Help Please---YZF426 Carb Problems

4 replies to this topic
  • Rook75

Posted April 26, 2005 - 08:00 PM


New to TT and I am in need of some help!! I have a 426 and I have the infamous bogging. Well, I put on the Boyessen pump cover and I noticed that I stil had the problem. I took apart my carb and cleaned all the passages and then i noticed that when I look in the airbox side of the carb and crank the throttle, I have no spray. I was reading here on TT about the timing screw and how there is a Mod that says to lower the spray to .5 sec. That is what I was planning to do, however once I noticed that I was not getting any spray, I became worried. The bike does run fine with the exception of the bogging However, I did order a new diaphram, but I am not sure it that is the problem. Does anyone here have any tips or suggestions, I am in great need!!! Thanks :naughty:

  • Ga426owner

Posted April 27, 2005 - 07:11 AM


426's must have regular cleanings of the accel pump. diaphram etc.... it is a open unit with just a small rubber dust sheild to keep the junk out - It gets very dirty in there over time. You should also have the Boyesen gauge to set the
squirt timing screw - that should help you. Otherwise the bike is not jetted correctly.
hope this helps :naughty:

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  • Rook75

Posted April 28, 2005 - 07:47 PM


Thanks for your help and assistance. I did fix the problem. It was the little brass tips that is press fitted into the air box side of the carb. I used a surenge and shot some solvent in the passage and let it soak and it took care of the problem. Thanks again for you help, I apprecate it.

  • fattyaf83

Posted May 04, 2005 - 03:31 AM


I have a problem with the idle advancing after moving the throttle. The throttle isn't sticking so it makes me think there is something getting stuck open and creating its own circuit

  • Yak

Posted May 04, 2005 - 06:25 AM


I have a problem with the idle advancing after moving the throttle. The throttle isn't sticking so it makes me think there is something getting stuck open and creating its own circuit

Per Marc Salvisberg's FCR tuning doc:

Engine warmed up to operating temperature, and the idle speed set, adjust the fuel screw so that when you rev the bike in neutral and release the throttle, the revs quickly drop to exactly idle speed again. If, when you release the throttle, the revs hang up a few hundred rpm above idle speed, then drop to idle, the idle mixture is probably a bit too lean. Turn the fuel screws out. Use a minimum of half turn increments until you know you've just about nailed it. You'll drive yourself up the wall trying to tune the thing in eighth or quarter turn increments if you're a mile off. In extremely lean cases the idle will hunt between the proper speed and something above it. If, when you release the throttle, the revs drop below idle speed then pick up, the idle mixture is probably a little bit too rich. Turn the fuel screws in. In extremely rich cases the engine will die after revving the bike and releasing the throttle, unless you've turned the idle speed screw way in, in which case it may act like the idle mixture is a little bit too lean. In slightly rich cases, the engine will respond well to throttle blips when cold, but will die or dip slightly below idle speed when hot.

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