air going in exhaust coming out carb

1 reply to this topic
  • monicakas

Posted June 07, 2008 - 10:08 PM


I have a 2005 YFZ 450 that wont start, when turning over air is being sucked into the exhaust. Ive checked the timing and the cams. does anyone know what would cause this?

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • grayracer513

Posted June 08, 2008 - 06:55 AM


To some extent, this is normal. The exhaust valves don't close until about 30-40 degrees after TDC on the intake stroke, and since the throttle is closed, the engine will, at cranking speeds, draw some air through the exhaust.

The intake also remains open into the beginning of the compression stroke, so some air coming out of the carb is normal too.

If any of this is happening in excess, your cam timing is off, or you have bent or leaking valves. Re-check the timing, and not whether the engine has the normal amount of compression.

Related Content


Michigan Motocross Tires by 288yz450

Dirt Bike   Dirt Bike Regional Discussion   North
  • 1 reply
WR Camshaft Swap Info - last post by jamesm113

WR Camshaft Swap Info

  • 0 replies

YZ450F 03 Sparks driving me crazy by SirAttard

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

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

Snake pit oct 30th by The Anvil

Dirt Bike   Dirt Bike Regional Discussion   California
  • Hot  293 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.