Kx450 hot start issue

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9/12/2018 5:23 AM

Some of you may know ive been chasing my tail with this 09 kx450f having starting issues. Ive had a dealer and kawasaki try to diag this bike with no success.

Ive narrowed the problem down to the bike only having starting issues when its hot. It starts cold no problem. 3 kicks and its running and stays running. The bike has passed all compression and leak down tests performed by the dealer and myself. Entire motor has 4 hours on it.

The ignition coil, spark plug cap, stator, rectifier, spark plug, killswitch, and ecu have all been replaced so far. I did replace the fuel pump, but it does have a small dribble from the outlet tube, and i want to think that could have an effect on the bike as it shouldnt leak. It seems weird that heat would make a difference here?

I guess im looking for some insight from more experienced guys like pawpaw or others on where to go with this thing. Can a bad coolant temp sensor cause this to happen?

Im about to order another fuel pump, coolant temp sensor, and fuel injector and see if that fixes it.

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9/12/2018 6:06 AM

It sounds like you have covered the bases for most causes of hot start issues.
Yes a bad coolant sensor will also cause it.
Does you bike have a tip over sensor? They do go bad also.
Your fuel leak can also cause fuel pressure issues.
Your injector can also have a very small leak that causes the bike to load up when shut off hot and cause hot start issues. Remember the old hot start lever on carb style 4 strokes?


Paw Paw

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9/12/2018 6:48 AM

Paw Paw 271 wrote:

It sounds like you have covered the bases for most causes of hot start issues.
Yes a bad coolant sensor will also cause it.
...more

I have swapped the tip over as well. No luck.

I did try to pull the high idle while the bike was hot in hopes it would act as pulling a hot start lever. No luck.

I do get a little bit of smoke from the exhaust that i dont get from my 250f, so i feel like the bike is running rich. If it helps, i have 2 ecu’s. One is stock and one is mapped by tokyo mods. The tokyo mods one was mapped to fix decel pop, im assuming they richened the map. That ecu does not allow the bike to start hot or cold. What this is leading me to believe and to kindof go along with what youre saying is: a combination of a leaking pump, potentially leaking injector, or a faulty coolnt sensor is causing an overly rich condition that prevents hot starting.

Ill also note, i was able to turn it off and IMMEDIATELY restart it, but was not able to if i let the bike sit for 3-5 mins.

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9/12/2018 7:33 AM

Yes that points to a rich condition. If the injector is even leaking a small amount it may have no effect on cold starting as it needs a richer condition to start good cold, but when hot it will cause an over rich condition that will make it hard to start. When hot, try holding the throttle wide open to help lean it out to see if it helps.

Paw Paw

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9/12/2018 7:54 AM

Alright thanks for the input. Ill start by replacing the fuel pump and coolant sensor. If i still have issues ill go ahead and grab an en entire throttle body assembly from ebay - theyre the same price as a new injector from RM. that way i can rule out any potential throttle body issues at the same time. I know the 09s had some kind of issues.

If i remember ill report back as to what the fix is.

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9/12/2018 8:05 AM

kb228 wrote:

Alright thanks for the input. Ill start by replacing the fuel pump and coolant sensor. If i still have issues ill go ahead and ...more

The throttle body issue on the 09 was for the inlet (where the airboot clamps) cracking due to a casting issue. They replaced it with an updated part in a recall. There was also an issue with footpeg springs and/or pins (don’t recall which).

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9/12/2018 8:40 AM

kb228 wrote:

Alright thanks for the input. Ill start by replacing the fuel pump and coolant sensor. If i still have issues ill go ahead and ...more

omalley wrote:

The throttle body issue on the 09 was for the inlet (where the airboot clamps) cracking due to a casting issue. They replaced ...more

Wonder if that crack lets air in & throws off the air flow sensor or air pressure sensor. We will see.

Also, thanks for the info but i dont think my foot peg springs and pins are causing the bike to not start. Haha jk

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9/12/2018 9:23 AM
Edited Date/Time: 9/12/2018 9:24 AM

You may want to consider picking up a Motion Pro injector cleaning tool. For me I would invest in the tool rather than picking up a used throttle body of unknown heritage.
https://www.rockymountainatvmc.com/p/989/52831/Motion-Pro-Fuel-Injector-Cleaner-Kit-HYB

Paw Paw

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9/12/2018 9:27 AM

Is there a way i can tell its leaking before i spend the money? Can i rig up a tube and syringe and apply pressure to see if gas comes out?

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9/12/2018 9:39 AM
Edited Date/Time: 9/12/2018 9:48 AM

If possible...Pull the injector from the throttle body when the engine is fully warmed up, leaving the full line attached and see if drops of fuel show up over a few minutes of time. It only takes a few drops to cause the starting issue.
I do still strongly suggest the use of the injector cleaning tool as the best way to do the job, plus you can also get paid by folks to clean their injectors and thus the tool will pay for itself. Watch the video of the tool in action.

Paw Paw

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9/12/2018 10:01 AM

Paw Paw 271 wrote:

If possible...Pull the injector from the throttle body when the engine is fully warmed up, leaving the full line attached and ...more

What i could do is do the syringe idea and heat the injector with a heat gun to 120 degrees or so. That could simulate a hot engine. And doesnt the fuel pump hold some pressure after the bike is off?

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9/12/2018 10:34 AM

kb228 wrote:

Some of you may know ive been chasing my tail with this 09 kx450f having starting issues. Ive had a dealer and kawasaki try to ...more

Try the coolant temp sensor first (cheapest of your three potential orders from the last line). Had a 14' KX450F that wouldn't run properly with a Vortex (limp mode, rich condition) and exhibited similar starting issues once hot. Good info in this thread as well:

http://www.proride.com/smfforum/index.php?topic=75295.0


SoCal local so I ended up at the shop listed on Page 3; never had a problem after that.

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9/12/2018 10:53 AM

kb228 wrote:

Some of you may know ive been chasing my tail with this 09 kx450f having starting issues. Ive had a dealer and kawasaki try to ...more

crc245 wrote:

Try the coolant temp sensor first (cheapest of your three potential orders from the last line). Had a 14' KX450F that wouldn't ...more

I appreciate the info man. I will be ordering a pump and sensor today. My pump leaks, its broken, might as well fix it. Im hoping i dont have to fart around with the injector.

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9/12/2018 11:15 AM
Edited Date/Time: 9/12/2018 11:19 AM

Paw Paw 271 wrote:

If possible...Pull the injector from the throttle body when the engine is fully warmed up, leaving the full line attached and ...more

kb228 wrote:

What i could do is do the syringe idea and heat the injector with a heat gun to 120 degrees or so. That could simulate a hot ...more

it definitely sounds like an overly rich condition as stated before... If it’s not a simple sensor fix; then I second his idea as the best way to test to see if the injector is hanging open when warm... mainly because it would be the easiest way to mimic the actual conditions that are occuring...I also love the motion pro injector tool it’s great investment if you’re working on a lot of fuel injected bikes...

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9/12/2018 12:09 PM

Alright guys the sensor and pump are on the way. Will report back when i know something. Appreciate the help

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9/12/2018 3:27 PM

Heres some info.

Today, the bike starts and runs as normal. Let it get nice and warm, let it sit for 5-10 mins and it starts up. Definitely weird. Still moving forward with the sensor and stuff. They dont fix themselves.

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9/13/2018 4:07 PM

So i got the new coolant temp sensor installed. The ecu that previously wouldnt allow the bike to run, now lets the bike run. Lets just say i was too happy to care about annoying my neighbors. Will be at the track saturday to confirm. Photo

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9/14/2018 6:33 AM

Where is your helmet?

Paw Paw

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9/14/2018 7:45 AM

I got the new shoei clear helmet

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9/18/2018 6:17 PM

Well guys i got to ride the bike for a total of 20 mins until i crashed and broke my tibia and collarbone. It worked the entire time and the guy who rode it back to my truck had no issues getting it going.

Wont be till spring before i can ride it again. So for now i feel confident that the coolant sensor did the trick

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9/18/2018 7:12 PM

Sorry to hear that. Get well soon. ( So that new clear helmet works ok then. ha ha)

Paw Paw

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9/18/2018 7:13 PM

Paw Paw 271 wrote:

Sorry to hear that. Get well soon. ( So that new clear helmet works ok then. ha ha)

Paw Paw

Works great! No head injuries!

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