I've been struggling with a starting issue since December of last year. My 2011 KX fires right up when it's cold, but as soon as it gets to operating temperature, it will NOT start. Kick after damn kick and it won't start. The valves are perfectly in spec. I am at a complete loss. Makes absolutely no sense to me. Any thoughts or similar experiences would be much appreciated.

This is a 2011. FI has been remapped. It ran perfectly fine up until December of last year and then this stupid problem started (pun not intended). I can't for the life of me figure out what could be the problem. It gets hot, no start... and valves are perfect. I took it to a dealer to have them check if there were any error codes from the FI and nothing. No error codes. Only has 29 hours.

Edited by Justin Hambleton, 08 March 2012 - 04:57 PM.

You probably have a leaking intake valve. Your symptoms are of exactly that.

I'll bet it bump starts just fine when hot....

Krannie, on 08 March 2012 - 05:50 PM, said:

Unfortunately not, but I'll double check that again tomorrow. Last time I was out riding in the desert we couldn't get it bump started either. As soon as it cooled down, it fired right up.

Justin Hambleton, on 08 March 2012 - 06:04 PM, said:

Oooooh, then it's your stator or CDI. Do you have a flywheel weight?

Krannie, on 08 March 2012 - 08:32 PM, said:

No, flywheel is stock (although I sure would like one, but there's no aftermarket one for the '11 KX yet except the pricey OEM one). I've checked stator resistance cold and hot and the ohms are in spec.

I think my problem is definitely electrical (or fuel pump). Question is where do you start? FI can be a PITA at times like these.

Maybe a pinched cable somewhere in the wiring harness?

I've seen bikes that have worn rings that start well when cold, but after they heat up they lose compression and become hard to start. How much time is on the engine? Have you had much dirt pass through the filter?

mx317, on 09 March 2012 - 05:10 AM, said:

29 hours. I'm militant about air filters. I rotate through 4 different air filters, almost always changing them out every ride. That's not to say dirt didn't get passed at some point. I'll do a leak down test if it comes to that.

Could it be that the EFI "choke" is always on? So it's flooding when hot starting it.

I notice when my the temp gets above a hundred degrees outside and i have been riding all day my 250XC may take as many as two kicks to start. Not always but sometimes

it could be fuel pump, I had one crap out and was doing the same thing.  try giving it some throttle while kicking it and see it fires up

Update: repeated symptoms again today. Bike got hot, wouldn't kickstart BUT it fired right up when I bump started it. I repeated this half a dozen times. I really don't think I have a leaky valve or compression issue. It run great and I can tell when the compression is bad on a bike. It has plenty of power. Is there some disconnect between the kickstarter and the fuel pump? I'm not knowledgeable enough about the FI system to pinpoint what might be the culprit.

Justin Hambleton, on 09 March 2012 - 12:27 PM, said:

The speed of the kickstarter is the issue. It is not able to overcome your 'issue', and the motor needs more rpm's to start.
This is a classic leaking intake valve or bad ring symptom. Do a 'cheater' leak down test with compressed air.
Also replace your plug first, cause they are finicky...

Krannie, on 09 March 2012 - 05:49 PM, said:

It has a brand new spark plug. I always change them when I check valves. I have a friend with a leak down tester. I'll probably do that next. It would be rather discouraging if I already have a valve or piston ring issue at only 30 hours.

I think you've all helped narrow this down to at least something that makes sense. Thanks.

Edited by Justin Hambleton, 09 March 2012 - 06:58 PM.

I broke my ankle soon after this post, requiring surgery, so this issue got put on the backburner for awhile. A couple weeks ago I bit the bullet and ordered a new fuel pump. Mine was leaking ever so slightly from the main plastic tube that connects to the fuel line. I was told by an experienced race mechanic that this was a good sign the fuel pump was going bad. Whether or not it was a contributing factor is hard to say, but the new fuel pump fixed the problem, so take it for what it's worth. No more starting issues... $400 later.

Edited by Justin Hambleton, 11 June 2012 - 01:23 PM.