HMF Competition Full Exhaust Muffler & Jet Kit + Uni filter Jetting

[bronson]

Hi everyone, I have bought a stock 2004 TRX 400EX. I just buy the HMF Competition Full Exhaust Muffler & Jet Kit + Uni Filter.
This HMF Factory Jet Kit Includes Individual Keihin Hex 152, 160, 165, 170, 180, 190, 200 and 42 Pilot.
Appreciate your help to make the right choice on Main Jet.

[DragonGunner]

Hi everyone, I have bought a stock 2004 TRX 400EX. I just buy the HMF Competition Full Exhaust Muffler & Jet Kit + Uni Filter.
This HMF Factory Jet Kit Includes Individual Keihin Hex 152, 160, 165, 170, 180, 190, 200 and 42 Pilot.
Appreciate your help to make the right choice on Main Jet.

Put the 42 pilot in. For the main we need to know some more....whats your elevation in your area, running with lid on or off.

[bronson]

Thanks, running with lid on and under 1000 ft, near sea level

[Stickman400]

The 160 should be fine, you may even be able to get away with the 152 since you're running with the lid. Put the 160 in and see if you can run at wide open throttle without it cutting out and sputtering. If it does then put the 152 in and you're good to go. If it runs fine then leave the 160 and have fun.

[bronson]

Hi, i live under 1000 ft. run 42 pilot, 65 main jet and lid on. I'm getting excessive backfiring on deceleration and stumble at WOT. After that I took the lid of and it run OK .
The HMF manual said to use the main jet between180-190, that's correct?
I don't wanna run whitout the lid.
Thanks for your help

[Stickman400]

Try the 152 with the lid on. Don't use their guide, it's wrong for your application, 180-190 is what guys with high compression 407-440s, cam, porting, 450 carb., etc. use. It stumbled because your were too rich and not getting enough air for the amount of fuel you were delivering, then when you took the lid off it allowed enough air in to balance it back out. So lowering the main and putting the lid back on is what you need.

[bronson]

Thanks a lot Stickman400, I did what you said, now run better on top speed but in mid-range RPM it bog and get very hot. I have 2.5 pilot

[Stickman400]

Can't really see it in the video. I would say it needs the clip moved down 1 notch on the needle, probably running lean at half throttle still.

[Dritto]

I use the same performance setup and I run:

mainjet: dynojet 146 (160 keihin) /w dynojet adapter
pilot jet: keihin 42
needle: groove #3

It has very small amount of backfire on deceleration, but nothing else.