Backfires when decelerating (sp)???

11 replies to this topic
  • shanet1975

Posted April 07, 2005 - 06:49 AM


You have all been incredibly helpful with me getting my 01 YZ426 starting much easier. It was the plug after all. Talk about a pain to change that out. Well onto issue # 2. I've noticed that it takes a little to rev down to idle after I let off the gas and when decelerating she seems to backfire. I've heard that this could be the pilot screw????No manual with bike. Can someone tell me if this sounds right and if so, how to go about resolving.....?
Thanks for your time...

  • Yak

Posted April 07, 2005 - 07:32 AM


Sounds like you are a tad lean on the fuel screw. There is a flat head screw in the bottom of the carb, recessed in a hole about in the middle of the carb. It controls fuel so "IN" or clockwise to lean, "OUT" or counter clockwise to richen. Turn yours using 1/8 turn increments till the idle returns to normal right after you close throttle, this should also rid the backfire problems on decel. Dont turn OUT more than 2.5 turns total. If you have to go more turns, its time to go up one size on the pilot jet.

NOTE: bumbling/burping on decel is not necessarily bad. You just want to avoid loud backfires

  • shanet1975

Posted April 07, 2005 - 07:35 AM


Thank you so much. I will look for that tonight when I get home. Should I go all the way in with it, then back out so I know how many turns it's been, or 2.5 turns from where it is?
Thanks again.........

  • Yak

Posted April 07, 2005 - 07:59 AM


Yes, turn all the way in and then count the turns out as you go.....

Stock setting is somewhere between ~1.5-2.0 turns out

  • shanet1975

Posted April 07, 2005 - 08:26 AM


Thank you so much....I'll give it a whirl tonight and see how she does...

  • WRookie

Posted April 07, 2005 - 11:51 AM


After you accomplish the whirl try to do a search on backfires. You will gleam a whole cornucopia of information.

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  • tnl

Posted April 07, 2005 - 12:25 PM


The spell check tab on the bottom of your message will work too :naughty:

  • yamahauler44

Posted April 07, 2005 - 02:00 PM


my yzf brumbles and pops alot but i think its normal, its done that on all 4 4-strokes ive owned.

  • shanet1975

Posted April 07, 2005 - 03:05 PM


Haven't had time to give her her a whirl and probably won't tonight. Thank you all for the input and laughs. I'll be taking my daughter out on her 90 atv this weekend so I should have some time to get her just right. Hopefully.
Thanks again....

  • palmdaleRider

Posted April 07, 2005 - 03:16 PM


This is good information. My 426 had some heavy back fires. I put a quieter Yosh silencer into the exhaust canister, and that helped quite a bit. Enough that that was as far as I wanted to go, but if it's just a screw turn? Hell, shucks, I'm always ready to screw. :naughty:

  • tnl

Posted April 07, 2005 - 05:39 PM


Do a search like the other member said. Check that all exhaust connections are tight without leaks.

  • YZ250F_Rider

Posted April 07, 2005 - 05:55 PM


The best way to adjust the fuel screw is by doing it under heavy deceleration. Ride it around on the track until its good and warmed up and then adjust it until it just starts to brumble and almost pop when you are having to really hammer the brakes and pull the speed down going into a tight corner from a long run on the track.

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