Weird sound, help!

[EXDUNER127]

My bike was running way lean last weekend, to where it kept back firing, so i took it home and put a better jet in, changed the oil, emptied the old gas and put new fuel in. I then went to start this weekend and it wouldnt start, so i took the carb off, took it apart and cleaned it with carb cleaner, then tried to start it and it didnt want to start, but if we sprayed carb cleaner in the carb it would fire right up. We then figured it wont stay idle, and we messed with the throttle cable and the only way it would idle would be when it was reving high but then this weird pap sound would come out of the carb and filter every other second, like a back fire through the filter instead of pipe. could this all be because of i still have the stock pilot jet which is a 38 pilot and it is starting to get cooler the needle is in the right position....Should i get a richer needle like the one that comes with dyno jet, could the pilot have that effect on the bike to run it lean, i have a full pipe, k&n, no choke and no motor work yet. It has been lean for some quite some time now but never enough to be bad, it just got way lean since the weather changed..

Heeeeeelp!!!!

[zephead400ex]

:huh...backfiring through the air filter? Doesnt make sense...reverse air flow??? Do you mean you put a bigger main jet in? what size?

[EXDUNER127]

I went from a 168 to a 172, but i am curious if i need to bump the pilot jet up to a 40 or 42, and i dont know where the air fuel mixture screw should be....

And yah, there is a weird back fire from the filter you can see it sucking from the outerwears and then you see here the sound and see the sucking stop at that time, just for the sound!
I turned it off right away cause i didnt want to break anything...
I am freaked!

[EXDUNER127]

BUMP!

[zephead400ex]

That jet size seem a little big. All you have is an aftermarket exhaust and installed K&N filter w/ the motor all stock? To me 172 sounds way big, have you tried to drop your needle a notch or two? Did it run ok with the 168 in? You might want to go to a 40 or 42 pilot, that would help idle.

So it actually doesnt "backfire" through the air filter? Right?

[michigan rider]

if it is backfireing into the carb and filter it sounds like you could possible have a bad intake valve

[member]

yea in auto class we hade the same prob with a lawn mower, i kept backfiring out of the airfilter, it turned out that the compressin realase was stuck open... so that could be a bad intake valve good luck fixin it

[EXDUNER127]

Is that the only thing it could be?
That jet size isnt big for where i live, the elevation is 4000ft....
Will the new pilot jet help the bike start better? How bad is a messed up intake valve?

[EXDUNER127]

1200ft i mean.....

[toby400ex]

Are u sure its actually backfiring through the filter, cuz when i foul plugs it will pop a couple times when the plug is wet, look at the plug. U could have fouled it by being way too rich.

DUDE!!!! i knoe exactly what ur talking about. Mine does it to but only when i first start it up if i barely rev it, it like cuts out and the carb makes a noise kinda wierd to explain. Like the slide is poping back but thats not it. It sounds like when u "Click" ur tounge off of the roof of ur mouth but not as loud. But once it warms up it stops but it doesnt hender performance so im okay but i thought id just tell u.

[Toadz400]

Originally posted by zephead400ex
:huh...backfiring through the air filter? Doesnt make sense...reverse air flow??? Do you mean you put a bigger main jet in? what size?

yea, the same thing happened to me this summer when i first got my EX. the jetting was set up for winter so it was too rich, and when i would first start it up it would actually sound like it was backfiring through the airfilter, making a really weird sound. so i'd shut it off and run inside screaming like a little school girl...haha...not really, but i had my friend come over and we adjusted the valves and rejetted and it ran perfectly, purred like a huge cat on steroids:)


DUDE!!!! i knoe exactly what ur talking about. Mine does it to but only when i first start it up if i barely rev it, it like cuts out and the carb makes a noise kinda wierd to explain. Like the slide is poping back but thats not it. It sounds like when u "Click" ur tounge off of the roof of ur mouth but not as loud. But once it warms up it stops but it doesnt hender performance so im okay but i thought id just tell u.

pretty much what he said, it'd go away after it warmed up.

[Greg Z]

Same thing with mine but rarely does it It only does it when i first start it up and stalls out because its cold


other then that nope..

[F-16Guy]

Originally posted by EXDUNER127
I went from a 168 to a 172...
A 172 main in a stock engine???!!! My 416 doesn't run worth a crap on anything over a 165! That's WAY rich, you should be down in the mid 150's, even with the full pipe and choke removed. Drop your main down, put your needle clip on the 3rd or 4th groove from the top, and install a 40 pilot with the fuel screw about 2 1/2 turns out. If it doesn't run good like that, start looking for an air leak.

[EXDUNER127]

Yah guys, found out that my carb needed an adjustment and went into the shop today, a friend owns the shop and says he would do it for free and knock it out in a day so i can go to the dunes, next week. It seems that something was messed up with the idle, and the butterfly valve wasnt closing right-letting more air in when not needed or something like that and he said that the back fire through my carb should be cause of my carb and it is making my bike run way lean, no matter how i rejet. Lets hope this solves the problem.

[cals400ex]

Originally posted by EXDUNER127
Is that the only thing it could be?
That jet size isnt big for where i live, the elevation is 4000ft....
Will the new pilot jet help the bike start better? How bad is a messed up intake valve?


the higher the elevation, the smaller the jets you use.

[jtej]

I've had mine backfire through the carb before. I heard a pop and then it wasnt' running right. come to find out i had bent a valve and it actually blew my filter off the boot and my carb off the boot also. It was really weird. But your problem sounds like jetting as everyone else is saying.

[F-16Guy]

Originally posted by EXDUNER127
Yah guys, found out that my carb needed an adjustment and went into the shop today, a friend owns the shop and says he would do it for free and knock it out in a day so i can go to the dunes, next week. It seems that something was messed up with the idle, and the butterfly valve wasnt closing right-letting more air in when not needed or something like that and he said that the back fire through my carb should be cause of my carb and it is making my bike run way lean, no matter how i rejet. Lets hope this solves the problem.
Have him throw in a 40 or 42 pilot anyway, you won't regret it.