426 No Compression....

1 reply to this topic
  • johnnyuterus

Posted October 08, 2009 - 06:50 AM


Bike was running A1 aside from an impeller shaft. I tore off the clutch plate cover and right side casing to replace the impeller shaft, a new seal, gasket and bearing and put it all back together..

First thing I noticed was no compression, I could kick right through it like a 2-stroke. I used to be able to stand on it.

It is quite cold out now and it hasn't been started in a few weeks, so I primed it with a few squirts of gas and it came to life with the cold choke on. After a while I pulled the choke in and it came to a nice idle but after a few mins it just stalls. I was unable to get it started again unless I primed it with gas first and had cold choke out...and same thing, everytime I manage to get it started as a few secs after it comes down to idle it dies....and still no compression in the kick.

I noticed after everything was reassembled a small piece lying on the ground, it was some sort of guide or something that was in the side casing

here's a pic------>

Posted Image

Any idea's ???? this is my first time working on a bike and I could very well have mucked something very simple up...

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

Posted October 08, 2009 - 09:02 AM


That sleeve and O-ring are number 12 & 13 in the picture here. It's function is to seal coolant out of the engine oil (nothing important) as the coolant passes from the water pump to the crankcase, and then to the cylinder.

Your starting problem is apt to be a clogged pilot jet, or bad gas, although the lack of compression when cold could be a valve clearance issue.

Related Content


Thinking about Yamaha 250... by Arctic Pride

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  491 replies

Snake pit oct 30th by The Anvil

Dirt Bike   Dirt Bike Regional Discussion   California
  • Hot  293 replies

First Hare scramble tips by dhend8

Dirt Bike   General Dirt Bike Forums   General Dirt Bike Discussion
  • Hot  33 replies

Michigan Motocross Tires by 288yz450

Dirt Bike   Dirt Bike Regional Discussion   North
  • 1 reply

yz250x vs 450 4t comparisons (preferably desert riding) needed by JakeNorthrupYZ450F

Dirt Bike   Make / Model Specific   Yamaha   Yamaha 2-Stroke
  • 9 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.