ok i had put a fmf factory 4 slip on, onto my yfz and i used a 162 MJ cuz thats wut fmf called for and backed the air/fuel screw out 2 3/4 turns but yet my plug is still black and when u nail on it from low RPM's it like cuts out, and it it spits flames and pops on deacceleration, and now when i turn it off it backfires, but i think thats cuz i havent adjusted the valves yet, but anyways do u think i should try jetting down a size or 2?

 

Try 180 Main Jet

 

y would i put a bigger jet in when im already running too rich?

 

Have you also removed the airbox lid?

If so, you should probably be around a 170 main jet, Stock needle on the 4th or 5th clip position, and at LEAST a 45 pilot.

Fuel screw should be AROUND 2 turns out.

Hope this helps![img]i/expressions/face-icon-small-wink.gif[/img]

 

Whats your altitude and temp. Did you increase your pilot. Did you drop down a clip on your needle. Is your airbox lid on or off. Need more info bud. If it was me, I would make sure your airbox lid is off, and start out with 45 pilot, 168 main, 3rd clip on NCVQ needle or 5th on stock needle at 1.5 turns out. That set up should get you real close for 0-1500 feet elevation for 60-75 degrees.

 

airbox is on i tried it with it off but didnt help i live in upstate ny idk the elvation, but the fmf book calls for 2 3/4 turns out and a 162 MJ and the needle at the 4th position but with these my bike runs rich the only thing i can think of it lowering the jet, cuz idk y u guys want me to put a bigger jet in it when its runnin rich wut would be the point for that?

 

Thats why you take your lid off. Give it more air and bigger jet. It will become a completely different bike. Whats the point of having aftermarket pipe if you stay at stock jetting. You are barely above stock as it is right now, the problem your having is your not letting the motor breath. Open up the intake and make full use of your new exhaust. My white bros exhaust came with a 45 pilot and a 168 main specifically to be run with the lid off. This site will help you. link

 

I have the same setup you have.

Don't use the jet kit that comes with the factory 4. Thats actually dynojet's kit and it sucks. the numbers are all different and it doesn't come with a pilot jet. Ignore what FMF's site says.

I'm using a 168MJ 45 PJ, 2 turns on the fuel mixture, no air box lid, and 3rd clip on a NCVQ needle. That works well from 0-3000 ft elevation.


Even if you use the largest jet that comes with the FMF power up kit, you are still WAY to lean. Do yourself a favor and either go buy the Gyt-R jet kit, or go buy the jets individually.

 

Deimos;
That is a very good site!
I learned a quite a bit from those guys! Its nice to have someone to do all the foot work for you!
Dogriders are awesome!
I'd sure like to meet them some day.[img]i/expressions/face-icon-small-wink.gif[/img]

 

Ditto *****...I agree with Gummy. That dynojet kit is a bad deal. It will really screw you up. I made the mistake of buying one my first time jetting. Never did get em to work. The GYT-R kit is about $50 and will have everything you need including the NCVQ needle. You might save $10 buying indivdually, but it always seems like the shops dont stock the needle.