06' YZ450F cutting out!

4 replies to this topic
  • gotsand_450

Posted June 03, 2008 - 05:08 PM


My 450f just started cutting out real bad. Kicks over 1st or 2nd kick everytime! Idles good...but when I accelerate through mid-range and top range it starts to cut out bad. It happens through all gears. I just had the top end redone: ground valves, new seals, etc. I haven't rejetted the carb in a while so I did that. I just changed the main jet from 170 to 168. Maybe a bad thing? I know standard is 165 but my bike is piped so I heard your supposed to go up. And my pilot screw is a 45. maybe needs to be bigger? I ride a lot at the dunes (lower altitude). Maybe its not even the carb? I don't know. Any help would be appreciated. I've ridden 2 strokes my whole life. I'll admit it...I'm a newbie to the 4 stroke world

  • RocketScientist

Posted June 04, 2008 - 03:43 PM


If this happened right after the top end was rebuilt, I would take off the valve cover and double check the valve train. Double check valve clearance and cam timing. If you are 100% it is correct, then it is most likely the carb. If you have ever taken the needle out of the carb, you may want to check it for damage. They are pretty easy to bend and scratch.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • gotsand_450

Posted June 04, 2008 - 04:04 PM


Already checked valve clearance. Tearing the carb out tonite to rejet the whole thing. Needle, main, pilot, everything. Hopefully thats the prob.Thanks for the input!

  • schmity1234

Posted June 04, 2008 - 04:07 PM


play with the fuel screw a bit. You might be running it lean after you put in those new jets.

  • RocketScientist

Posted June 05, 2008 - 11:54 AM


Valve clearance ok, but did you check the valve timing?

Related Content


Chubby dad, looking at bikes , First trip to the orange/black forum ! by Slow_ride

Dirt Bike   Make / Model Specific   KTM   250-530 EXC/MXC/SXC/XC-W/XCR-W (4-Strokes)
  • Hot  28 replies
WR Camshaft Swap Info - last post by jamesm113

WR Camshaft Swap Info

  • 0 replies

05 yz450f not fast enough by RedeyeYZ

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  38 replies

Snake pit oct 30th by The Anvil

Dirt Bike   Dirt Bike Regional Discussion   California
  • Hot  293 replies

James Stewart back on a YZ450F by YamaLink

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  47 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.