another jetting problem HELP!!

6 replies to this topic
  • YamahaYz450F

Posted June 01, 2004 - 02:37 PM


I recentally put a pipe on my yz400f and i put a 45 pilot jet in like it said but the bike still backfires in the low rpm range and also when I rev the bike up. if there is somehting i can do to make this stop let me know. thanks

  • Fastest1

Posted June 01, 2004 - 06:04 PM


Did you use a new crush washer in the exhaust? It sounds like a leak at the exhaust where it meets the head. Have you adjusted your fuel screw out?

  • YamahaYz450F

Posted June 03, 2004 - 08:57 AM


Hey no I didn't put a new crush washer in. can I buy one at a dealer? and also by accident i turend the fuel screw but i put it back at what I was told was factory 1& 3/8 turns out. if thes wrong let me know. the bike is also running rich. if you can help me that would be great.. thanks matt

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  • Vet28

Posted June 04, 2004 - 07:50 AM


allow me...ride below 1/2 throttle, but at a constant down a road somewhere. if it's smooth and not jerky your pilot is long as there are no other problems. do the same above 1/2...and check main. I put on my Jardine system, had the same problem as you and ended up at 48 PJ and 172/175 main. now, all is well.

vet28 :thumbsup:

  • Fastest1

Posted June 04, 2004 - 03:21 PM


Yes the crush washers are available at the dealer. Always tinker with the fuel screw regardless of the "stock" setting. That is merely a baseline. Where is it running rich? and why do you think it is rich? Smell? Performance? Plug? Exhaust?

  • YamahaYz450F

Posted June 07, 2004 - 03:22 PM


When i ride below half throttle the bike is jerkey and not smooth..what should I do in this case. and i also know its running rich because of the color of the plug. i have the sock pilot in the bike still. the reason i think its running rich off the bottom is because when i rev the bike it will blow flames out the exhaust. if you know what to do to fix this let me know

  • Fastest1

Posted June 07, 2004 - 04:56 PM


It is blowing flames on the stand with no load right? I would say drop the needle 1 notch or leave the needle alone and go down 1 main size. This is only if it does the flaming while riding. If it is just on the stand forget it.

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