2001 yz426 jetting issues

hey guys i need some info about the new FMF Q-series muffler, i usually ride in elevation of 2000-6000ft, what jets and accelerator pump setting settings i need. And the air screw.

I had that pipe on my ’01, with stock header, for about three months. I don’t know that the addition of that silencer in and of itself makes enough of a difference to warrant a jetting change, but it might. In my case I put the Q on my ’01 when new then jetted the bike, but I didn’t notice much of a change when I put the stock exhaust back on.

At any rate I ride at 4 to 5 thousand feet and spent a fair amount of time dialing my jetting so hopefully it will work for you as well:

160 Main

40 Pilot

Adjustable PAJ (avail from Sudco) to replace 100 PAJ, I have it set at ~ 85

Stock needle (EJP) at # 3

Idle Mix 1.5 turns out

BK accelerator pump stroke set at 1 mm at the rod (and to hell with the stopwatch method)

¼ turn additional pump delay over stock

And I am running with the Main Air Jet removed.

As for your silencer keep an eye on the four mounting screws that secure the can to the collector. They will tend to work loose over time because the bulk of the can’s weight is aft of the sub frame mount, and the thing tends to vibrate and move about this axis since the mount isn’t affixed to the can (it just wraps around it).

I kept an eye on these screws but ended up losing the thing in a race anyway. I did drop the bike on that side too, I’ll admit, but IMO FMF should have put springs on the silencer to collector connection, ala Yosh, to prevent the thing from wiggling loose.

Hope this helps.

BTW you can call Sudco at 800-998-3529. If you are up for it the adjustable PAJ is very useful, especially if you find yourself running a 40 pilot. Fine tuning this circuit allows you to find easy starting and best idling mannerisms with the fuel screw while curing the popping and surging and low to closed throttle with the (pilot) air screw.

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