Hot start issues 450 kxf 2011

Gaetan47400
Edited Date/Time 7/10/2020 9:57am
Hi everyone,

I am having troubles with my 450 kxf 2011, and I really cannot figure it out:
- when cold, it starts perfectly well. If I turn it off it will start with the first kick every time
- once hot, engine runs perfectly
- if I stop when hot, it might restart at first kick, but if it doesn't, the bike is absolutely impossible to start. I could kick 100 times until being totally exhausted, nothing happens...
- however, if I jump start it, it will start at the 2nd compression everytime. The problem is when I'm alone in the forest, on the mud, impossible to jump start and I have to wait an hour...
- if it cools down, it restarts at first kick again

So far, I have checked my valve clearance: it was to small so I changed the shims, but the problem is exactly the same (I actually have a bit too much clearance at the intake now ...)

I have checked the capacitor: seems ok, plus I have replaced it with a 12V battery: problem is the same: won't start when hot

I have checked the ECU for any diag: nothing

I have tried to heat it up, then check the spark: there is a spark so I don't think it is a loss of spark (plus, as I said, it start well with jump start) (however, I have heated up the engine reving it in my garage, and the spark plug was completely black. I don't know if this is normal. But usually the spark plug is brown and clean so I don't think that I have a A/F issue)

Any ideas ?
I am lost here...
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Polishhammer 6/9/2020 4:57pm
6/9/2020 4:57pm
Valves are too tight or the stator is acting up. Most likely it’s the valves needing shimmed
Gaetan47400 6/10/2020 1:06pm
6/10/2020 1:06pm
Polishhammer wrote:
Valves are too tight or the stator is acting up. Most likely it’s the valves needing shimmed
Valves too tight: you mean valve clearance ? I had not enough clearance, and now i have too much, but the starting issue is the same. i have ordered new shims to be in the tolerances...

What do you mean by "the stator is acting up" ?

I have also ordered a new spark plug,but i don't think it will change anything since cold start is ok, and engine running hot too...
Polishhammer 6/10/2020 1:39pm
6/10/2020 1:39pm
If the valves are out of spec and they are are too tight, as the engine heats up the metals expand making the clearance even tighter or no clearance at all which in turn will not allow them to fully close. The engine will then be hard to start or not start at all when it is hot.
A bad ignition stator will sometimes work fine when the engine is cold, but when it gets hot it won’t have sufficient spark to allow the engine to start easy.
kb228
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kb228 6/10/2020 2:37pm
6/10/2020 2:37pm
Swap the coolant temp sensor. Its in a terrible location on these kawis and is prone to getting dirty/destroyed. Had a very very similar issue to yours on my 2009 kx450 and the sensor fixed it. I spent months chasing it and no local shops could diagnose it - even the kawi dealer.

The Shop

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Gaetan47400 6/10/2020 2:45pm
6/10/2020 2:45pm
kb228 wrote:
Swap the coolant temp sensor. Its in a terrible location on these kawis and is prone to getting dirty/destroyed. Had a very very similar issue to...
Swap the coolant temp sensor. Its in a terrible location on these kawis and is prone to getting dirty/destroyed. Had a very very similar issue to yours on my 2009 kx450 and the sensor fixed it. I spent months chasing it and no local shops could diagnose it - even the kawi dealer.
thanks, that could explain my problem. When you had this issue, didn't your ECU raised a fault code? And the sensor itself wasn't like an open circuit when testing it with a multimeter ?
kb228
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kb228 6/10/2020 4:32pm
6/10/2020 4:32pm
kb228 wrote:
Swap the coolant temp sensor. Its in a terrible location on these kawis and is prone to getting dirty/destroyed. Had a very very similar issue to...
Swap the coolant temp sensor. Its in a terrible location on these kawis and is prone to getting dirty/destroyed. Had a very very similar issue to yours on my 2009 kx450 and the sensor fixed it. I spent months chasing it and no local shops could diagnose it - even the kawi dealer.
Gaetan47400 wrote:
thanks, that could explain my problem. When you had this issue, didn't your ECU raised a fault code? And the sensor itself wasn't like an open...
thanks, that could explain my problem. When you had this issue, didn't your ECU raised a fault code? And the sensor itself wasn't like an open circuit when testing it with a multimeter ?
No codes, and nothing showed up on the dealers kawasaki computer. No open circuits.
Paw Paw
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Benton, LA US
Paw Paw 6/11/2020 4:38am
6/11/2020 4:38am
Cam chain wear will also cause this.
A leaking fuel injector will also cause this.

Paw Paw
Gaetan47400 6/11/2020 4:45am
6/11/2020 4:45am
Paw Paw wrote:
Cam chain wear will also cause this.
A leaking fuel injector will also cause this.

Paw Paw
Chain tensionner is alsmost half way. Enought to provoke this?
how do you check for fuel injector leakage ? If i connect a 12v battery with the fuel pump running, should i see fuel exiting the injector ?
Gaetan47400 6/11/2020 9:49am
6/11/2020 9:49am Edited Date/Time 6/11/2020 11:37am
Paw Paw wrote:
Cam chain wear will also cause this.
A leaking fuel injector will also cause this.

Paw Paw
When I plug a 12V battery I have an injection every time. I suppose it is normal as when pressing the kick, one of the first thing you need to do when you get voltage is to inject fuel for the incoming compression. However, when I plug the battery for the first time, the fuel spray is very weak, sometimes no fuel is coming out. If I do it again hafl a second later I got a nice spray. But if I wait 5s, the spray is shitty again. Is this what you mean by fuel injector leak = backflow in the injector = quick loss of pressure ?

Stator static test OK. Couldn't check the AC voltage with engine running: I tried to connect the harness with electric wires but then I cannot start the bike... probably the surface contact is very poor on the male side. I need to figure out a better way to connect intermediate cables to measure the voltage

Water temperature sensor resistance is in range at room temp (I ll check later when hot)

I have tested the regulator, and I got very weird results (attached image): maybe a casual Ohm tester isn't good for this test, and the kawa tester does something different ?





Paw Paw
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Paw Paw 6/11/2020 12:16pm
6/11/2020 12:16pm
If the injector is leaking it will allow fuel to flow into the intake when the engine is shut off. This then creates a very rich condition when you try to start it. A small partical of dirt can cause the injector to not close and seal as it should. A worn injector will do the same thing.
A worn cam chain will alter the valve timing just enough to cause hard starting, but the engine will still perform very close to normal when it does run.
Have you replace the cam chain?
Valves can be shimmed correctly , but still a worn valve will not seal thus causing hard starting and again it will run well when it is running.
You need to address all three of these.

Paw Paw
Gaetan47400 6/12/2020 3:02am
6/12/2020 3:02am
Polishhammer wrote:
If the valves are out of spec and they are are too tight, as the engine heats up the metals expand making the clearance even tighter...
If the valves are out of spec and they are are too tight, as the engine heats up the metals expand making the clearance even tighter or no clearance at all which in turn will not allow them to fully close. The engine will then be hard to start or not start at all when it is hot.
A bad ignition stator will sometimes work fine when the engine is cold, but when it gets hot it won’t have sufficient spark to allow the engine to start easy.
I could finally measure the AC voltage. Here are the values when engine is cold. When engine is hot there where approximately the sames, slightly lower (my pc crashed before I could save the values ...).

I've got a 2008-2010 workshop manual which indicated that the voltage should be above 29V. I guess it is the same range for the 2011 450 kxf ?
However I still get 14V at the capacitor connections. I would have expect less accordingly to my 70% drop in AC voltage.

Nevermind, I will order a new flywheel...





Gaetan47400 7/10/2020 9:57am
7/10/2020 9:57am Edited Date/Time 7/12/2020 10:20am
Hi all,
I replaced the flywheel, and I still get around 10v AC instead of 29... I don't get it...

I've got the exact same values. Can a stator produce less voltage, despite having the resistance values in the specified ranges?

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