Jetting help FCR39MM/HMF exhaust

[pnut420]

I was running a Sparks X-6 on my brothers stock 400ex with a FCR39MM with a a 165/52 and it ran great, cut out a little on the low end but thats it.

Well I took that pipe off cause its mine and put a full HMF on there with the same jetting and it was running rich and would backfire here and there. So I changed the pilot to a 50, and turned the fuel screw in a 1/4 turn more and it is still running rich and it actually backfired a flame out the exhaust, Ive heard of this happening but didnt know it would be that bad. I know that jetting has to be fairly close, but I cant get it to run good down low off the pilot or mid or top.

What should I do try running a 158 main with a 48 pilot, and what position should I put the clip in???

Your going the wrong way jet richer. go a jet up on the main and put everything back the way it was.

the pilot is for idleto 1/4 only i think you should put back the jets you had with just the slip on. and go 2 jets up on the main.Once you go up on the main try playing with needle height, perhaps dropping it 2 clips?(all these recomendations is with the jetting you had

did hmf reccomend a different needle?

it sounds like you lost bottom end fom the free flowing pipe.

[pnut420]

Originally posted by BeeeRock!
Your going the wrong way jet richer. go a jet up on the main and put everything back the way it was.

the pilot is for idleto 1/4 only i think you should put back the jets you had with just the slip on. and go 2 jets up on the main.Once you go up on the main try playing with needle height, perhaps dropping it 2 clips?(all these recomendations is with the jetting you had

did hmf reccomend a different needle?

it sounds like you lost bottom end fom the free flowing pipe.

I had a sparks X-6 on it before and it seemed to flow better than the HMF. The HMF is full exhaust as well. As soon as I switched to the HMF it started to run terrible. It seems like it is flooding out and the exhaust smells like their is alot of unburnt fuel is why I was thinking I was running rich. If I slowly push the throttle it will run pretty steady but as soon as I blip the throttle at all it wants to cut out. The only thing I changed since I put the HMF on was go from a 52 to a 50 the pilot. Im going to try to get ti dialed in but if I cant the HMF goes in the for sael section and I will put the Sparks back on. (Not saying the HMF is bad, I just can get the Sparks jetted good:mad: )