Bah backfiring.

[Mx_523]

I have a Curtis Sparks x4 exhaust on my 300ex. Right now it backfires. I have a 135 main jet and I believe a 38 pilot jet. The screw is turned 2-1/4 turns out, and the clip is in stock postion on the needle. It accelrates and idles perfectly. When you give it gas to anywhere more then 1/4 throttle and let off of the gas it backfires. Would a 42 size pilot jet solve this problem? It also has a K and N air filter with an outwear and no air box lid.
Thanks

[LT250RMan]

have you checked your spark plug? What color is it?

[GPracer2500]

Originally posted by Mx_523
[snip]....Would a 42 size pilot jet solve this problem? It also has a K and N air filter with an outwear and no air box lid.
Thanks

Most likely. A 40 might do it also.

[06_yfz450_king]

Is there any really small holes in the exhaust system, if there is it will backfire.

[06_yfz450_king]

O-and also the header ma be loose.

[Mx_523]

Originally posted by LT250RMan
have you checked your spark plug? What color is it?
I have not check the plug yet, but I will today.


Originally posted by 06_yfz450_king
Is there any really small holes in the exhaust system, if there is it will backfire.
There aren't any holes in the header part. But when it goes up to the canister part, there are holes where the old rivits were drilled out. You know what I mean? Would that cause it to backfire?


Originally posted by 06_yfz450_king
O-and also the header ma be loose.
The header is tight.

Thanks

[big_saxy]

135 seems really rich on your pilot. I have the exact same setup as you except for an hmf pipe and i have 128 main, 40 pilot, need clip one down from stock and if i remember right, 2 or 2 1/2 turns out. You can play with that one a little. But i used to have the same problem as you, back fired like crazy whenever I closed the throttle. After i put the 40 pilot in, it fixed it right up. I have nice quiet and smooth deceleration now. Also really really helps the quad start when the temp is below 30 degrees. Hope this helps!

[Mx_523]

Well I just tried a 135 main jet and a38 pilot jet and its to lean. I'm going to buy a 40, 42 pilot jet 128, 132 main jet and see what happens from there.

[06_yfz450_king]

mx_523: There aren't any holes in the header part. But when it goes up to the canister part, there are holes where the old rivits were drilled out. You know what I mean? Would that cause it to backfire?...

I dont think it would because its at the end of the exhaust.