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Discussion Starter #1
Hello everyone. I'm new to the forum. My kfx 450 won't start using the electric start. I can bump start it just fine but it'll struggle to idle and miss every now and then at low rpms. I've checked the decompression spring and set the tps to correct voltage and tested the rollover sensor as well. Anyone have an idea what could cause this problem?
 

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Welcome to the Forum...!!

Make sure your battery is fully charged 12.8v standard...!!

Have you tried adjusting your idle with the idle knob shifter side of the throttle body...???.If yes!

Check your valve clearance...
Valve Clearance: between cam and valve lifter
Standard:
Exhaust 0.17 ∼ 0.22 mm (0.0067 ∼ 0.0087 in.)
Inlet 0.10 ∼ 0.15 mm (0.0039 ∼ 0.0059 in.)
If the valve clearance is not within the specified range,
adjust it.
 

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Discussion Starter #3
Welcome to the Forum...!!

Make sure your battery is fully charged 12.8v standard...!!

Have you tried adjusting your idle with the idle knob shifter side of the throttle body...???.If yes!

Check your valve clearance...
Valve Clearance: between cam and valve lifter
Standard:
Exhaust 0.17 ∼ 0.22 mm (0.0067 ∼ 0.0087 in.)
Inlet 0.10 ∼ 0.15 mm (0.0039 ∼ 0.0059 in.)
If the valve clearance is not within the specified range,
adjust it.
Tried starting with a full battery yesterday while doing all the tests. Valve clearances are at .18 for exhaust and .10 for intake. Haven't tried the idle knob yet. Any chance it could be the ECU? Or possibly temp sensor? It had a dynatek digital ignition on it previously. Have taken it off to try and find the problem
 

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Tried starting with a full battery yesterday while doing all the tests. Valve clearances are at .18 for exhaust and .10 for intake. Haven't tried the idle knob yet. Any chance it could be the ECU? Or possibly temp sensor? It had a dynatek digital ignition on it previously. Have taken it off to try and find the problem
Are both intake valve 0.10mm...??

The 0.10 mm is a problem(too close) doesn't allow the valve to completely close thus loss of compression, gets worse when the motor's hot...Both valves needs to be adjusted out to 0.13 ~ 0.14 mm (best performance)

The Exhaust 0.18 mm will be a problem soon..should be adjusted out to 0.20 ~ 0.21 mm (best performance).
 

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Discussion Starter #5 (Edited)
I agree with you those specs would be best. But that shouldn't hinder it from starting I wouldn't think or cause it to miss on low rpms. It acts up more when cold than when hot. When it's hot I can occasionally get it to fire up with the e-start.
[UPDATE] Is it possible for it to be the fuel pump? I'm getting just about 50ml of fuel in 3 seconds of the pump turning at the most.
[UPDATE 2] Anyone think this could be caused by low compression? I put a few drops of oil down the sparkplug hole and it seemed to be closer to firing up if that makes sense. It would occasionally backfire and turn over quicker as if it were just about to fire up
 

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I agree with you those specs would be best. But that shouldn't hinder it from starting I wouldn't think or cause it to miss on low rpms. It acts up more when cold than when hot. When it's hot I can occasionally get it to fire up with the e-start.
[UPDATE] Is it possible for it to be the fuel pump? I'm getting just about 50ml of fuel in 3 seconds of the pump turning at the most.
[UPDATE 2] Anyone think this could be caused by low compression? I put a few drops of oil down the sparkplug hole and it seemed to be closer to firing up if that makes sense. It would occasionally backfire and turn over quicker as if it were just about to fire up
You might have one or more problems going on...
1 your valves need to be adjusted...!!!
2, Yes your fuel pump strainer might be dirty/clogged...
3 you might have a faulty coolant sensor..
 

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Discussion Starter #7 (Edited)
You might have one or more problems going on...
1 your valves need to be adjusted...!!!
2, Yes your fuel pump strainer might be dirty/clogged...
3 you might have a faulty coolant sensor..
Will check the coolant sensor. I checked the fuel pump strainer. It looks to be dirty but actually has a big hole in it 🙄 so fuel flow shouldn't necessarily be restricted? It was also flashing a code at me for the fuel injector but the injector works fine and the wires are all fine. It has stopped showing the code tho. That one didn't really make sense to me
[UPDATE] Rechecked the valves after thinking I probably got mixed up on the clearances. Intake is at .14~.15 exhaust is at .19~.20
And like I said it actually works better when it's hot than cold so I don't suspect the clearances to be an issue
 

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Discussion Starter #9
Test your injector for being faulty if it's coding it...
I already tested the injector. Resistance was within range as well as input voltage and output voltage. Sprays fuel when trying to start as it should. The code only flashed a few times then just went away. Pretty certain it's not the injector.
My suspicions are the following: temp sensor, fuel pump, low compression (possibly due to leaking valves), or faulty tps.
 

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I already tested the injector. Resistance was within range as well as input voltage and output voltage. Sprays fuel when trying to start as it should. The code only flashed a few times then just went away. Pretty certain it's not the injector.
My suspicions are the following: temp sensor, fuel pump, low compression (possibly due to leaking valves), or faulty tps.
Leaky valves +++++++ to be a major problem..!!!!

TPS maybe bouncing out of range due to a tight throttle cable that will throw your ECU into error code...make sure there a little slack in the throttle cable to prevent it from bouncing

Yes a faulty water temp will play havoc with your fuel setting...dirty fuel pump strainer will cause low fuel pressure,

Another possibility to add to your suspicions is the vehicle down sensor...!

see pic for location
 

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Discussion Starter #11
Leaky valves +++++++ to be a major problem..!!!!

TPS maybe bouncing out of range due to a tight throttle cable that will throw your ECU into error code...make sure there a little slack in the throttle cable to prevent it from bouncing

Yes a faulty water temp will play havoc with your fuel setting...dirty fuel pump strainer will cause low fuel pressure,

Another possibility to add to your suspicions is the vehicle down sensor...!

see pic for location
Already tested the vehicle down sensor and it checked out okay. Will check again tho. Do you know how much fuel the fuel pump should be putting out in 3 seconds? I read somewhere that it should be over 50ml. Not sure if that's accurate tho.
Also I'm not certain that the valves are leaking yet. The exhaust sucks in a little air before blowing air out. Do these engines have slight valve overlap? If not then I'm pretty sure the valves are leaking
 

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Already tested the vehicle down sensor and it checked out okay. Will check again tho. Do you know how much fuel the fuel pump should be putting out in 3 seconds? I read somewhere that it should be over 50ml. Not sure if that's accurate tho.
Also I'm not certain that the valves are leaking yet. The exhaust sucks in a little air before blowing air out. Do these engines have slight valve overlap? If not then I'm pretty sure the valves are leaking
Sure, see picture
 

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Discussion Starter #13 (Edited)
Sure, see picture
Checked the temp sensor at 32 F and 104 F. The ohm reading was jumping all over the place and mostly staying in megaohms with occasionally jumping to kilohohms. So maybe I've found what's causing all this?
[UPDATE] Checked fuel pressure just now. Pressure dips down to 30psi when I give it throttle and rises to 40 when I let off. Pretty safe to say it's the fuel pump? Or could the temp sensor or ECU be messing with the pump?
 

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Checked the temp sensor at 32 F and 104 F. The ohm reading was jumping all over the place and mostly staying in megaohms with occasionally jumping to kilohohms. So maybe I've found what's causing all this?
[UPDATE] Checked fuel pressure just now. Pressure dips down to 30psi when I give it throttle and rises to 40 when I let off. Pretty safe to say it's the fuel pump? Or could the temp sensor or ECU be messing with the pump?
No the ECU controls the pumps relay to turn it on/off not the pump it's self... 30 psi it's a bad pump..there cheap on ebay.. New 35mm Fuel Pump Fits for Kawasaki KFX450R / KSF450-BAF 2008-2013 | eBay

This thread will help you replace the fuel pump How to clean fuel pump
 

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No the ECU controls the pumps relay to turn it on/off not the pump it's self... 30 psi it's a bad pump..there cheap on ebay.. New 35mm Fuel Pump Fits for Kawasaki KFX450R / KSF450-BAF 2008-2013 | eBay

This thread will help you replace the fuel pump How to clean fuel pump
Do those cheap fuel pumps actually hold up? Been seeing a lot of those on eBay. Saw a quantum fuel pump that looked promising but if those cheap ones actually get the job done and won't quit then I'd be saving quite a bit of money there
 

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Do those cheap fuel pumps actually hold up? Been seeing a lot of those on eBay. Saw a quantum fuel pump that looked promising but if those cheap ones actually get the job done and won't quit then I'd be saving quite a bit of money there
I have a cheap replacement in mine...good so far..this one is a little more but you get a new regulator, wires & O-rings with the pump... Brand Kawasaki KFX450R Quad ATV Intank Fuel Pump 2008-2013 49040-0020 | eBay

A new fuel pump from Kawasaki is $433.00 NEW 2008 - 2014 GENUINE KAWASAKI KFX 450R FUEL PUMP ASSEMBLY 49040-0020 | eBay
 
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