2011 KX 450 Starting Issues

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3/8/2012 5:20 PM
Edited Date/Time: 3/8/2012 5:29 PM

Ok KX experts... I have a major head scratcher. I have a 2011 KX450 with 29 hours. The valves are in perfect spec. It fires right up when cold, but as soon as it reaches operating temperature, it will NOT start. I kick and kick and kick and it won't start. I've checked stator resistance and it's in spec. I took it to a dealer to have them check the FI for error codes and it showed nothing. Like I said, the bike starts right up just fine when it's cold, but as soon as it reaches a certain temperature, it will not start.

I've double checked the valves and they are perfect. It's either an electrical or fuel problem, I just have no idea how to narrow it down. Hoping someone else may have had this issue with a FI KX450. Starts fine cold, won't start when hot? Why the hell not?! I'm at my wits end. I don't know where to go from here other than disconnect everything and reconnect. I do have a remapped ECU, but it's been remapped since 5 hours and ran perfectly fine up until 24 hours or so. When the bike is started it runs perfectly fine. Doesn't cut out, perfectly crisp throttle, but as soon as I shut it off, it will not start again.

I would buy someone the hottest stripper in the land if they can help me diagnose this problem.

As a side note: one other new issue I've also noticed is that when I disconnect the fuel pump from the bike, it leaks right at the little black tube that comes off the fuel pump. It never did this before. It's almost as if there's a valve or something messed up in the fuel pump. This is giving me cause to believe perhaps the bike is getting too rich? I don't even know if that makes sense, but fuel shouldn't be flowing out of the pump unless it's running.

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3/8/2012 6:21 PM

Does it run as long as you want it too? Like to ride for a half hour? And then when you try to start it hot, it won't run? Check for spark at that time. If it's got spark, then it's a fuel problem. If not it's an electrical problem. A cold stator can check out fine, but when it gets hot, it can fail. That's what they do. Happened to me twice. Not saying that's the problem, but you have to eliminate the easiest ,and follow a logical diagnostic approach. Try what I said, and see what the findings are.

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3/8/2012 6:31 PM
Edited Date/Time: 3/8/2012 6:31 PM

mx5471 wrote:

Does it run as long as you want it too? Like to ride for a half hour? And then when you try to start it hot, it won't run? Check for spark at that time. If it's got spark, then it's a fuel problem. If not it's an electrical problem. A cold stator can check out fine, but when it gets hot, it can fail. That's what they do. Happened to me twice. Not saying that's the problem, but you have to eliminate the easiest ,and follow a logical diagnostic approach. Try what I said, and see what the findings are.

Yeah, it will run perfectly fine until I shut it off. I'll do 15-20 minute motos and it runs like a champ. As soon as it shuts off, no start again. I checked stator resistance when it was cold and hot and the ohms were in spec in both instances.

I'm going to go through all the connectors tonight, make sure nothing is loose, use dielectric grease and go from there. Frustrating.

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3/8/2012 9:01 PM

crack the throttle just a hair..

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3/9/2012 8:22 AM

aaaah these temperamental four strokes. From my experience my bike doesn't like any fuel under 93 octane and it can't be more than a week old. I have in the past had "bad gas". Drained the tank. Put new fuel in it - BA BOOM - fired right up. Just a thought, but my philosophy is check the simple stuff first.

i know your bike is fuel injected - do the EFI bikes have "hot starts"? just out of curiosity. I have the same issue with 15-20 minute rides. My bitch gets hot hot hot. then doesn't want to start for a little bit after that.

Good luck dude.

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3/9/2012 8:29 AM

You need to explore that fuel drip further. Does the bike restart again after it cools to normal temperature?

Your flashed ECU may be too rich for hot starting. When the engine is hot, it needs more air.

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3/9/2012 10:07 AM
Edited Date/Time: 3/9/2012 10:12 AM

mxtech1 wrote:

You need to explore that fuel drip further. Does the bike restart again after it cools to normal temperature?

Your flashed ECU may be too rich for hot starting. When the engine is hot, it needs more air.

Yes, it does restart just fine once it cools off.

The ECU mapping I have now is straight from the Kawi off-road team and it's actually a bit leaner so I run (usually) a 50/50 mix of 110 and 91, but sometimes a bit heavier on the 110. If I don't run race gas, it can detonate under a heavy load. I do want to reflash it, perhaps going back to stock or maybe one of the mappings Precision Concepts has for their off-road race bikes. I want to be able to go to Baja and not worry about running high octane gas.

I did remove the fuel pump awhile back and partially disassembled it (i.e. removed the outer rubber bladder and pulled off the fuel filter). It seemed relatively harmless and straightforward. I took it apart because I run a dry break and thought I might have introduced a small amount of dirt from the dump can. It was perfectly clean and void of any dirt particles. It went together just fine. The weeping is obviously not right, which leads me to believe it may be a fuel pump issue. I probably shouldn't have touched it.

It's just weird that the temperature is a factor. I can't quite pinpoint why that would be the case and how that would affect the fuel pump other than creating a super rich condition, like you suggested.

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3/9/2012 12:25 PM

Update: I ran it for about 10 minutes, got it up to operating temperature killed it and it would not kickstart per usual. However, it fired right up when I bumpstarted it. I repeated this half a dozen times. No kickstart, but would bumpstart.

It only has 29 hours on the motor, but good god, do I have a leaky valve or is there something electrical happening between the kickstarter and the fuel pump?

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3/9/2012 12:59 PM

Temor a la Mancha wrote:

Update: I ran it for about 10 minutes, got it up to operating temperature killed it and it would not kickstart per usual. However, it fired right up when I bumpstarted it. I repeated this half a dozen times. No kickstart, but would bumpstart.

It only has 29 hours on the motor, but good god, do I have a leaky valve or is there something electrical happening between the kickstarter and the fuel pump?

when you report something like this it leads me towards valve train

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3/9/2012 1:47 PM

mxtech1 wrote:

when you report something like this it leads me towards valve train

Yeah, unfortunately my gut tells me valve train as well. The symptoms just don't quite add up to an electrical problem. It's just odd that the valves are in spec. I'll check them again. (L) intake was a tiny bit off spec - I think .001" or so. I'll double check again.

Thanks for the tips. Much appreciated.

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6/28/2014 9:04 AM

My 2012 kx450f is doing the same thing! it starts and runs just fine but once it gets hot and i turn it off the bike will not start again for about 15-20 min. Did you ever figure out how to fix it?? please help! the bike only has 66 hours!

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6/28/2014 7:05 PM

Temor a la Mancha wrote:

Yeah, unfortunately my gut tells me valve train as well. The symptoms just don't quite add up to an electrical problem. It's just odd that the valves are in spec. I'll check them again. (L) intake was a tiny bit off spec - I think .001" or so. I'll double check again.

Thanks for the tips. Much appreciated.

check your temp censor . bet its thats. good way to tell. when the bikes gets hot after your moto, crack the throttle to around quarter throttle and give her a kick. good chance she will fire up then. theres is no code for the temp censor. you have to go by knowledge or be able to hook your bike up to the comp as soon as you get done with your moto.


@Haven024 same goes for you, check your temp censor.

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6/30/2014 9:48 AM

new water temp sensor

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2/23/2015 10:16 PM

Temor or Haven: did either of you solve the problem? My bike started doing the same thing in the late fall and I thought it was bad fuel. I have tried a couple things as well as checking valves and cleaning the air temp sensor and nothing has helped. Any advice?

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2/24/2015 3:20 PM
Edited Date/Time: 2/24/2015 3:29 PM

Tazao wrote:

Temor or Haven: did either of you solve the problem? My bike started doing the same thing in the late fall and I thought it was bad fuel. I have tried a couple things as well as checking valves and cleaning the air temp sensor and nothing has helped. Any advice?

for my bike it was a valve problem, i had one exhaust valve out of spec it was to tight. so when the bike got to normal running temp the shim would expand and once i turned it off it wouldnt start tell i cooled back down. so i put in a thinner shim and it fixed the problem right away. hope this helps, good luck. also my buddy is a certified Kawasaki mechanic and he sets his exhaust valves on the lose side of spec for that very reason.

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5/31/2016 7:24 AM

I will add to this ancient thread: there is a small rubber seal/o-ring on the tank mounted fuel pump flange that the fuel pump outlet pups into. fuel (under pressure) flows through this o ring and out the high pressure line. if this seal/o ring deal is not doing its job , pressure is lost straight back into the tank. I have had this happen before. hard starting due to lack of fuel pressure. I replaced the little rubber seal that was obviously not creating a tight seal, problem solved

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