FMF Powercore 4 Exhaust


Not sure if the jetting is correct on machine. I jetted the quad as directed by FMF:

40 Pilot

152 Main

Remove Snorkel

Seems to be a dog when hitting the throttle and even sounds fat. Pulled the plug and it was black. Any suggestions?

All these jetting recommendations do, is get you in the ballpark. They also can't fully take into account the other mods you may or may not have made.

Jetting is more art than science! You can't jet "by the numbers" and you sure can't jet over the internet. You need to start out a little rich, then back it down until it just begins to run a little lean, then back it back up a bit to be sure you will never be lean.

If you aren't up to it, have it done by an experienced professional!

I have done been tuning carbs on my sleds for awhile now. I understand how it works. Yes I know it takes time to get it just right, I guess I should put some more info in the first message. I live in Northern Indiana and ride up in Michigan as well. I was hoping that someone would have a better idea to get me closer than I am with the jetting. I can not imagine I am the only 400EX owner that has had this problem. Anyways 500-800 above sea level and temps between 40 and 90.

Not sure if the jetting is correct on machine. I jetted the quad as directed by FMF:

40 Pilot

152 Main

Remove Snorkel

Seems to be a dog when hitting the throttle and even sounds fat. Pulled the plug and it was black. Any suggestions?

It sounds like you might have a stuck choke or maybe you just need to remove the airbox lid, and see if that makes any difference.

My son is running a 42 pilot and a 160 main at 4500-6000ft with no problems whatsoever!

.....And yes you can jet over the internet!....:bonk:......

The jetting sounds close. You shouln't be having these problems with it.

When you removed the snorkel did you also remove the airbox lid? If not, do so. Also, is your air filter good and clean? A dirty filter will make your machine seem to run rich. Have you adjusted your fuel screw? How many turns?

i have the same setup as you do and i used the dynojet kit i followed the stage 2 directions and the quad rocks....

i started just with changeing jets but the dynojet kit changes the needle also mod ever for the money

This thread was started 3 months ago. What is the current set up? I wish these threads had closure. People come on here and post but never reply.

People come on here and post but never reply.

Yeah....I get irritated with that. But, I do forget too follow up occasionally..:bonk:

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