back firin

i recently noticed my 99400 backfires when i chop the throttle, it has a white bros pipe(full system) and air filter, i know its jetted correctly and just cleaned the discs and filter, does any one know if this is normal or not

Matt, its not normal. You either have a leak in your exhaust system (it will suck air in on decel) or your fuel screw or pilot jet is too lean. Keep in mind that correct jetting on a warm day will be lean on a cold day.

My bike (2000) backfires a lot. I have an FMF Powercore 4^sq with a 152 main and stock fuel setting, stock pilot setting. I'm in Denver at 5,000-13,000 feet. I never change my jetting, I just leave it alone. I know from watching the list that I have the leanest setup around. Does anyone else even come close to my settings? Remember, if you don't have the same pipe the numbers won't work out.

I would like to know what to set my main at if I go to Arizona. I plan on riding the Snowflake 100 in Sept. I have no idea what to jet it at.

Roostn in Golden

My '00 once was backfiring horribly....and running bad on the top-end. I assumed it was my jetting. It wasn't...it was an air leak where the airbox mounted to the carb. A leak where your header mounts to the head can cause this as well...as was mentioned. Once my leak was corrected, I put my efforts toward jetting precision. The nice thing about the 426 is that main jet can be changed in less than 5 minutes. Lots of guys loosen the clamps and spin the carb to get at the jet while that's just not necessary...plus it adds to the risk of causing a new leak. Simply turn off the petcock and drain the float bowl. Remove the plug at the bottom of the float bowl with a 17mm boxed in wrench(offset works great). The main jet is offset toward the rear of the carb(toward the rear wheel). Take a 1/4" drive 8mm socket and slip onto the jet with your fingers, then slip the ratchet on and remove the jet. Installing a jet is a little trickier. Drop the jet into the socket and start it with your fingers taking care to not cross-thread it. Snug it on down before putting on the ratchet and then snug it down a little more. These are brass so you can't put much pressure on them. Put the plug back in, close the drain screw, and turn on the petcock. You're done.

thanks for the help guys, come to think of it i did notice a leak recently where my white bros header meats up with the E-series pipe, anyone know what seals that up good or should i just replace the little asbestas doughnut thingy in between

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