My bike fouled a plug and was running really bad even after changing the plug (sounded like a 2 smoke) so I pulled of my end cap (powercore 4) to find all of the packing had clogged up the endcap to where exhaust cant get out. And since there was no packing on the core it rattled around beating up the end of the mid pipe to where the core no longer fits right (fmf says the core should be welded to the mid pipe) so I am going to just order a titanium 4 and while im waiting for it to get here I want to just put my stock mid-pipe and muffler on so I can go to the track tues. an thurs. and then race saturday! So my question is will the stock muffler throw off my jetting because I dont want to have to change it just to ride for a week and then have to change it back? In case it matters it has the fmf jetting kit. THANKS ALOT GUYS :applause:


My dads 450 had a fit when we went from a twin air filter to a stock filter, so we had to mess with the jetting. Maybe exhaust is the same way... i donno im just a 250f guy tryin to help ya out.

im just a 250f guy tryin to help ya out.


My problem (now) is im not sure if I can damage my bike if the jetting is off? All I know is that With the stock mid pipe and muffler it sounds like it runs really good but I dont know how to tell if the jetting is correct. If its off can it hurt anything?

A moderately lean condition could hurt the valves in the long run, but it would pop and backfire on deceleration and not make good power, so you'd know... Rich would bog and be hard to start. if it seems like it runs good you probably are close enough, my 400 will run the same jetting from 5k ft to 8500. outside that window it runs worse but still rideable. They are pretty forgiving Ive found.

BlueRide :applause:

OK , thanks I figured since it seems fine it probably is..

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