Backfire and Hesatation

I have 01 YZ426F with aftermarket exhaust installed and jetted by the dealer. once i got it home i took test ride and got a little hesatation between 2nd and 3rd, also alot of loud backfires on deceleration. I am wondering if the bike is jetted wrong, or if cold rainy weather could cause this..... The only jetting change the dealer made was changing the main jet to a 160 from a 162 and said i was good???? PLEASE HELP


I had this same problem when I put my E-Series exhaust on.

You need to turn your fuel screw out 1/4 turn at a time until the backfire stops or at least becomes less noticable. My 400 still backfires slightly but it runs so good with no hesitation I don't want to mess with it. If you get much past 2 1/2 turns (from fully closed) then you will need to go to the next size pilot jet. My 400 came stock with a 45 I now run a 48 with about 1 1/2 turns out on the fuel screw. You will need to check and see what the stock jetting is on the 426 since it is different from the 400. It runs real crisp and clean. I haven't run it with this rain we are having but I suspect I would have to turn it out 1/4 - 1/2 turn if I did. With weather like we are having here it makes for a lean condition since the air is more dense.



99'YZ-400 (Mine)

00' TT-R 125 (Hers)

91' KX-125 (Son #1)

93' CR-80 (Just sold it. Looking for another TTR125 for Son #2)

99' PW-80 (Son #3)

If it's backfiring that means it is running lean. I have an '01 YZ426 with an E-Series. I ride and race between 2000 - 4500 FT. This works for me:

162 Main

45 pilot

2 turns out on fuel screw

needle on 3rd clip (from the top)

[This message has been edited by FlyGi (edited 04-08-2001).]

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