YZ426 hard to start when HOT

6 replies to this topic
  • shrekka

Posted July 02, 2008 - 08:49 PM


Hi there
can anyone help me here
i have done a complete topend rebuild on my 426, (2002 model). l put SS valves in (thanks to TT Parts store of course :thumbsup:, new everything including rings. new plug and new oil, checked valves 50 times (exagerated)
And a new head, (long story) no leaks from valves when they were put back together
I have the YZ450 exhaust cam and now using the Hotcams inlet cam also
Put bike together, checked clearances everything l have gone over.
Bikes starts 3rd kick when cold and runs like a purring putty tat, . But after a short run in and when its HOT l cannot start it? But has been stalling quite easily, when l turn choke off.Never ever did that b4 the rebuild
The shims are 175 all around.
Could it be because the head, valves are hot and of course the metal expands, that could b the cause of the hard starting?
Should l change all the shims say to 180 or 185s and record clearances and see how it starts then?

Any ideas are much appreciated..


  • grayracer513

Posted July 02, 2008 - 09:02 PM


If your valve clearance is correct when cold, they are not the problem.

It sounds like a carb tuning issue related to the pilot circuit. That's the cause of most hot starting problems with 426's.

  • shrekka

Posted July 02, 2008 - 09:29 PM


oh ok
thanks for help
you call it the pilot circuit, would you mind elaberating on that?
Or any links relating to it...


i tried starting the heap when cold and it wouldnt start. if putting another stator doesnt fix it, its out the door. l dont want the hassels of it
i have spent heaps to get it right and it wont start again.
i surely wouldnt be surprised if its the stator, but l wont be holding my breath over it

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  • grayracer513

Posted July 03, 2008 - 05:34 AM


oh ok
thanks for help
you call it the pilot circuit, would you mind elaberating on that?
Or any links relating to it...

Pilot circuit = idle mixture.


  • shrekka

Posted July 03, 2008 - 09:59 PM


Hey greyracer

you wouldnt believe wot the problem was..I pulled off Stator today and it was caked in grey crud paste???. l put replacement stator on and checked both with mulitmeter and all in spec.
Bike shop used rattle gun to get it off for me...
Went home and put the bike together, it it started 3rd kick and purreddddd, didnt even stall when turned choke off.
it ran nicely, just like it did b4 problems occurred..
I heated it up after riding aroun my house and driveway, turned it off and it started 1st kick..i couldnt do that b4
i have been riding it this after to break it in and it hasnt missed a beat..Starts gr8 and my face is smiling agian
thanks agin for helping out


  • grayracer513

Posted July 04, 2008 - 05:57 AM


Interesting. Sounds like the impacted metallic debris that collects on the inner surface of the flywheel. The magnets attract it, and the centrifugal force throws the oil away. The old 250-305 Honda twins used to have oil "filters" that worked that way. Sounds like it was either shorting the coils, or interfering with the inductance.

  • shrekka

Posted July 05, 2008 - 03:51 AM


yes strange l reckon, but ive heard it does happen

the bike is so sweet to start it has been gr8 to see it running again
Im planning to run bike in tommorrow for the 1st time, since all the work that has been done..:thumbsup:

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