Just received an answer from FMF Racing about jetting for the slip-on FMF on my Raptor. According to Mike Fairbanks of FMF Racing, they are running 145/150 instead of the 140/145 stock jets. He did not mention pilot jets.

 

Raptorrider2001, Just wondering if you installed just a pipe or complete syst? I just installed the power Core-4 sq pipe alone and am having problems. How did you getin touch w/ Mike @ FMF? e-mail or phone? I e-mailed him on 1/6 and have yet to hear from him. Please advise me if the jetting change worked.

 

I did not install the whole system. Just the muffler. I emailed FMF back in early Dec. and only recently received an answer. I thought it was interesting that I talked to a Raptor owner several weeks ago and he had just put his on that day and said he called FMF and was told he did not have to rejet. I have not had any problems as yet so I have not rejetted. I just copied the phone number of Sudco and will order a couple when I get around to it. I have not taken a plug reading yet but have purchased some new plugs so I can do so. It is just one of those "round-to-its"

 

Raptorrider2001, What elevation are you riding at? I am at aprrox 650' above sea level, located 50 miles from Chicago, IL. in NW Indiana. The problems I am having, are 2. 1) When running at half throttle then hitting hard to full my bike pops and hesitates then takes off. 2) When jamming through a couple of gears then pulling in the clutch reving back to idle, if I give it any gas at all it stalls. It will start up easily, but I was not having these problems prior to installing this darn muffler. I also, was told no re-jetting would be required, prior to buying this. I don't have a problem with re-jetting, it would just be nice to know what to expect.
It sounds like you aren't having any problems? You haven't re-jetted? Well, I hope you have had better luck than myself. Let me know.

 

The elevation is about the same as yours. 600-700 ft. I have to knock on wood because I have not had any type of coughing or sputtering problems. Run yours at the speed you are having trouble and shut off the ignition at that speed. Pull the plug and see what it looks like. It should have a tan or brownish color. The whiter it looks, the leaner it is running up to the point it will blister the plug and/or damage a valve of piston. The plug number for NGK is DPR8EA-9 and the part number at most auto part houses is NGK 4929. I think they cost me about $1.25 here in the Dallas area. Probably a lot more at a Yamaha dealer.

 

I'm running the 145/150 combo at 3500' with a white bros. R4 slip-on on both of my machines.
Let me tell you it will wake the sleeping beast.

Run at 600' you should be closer to 150/155 area.

Happy Trails

 

swytak
I'm assuming its alot colder where you are then
dallas where Raptorrider2001 is which will make it run leaner, im running a little lean with the stock pipe here in maine where the temps are 20-30 deg. I'm waiting on jets and am going to try the 145/150 combination would think with the pipe and cold air you may need even more jet

01 Raptor/blue
87 Quadracer 500

 

2strokeDiehard,
What elevation are you at? If I go with more than 145 - 150 now that it is cold, will I need to rejet when it is 90 degrees? You are right, it is only 20 - 30 degrees. I have been looking at dynojet. They are saying to cut the flaps out of the snorkle, with the after market pipe, using dynojet jets run 144-146 mains, no change of pilots. This is the recommendation for under 3000'. Reply when you get a chance. Also, let me know how your jetting change worked. Thanks!

 

I'm at sea level and rarely ride any more then maybe 600-800 feet above sea level, I
checked the plug in october a couple of times when it was about 50-60 deg. and it looked to still be a little lean with the stock jets, i wouldn't think 145 150 main jets would be too much in the summer at sea leave with an after market pipe,I haven't tried cutting out the flaps yet but am going to try it as soon as i get the jets changed! how does that pipe sound?? I wanted to get it but don't want it to be too loud

 

2strokeDiehard,
I have the FMF Power-Core 4 sq slip on. It has definately improved the power through-out. My Raptor is not running all that bad, I just think it could be running better. The FMF is not that loud, it is throatier. I have heard several other pipes on Raptors and the Power-Core is in the middle. Do to me riding on the farm (woods and open fields) I do have neighbors who would not appreciate a full race exhaust. I just spoke with a guy at dynojet. He is confident I can run a 144 and 146, cutting the flaps out of the snorkle and the slip-on. Check out dynojet if you get a chance, I just ordered mine. I'll let you know how they work next week.