01 YZ426 valve check question.

5 replies to this topic
  • shimla4

Posted April 21, 2009 - 05:30 AM


I just went thru a long process of doing mods to my bike:
1) New 03 450 exhust cam.
2) New cam chain.
3) Check the valves.
After installing the cam and got the timming correct I only rode the bike for about 10min slowly to make sure every thing was turning over smooth and nothing was bound up. It started after 5 kicks.(Saterday)

Tuesday I wanted to start it and ride for a bit. Doesn't want to start. I pulled the plug and it was black.
So I followed you all's advice and-
4) Carb taken off and cleaned
Stock Jetting- Main Jet: 162
Pilot Jet: 42
Starter Jet: 72
5) Exhaust repacked(It was all burned out).
6) New plug

Yesterday kicked for about an hr with no luck(started once ran 5sec popped and died)
7) Pulled the tank of and check the valves and this is what i got, working from left to right on the bike(flywheel to kickstarter side)

Exhaust Left 0.229mm Right 0.254mm
Intake Left 0.152mm Centre 0.152 Right 0.178mm.

Will these clearances cause the bike not to start?

Thank you for any help.

  • grayracer513

Posted April 21, 2009 - 06:48 AM


Exhaust Left 0.229mm Right 0.254mm
Intake Left 0.152mm Centre 0.152 Right 0.178mm.

Will these clearances cause the bike not to start?

Typical frickin' 8 year-old YZF. Every one of them is within spec. Why would they cause it not to start?

  • shimla4

Posted April 21, 2009 - 07:10 AM


I am trying to make the bike easier to start and have accomplished the opposite so far. You have stated in some of your other posts that out of spec valves can cause hard starting. I don't know where to go from here other than the shop which is a rip off but I don't know anymore.:banghead:

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  • grayracer513

Posted April 21, 2009 - 01:31 PM


Pretend you never saw the bike before. What would you check?

Check the cam timing again.
Check to see if the TDC mark on the flywheel is actually at TDC by probing through the plug hole to feel the piston with a screwdriver, etc.

  • aj_yz426

Posted April 21, 2009 - 01:45 PM


Exhaust Left 0.229mm Right 0.254mm
Intake Left 0.152mm Centre 0.152 Right 0.178mm.

Those are pretty close to spec: ex 0.20-0.25mm and in 0.10-0.15mm
Shouldn't cause the starting problem.

I would make 100% sure the timing is correct, confirm TDC with the screwdriver in sparkplug hole trick, take pics and upload if you need somebody to take a second look at the timing. You probably know the stock 2003 ex cam punch marks will not line up as in the manual on the 2001 so you will have to count links.

  • jimmydoorlocks

Posted April 21, 2009 - 02:38 PM


I had some of the same problems with my 426 that I just finished and got running.
The difference for me between unsuccessful kicking :banghead: and a running bike :banghead: was triple checking EVERYTHING that I had done (timing, TDC, vavles, torque specs, etc.), a real good carb cleaning, a fresh plug, and fresh gas. After that, it started on the second kick.
Good luck!! I hope you get it figured out. :banghead:

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