YZ450F hard starting, won't stay running

3 replies to this topic
  • Larrykay5

Posted June 25, 2014 - 06:05 AM


Cleaned carb, fresh gas, clean air filiter, gas flowing thru carb OK. Starts with starter fluid, starts when I crank throttle 3-4 times, runs 5-10 seconds then quits.  Valves check out except one exh vlv at .016" spec says max .010".  Seems like a fuel problem?? ...or is it the exh vlv clearance? Thanks

  • Thommo_400f

Posted June 25, 2014 - 06:00 PM


When you cleaned carb did you remove and clean pilot jet?

Is the throttle slide valve in the right way up?

Is the carb sealed all way around with no air leaks in the boot?


I'm thinking most likely blocked Pilot...

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  • dirtbeater

Posted June 25, 2014 - 07:09 PM


Some times a clogged pilot will run very poor at wot but will not idle.

  • leo 450yfz

Posted June 25, 2014 - 10:59 PM


Not sure if it's the same carb, but on my 2005 yfz450 (fcr flat top 39mm). If you cleaned the inside of the carb with carb cleaner, and really sprayed it you could have damaged the o ring on the slide. Also the slide has coating on it, that heavy duty carb cleaner can take off. If you actually took the slide out, make sure you didn't put it in upside down. Basically you want to use the carb cleaner on the bowl, but not on the slide.  And the last thing, I would say make sure the pilot jet is not clogged, but since it ran fine before, I doubt that it is.

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