what the *%%#$!

I ride at an average ele of 6000ft. I too experienced a huge loss of pwr when I put the pwr core on. (pwr core 4 squared). I thought of throwing it away but i need a spark arrestor.

Bottom line - my settingd that finally worked. BK mod apporx. 1mm or roughly .5sec, 158mj up from 155 after the BK Mod, stock pilot, needle one clip lean or up one from stock, and fuel screw between 1.25 and 1.75.

It finally works, be patient!


Try a 40 pilot.

my 01 426 has no power on the bottom. i just put the fmf power 4 Q exhaust on and couldnt even make it up a hill in 1st gear that normally 2nd and 3rd rip up it. mid range to top end is great though. i even went back to check the settings of the bk mod, timing and duration of the squirt were right on. my settings at 8000' are 52 mj, #4 needle position, up from #3 after installing pipe, 1.5 on fuel screw, 42 pilot jet. i played heaps with the fuel screw to no avail, and the mj seems fine, and i dont think the needle could effect it this much. please help!

Did this start immediately with the addition of the new muffler?

If not, then check your valves. Overly tight valves on a 4-stroke can hang open and the most noticable loss will be down low. If this is the case I would adjust it before further riding. A leaking valve can burn the seat and the valve.

If this started as soon as you put the new muffler on then it sounds like either you've got some tuning to do, or the new muffler isn't so good for bottom end.

yes this started with the new pipe. does anyone know if this pipe is restictive in air flow? i called fmf and the tech person said it was restictive but then went on to say the fmf settings at sea level were a 168mj and 2.75 turns on the fuel screw. when asked about his contadictory statement he then said the pipe was not restictive. so now im not sure.

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