2010 KX450F Bogging down - Kawasaki Forum :: KawasakiWorld.com
 
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post #1 of 9 Old 06-29-2013, 06:53 PM Thread Starter
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2010 KX450F Bogging down

Hi all,

I'm having a serve issue where my bike (2010 KX450F) is bogging down and backfiring bad after the top end was rebuilt (only piston rings were replaced, valves weren't touched)

Heres a video of what its doing:

I had this problem when i first rebuilt my topend 3 months ago and i ended up fixing it by cleaning out the air idle passageway in the throttle body as it was gunked up with air filter oil. But ever since i had to replace a blown head gasket 4 weeks ago its doing the same thing but my throttle body is spotless. My bike has been at the dealers workshop for the past 3 weeks and got it back yesterday after they told me to put a new rear tire on as they thought because it was loosing traction so easily that it was messing with the cdi box?? Threw a new tire on but not to my surprise this didn't fix a thing. It worked good for the first 30 mins but got worse and worse the more i rode it and happens more frequently if im going over rough terrain, whoops or going up the upramp of a jump (still don't know how i managed to save the nose dive ). It happens randomly though - one minute it will work good the next its almost unridable so this is pointing to electrical/EFI issues. So if anyone else has any ideas what it could be i would love to know, here is a list of what the dealer has checked:
All electronics and sensors show that they are fine with not faults on the diagnostics kit
Air temp sensor and air box was cleaned
All wiring has been checked for any wires touching or shorting out
Changed spark plugs
Entire throttle body cleaned
All electrical contacts cleaned
Fresh Fuel
Fuel pump filter screen from what I can see is clean
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post #2 of 9 Old 06-29-2013, 07:11 PM
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So, before you changed the rings this problem wasn't happening? And the head gasket ruptured since then?
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post #3 of 9 Old 06-29-2013, 09:32 PM Thread Starter
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Correct Hagrid, the bike was running perfect before i rebuilt it. The head gasket failure was caused due to a little bur on top of the barrel mating surface and a cheap head gasket, was easily fixed by the mechanic with a bit of sandpaper on a mirror and a OEM gasket. I'll give abit of a history with what happened:

70hrs - Top end rebuild (only changed rings as valves were perfectly in spec) Took it for a ride and had the bogging down issue, checked the throttle body and noticed the air idle passage way was gunked up with air cleaner oil. Cleaned it and fixed the problem

74hrs - Blew head gasket, replaced head gasket with same cheap one as i thought i torqued the head bolts incorrectly

90hrs - Blew gasket again noticed head gasket failure was caused due to a slight bur ontop of barrel mating surface, sanded surface flat and used genuine head gasket and base gasket. And this is as far as i have got now as i got the bogging issue.

My bike has never been on a race track, always serviced at 5hrs intervals and never had the arse flogged out of it.
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post #4 of 9 Old 06-30-2013, 04:26 AM
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Well... for 24 hours (between 74 and 90) the bike ran fine, yes? I think your hunch regarding an electrical fault is valid.

What's it like at wide open throttle when it bogs? Does it die or will it climb out of the bog condition?
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post #5 of 9 Old 06-30-2013, 06:50 AM Thread Starter
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yep it ran perfectly for the 24 hours. The bogging usually happens around 1/4 throttle but sometimes even up to 3/4 throttle, when it fully bogs if i pull the clutch it idles perfectly as if nothing is wrong, and if i hold the throttle wide open it will bog but then about half a second later it will climb out and hit full power.
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post #6 of 9 Old 06-30-2013, 08:41 AM
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If you have the shop manual and a multimeter I would start checking sensor outputs and resistances.

This smells like a Throttle Position Sensor intermittent failure. Or, the stick coil insulator for the spark plug is breaking down.

Last edited by hagrid; 06-30-2013 at 08:44 AM.
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post #7 of 9 Old 06-30-2013, 04:46 PM
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Do check all electrical connections that have been disrupted. Air leak around the intake boot to the TB is a possibility.
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post #8 of 9 Old 07-01-2013, 02:26 AM Thread Starter
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I and the mechanics at my local kawasaki dealer have checked all the sensors according to the workshop manual and they all check out fine. The air intake boot is properly sealed and i made sure that i tightened the crap out of the clamp last time. All electrical connections are fully connected and clicked together, i might try and run a continuity check with a mulimeter lead from the plug and the other multimeter lead all the way back to the ECU to check if there are any cracked wires.

Thanks for all your help so far everyone! Its much appreciated and if you can think of any other possibilities please let me know
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post #9 of 9 Old 07-01-2013, 05:06 AM
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Just thinking about the video and the lack of throttle response demonstrated by the blipping. My WR400F has a carb with an accelerator pump. This pump squirts a shot of fuel for the low RPM rapid throttle openings. It works. Now, with the FI what takes the place of the accelerator pump? I'm suspecting it is in the ECU programing, right? So, if the ECU is sensing the rapid the rapid throttle openings is should compensate with a blast of fuel through the injector, right? As mentioned earlier, the TPS could be intermittently faulty. Also, debris in, or near, the injector could be possible.
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