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I have an 08 450x. Newer rebuild SS valves which are in spec. The issue is the beast will not start cold with the kicker EVER!! Some idiot forgot to but the battery tender on (me) and I had to try kicking it this morning. I stopped when I had a blister on my foot. The odd thing for me is... Once it is started even for 30 seconds you can kill it and it will fire immediately. It is worse if it has been sitting for a few days. However if the battery is charged, couple twists of the throttle, choke open, bump the button and BRRRRAAAP! *shrug*
I do suspect I have some AP issues as I have the flame out issue off idle occasionally. Thats not going to keep it from starting though... right?
Thoughts are appreciated!!

Have you checked to see if the squirt is missing the slide ? , that is a good indicator of AP timing , if it hits the slide it will be hard to start , the gas has to get past the slide it should just miss it and give a nice long squirt , if the squirt is short it may be the AP diaphragm might be bad

What is your (kick) starting procedure ??

I would think 4-6 twists of the throttle , choke on , get it up on the compression stroke , and give a full hard kick (no wimpy 2 stroke kick when cold) and it should fire right up within 1-3 kicks


Does it pop on decell after started ??

Have you checked the jets ?? , as in are they stock ?? , do you know the size ? , what is your altitude ??

If you have ruled out valves then it has to be a fuel issue

Hot Start sticking
Clogged or incorrect for elevation jetting
Fuel Screw in too far
AP Timing
AP Diaphragm
Incorrect Starting Procedure

Thanks Jim. I completely agree with your diagnosis. However I'm not sure where to start. Again the thing that does not sit well with me is that hot or cold if you as much as breath on the magic button the beast fires.
I have not pulled the airbox or tried filming the squirt. On those very rare occasions when I do need to kick start cold my routine is simple. Three twists of the throttle with the enrichment circuit open. Get to top of stroke and let my 220 pound frame do the rest. Trust me ... I can kick. I used to ride CR500's and could start an old XR600 with out decompression.
When I kick I will get some weak attempts at starting. Never a backfire.
I have the JD kit installed as well as the Boyseen Quick Shot3. Air box open etc etc...
I'm most likely just going to rip the carb out and inspect and clean everything. Who knows... It just drives me crazy... any other suggestions or thoughts from anyone are always appreciated.

It sounds to me that the decomp mechanism needs some fine tuning. Kicking it over is where you need it to be 100% perfect set to get an easy start. when using the electric start slightly off is no big deal.
Just my 2 cents.

Thanks Neil, def worth looking at. Especially since the head is no longer stock and was changed at the beginning of last year. Though I don't remember ever successfully starting this bike cold with the kicker.