back firin

4 replies to this topic
  • mat

Posted June 20, 2001 - 05:39 PM


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

  • Guest_Guest_*

Posted June 20, 2001 - 06:13 PM


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.

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  • Roostn67

Posted June 20, 2001 - 06:39 PM


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

  • Boit

Posted June 20, 2001 - 07:38 PM


My '00 once was backfiring horribly....and running bad on the top-end. I assumed it was my jetting. It wasn' was an air leak where the airbox mounted to the carb. A leak where your header mounts to the head can cause this 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 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.

  • mat

Posted June 20, 2001 - 07:54 PM


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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