Jetting for FMF Q series muffler for YZ250F

[602R]

I have an 03 YZ250F. I put an FMF Q series spark arrestor/muffler on it. Bike had excellent power before throughout the entire power band. After muffler installation it had a dramtically decreased bottom and no top end. Total let down. On mechanic's recommendation I increased the pilot from a 40 to a 42 and the main from a 178 to a 180. Improved the mid and top but still blubbers on the bottom, from 0-1/8 throttle. Any recommendations? The clip is in the center- 4th position I think.

 

[gcoleman]

I just recently installed the QP Silencer from Purely Custom on my 04 Honda CRF 450R, and I love it! I've had no loss of power, and the cost was a fraction of what the FMF Q muffler would have been. I researched closely all of my options, and checked the Dyno Testing at Purely Custom. Sure enough my power to dB ratios were right on target. It feels like I've even gained a bit of power.

I know you're already into the FMF Q, but it may be worthwhile to check into the QP Silencer if you’re not able to resolve your bottom end drag.

Greg C.

 

[MarkSims]

My thoughts are that the Q wouldn't flow as well as the stock silencer, so you would have to jet leaner. Someone on here must have jetted from a race pipe to the Q - as opposed to going from a trail pipe like on the XR400 to a Q.

Feel free to disregard what I'm saying - since I have no experience with the Q. I'm just making a general observation.

 

[Radbuster_1]

I did the same to my YZ450 '03 and also a PowerNow. The needle clip seems ok, but I had to go one leaner on the pilot and one leaner on the main. On the contrary, my bike has so much pull it has only become easier to ride.

On my earlier WR250F '01 I changed fron the stock boat anchor to a loud WB E-series, went richer, an whoa! what an improvement. It seems the back-pressure effects the 250F's a lot.

Good luck with you jetting since it's really important.