YZ400F hard to start when lukewarm


4 replies to this topic
  • rdefonce

Posted September 06, 2008 - 03:21 PM

#1

My 400F normally starts fine when cold, and starts fine when hot (using hotstart)
BUT

when it's lukewarm (starting between rides, maybe 30-45 minutes downtime) it does NOT want to start.:-o

Any clues why not??

  • rdefonce

Posted September 06, 2008 - 03:23 PM

#2

Oh, forgot to mention that I have tried (when lukewarm) starting according to manual. (no priming, no choke) and tried with no priming, WITH choke, AND tried with priming and choke! No luck.

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  • Petrasunas

Posted September 07, 2008 - 07:40 AM

#3

I have a 98 yz400f and I have found that when I don't allow it to warm up. and stall it. Its a son of a gun to start. My bike starts first kick hot with hot start and a lil crack of throttle or cold with choke no throttle.

  • brucifer

Posted September 07, 2008 - 05:57 PM

#4

I just noticed the same problem. I have been riding my piece built yz400 with a 03 250f carb,(the one with the hotstart out the top). I switched to a 01 426 carb and in trying to adjust the jets on the stand didn't let it warm up enough, and killed it. It kicks like it hydraulic locks, Hurts my foot. When it is up to temp with the 250f carb it starts first kick all the time. Try again tomarrow.

  • rdefonce

Posted September 08, 2008 - 07:53 AM

#5

I have a 98 yz400f and I have found that when I don't allow it to warm up. and stall it. Its a son of a gun to start. My bike starts first kick hot with hot start and a lil crack of throttle or cold with choke no throttle.


Yeah, sometimes my bike exhibits that too, if it stalls after first starting it.

Mine is slightly worse than that though; used to always start, but over the years has grown more hesitant. Thought it could be valves needing adjustment, just did that, were not very far out, but now they're perfectly in spec. STILL same symptoms.
Perhaps I should remove the carb to check for dirt in starter jet and/or pilot jet.

Lastly, could it possibly have something to do with the fuel screw? It's adjusted to 2 turns out.





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