problems w/ '01 yz426f :(

5 replies to this topic
  • jordanf1313

Posted March 29, 2010 - 06:47 AM


so a while back i was pulling away from a stop and my bike threw a valve. head broke off into the chamber and made a mess. replaced the valve and repaired the slight damage to the piston (header was hardly even marked) and threw it all back together.

now, ive been haveing a mess of trouble getting the bike to run decent. the acceleration is garbage, top speed is half, full throttle it sputters, weak power from a stand still.

ive been playing around with the carb, origionaly the jet was set to 5 and it runs better when i put it on 3. spark plug was showing signs of a rich mix. finally got the pilot set so that the lower rpm responce is better, but i still dont have the power and acceleration that i had before.

is this a carburator problem? or do i need to tear the engine back apart and have another look at all the workings on the top end?

when i rebuilt it, i used the yamaha factory manual, to the "T". i dont doubt my work, and im certain the clearances are to the book. im just stumped now, kinda tired of tearing the carb apart 3 times a day on a hot engine

  • grayracer513

Posted March 29, 2010 - 09:55 AM


If you've had the carb apart, double check that the vacuum plate on the engine side of the slide is not upside down. The round side goes up, square side down.

  • jordanf1313

Posted March 30, 2010 - 01:32 PM


i havent completely disassembled the carb, just enough to access the jet needle. i have yet to check all of the vacuum hoses, but im sure they are clear.

ive fallowed the book pretty much word for word and from closed to 1/4 throttle it runs smooth and just fine. the pick up and power stops there though. probably from about 1/2 to full throttle the bike just makes more noise, no acceleration.

could it be a clutch issue? the bike has a Rekluse z-start with the perch adjuster that i had to disconnect to access the header. ive since left it disconnected.

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  • grayracer513

Posted March 30, 2010 - 02:15 PM


Clean your air filter lately?

  • jordanf1313

Posted March 31, 2010 - 12:25 PM


when i had it all appart i cleaned out the filter. ill try running it without the filter, just remove it all together. it doesnt sound like it has breathing problems, but then again i also have a DR.D exaust on it, lol

  • jordanf1313

Posted April 06, 2010 - 08:47 AM


ok, new development maybe. i think the z-start is screwing everything up. i dont recall the possition of the cables before i disconnected all ot it, and since then i have played around with different possitions with different results. i have the perch, but what i really need is a picture frome someone who has a good working bike with the z-start installed and a pic of the right side where the cluch cable connects to the trans.

anyone out there have a 426 with a z-start???

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