with the a/f and no luck. we went in on the screw a full turn and it seemed to do little, but the little it did seemed to worsen it. tommorow i will work on half turns going out and Hopefully i will see some changes.

im pretty sure its rich because i did a plug check after i got it to run and backfire and it was black.

[ny300exrider]

this frickin sucks i tryed from half a turn out on the a/f all the way to 3.5 and it backfires and sputters off idle.at 3 turns out it ran fine on choke but as soon as you took it off it the carb would backfire and it would sputter out. im beginning to wonder if something is wrong internally thats doing this. i dont know what to do with the idle screw, but whenever i try something it doesnt seem to work at all. the quad wont idle for anything either. it just seems like the symptoms of jetting but i dont know what to do next. should i get that 150 out and go get a 148?

all of this happened after i did a routine oil change i just dont get it. my luck i proabably put the oil filter in backwards and greneaded the whole motor. lets hope not.

[tater_kamik]

i must have been wrong, it is rich if its black as hell... strange how it is only doing that now though, probably an coincidence?

[ny300exrider]

still not running so im gonna bump this up. if the 148 main does not work, what is the next thing i should look at. my dad is thinking about bringing it to the dealer if the 148 doesnt work but id hate to see him get ripped off for something that i could do.

do you think something internal could do this? i would think if something blew in the motor it wouldnt run on choke like it is.

[tater_kamik]

nothing is blown, it is just jetting im sure!! try the new jetting, you could also take it to an dyno to get it dialed in just right...