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Kdx220 Runs good for a sec with fuel valve off

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Been fighting this thing running right for some time. Kips is clean carb is immaculate. Jetting 42/145 needle in middle pos.  Air box tip toe new notoil filter. New boyesen reeds. 500' sea level. Bike hasn't ran right since i bought it. Starts first kick every time. But has no power whatsoever. Well I turned the fuel off today and right before it died it ran like a bat out of hell. I've tried adjusting float from the spec of 16mm all the way to 22mm and it has the same effect. Runs good right before it dies only. I would think it's the needle seat or float but like I said I've ran it way down and at spec and with fuel hooked up and bowl off the fuel stops flowing right when the float hits the needle valve. Tried it with an open air box still no change. Bike wont idle untill the bowl starts running out than it idles fine and a getting a couple good braps than she dies. 

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Out of curiosity, have you checked the exhaust/packing? Perhaps air flow on the exit side is the issue?
I've ran it without the silencer . No change. Need to run some water through the expansion pipe

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Let us know what happens after that. I’m trying to think what else it could be after everything you’ve already checked.

How about the kill switch? Have you disconnected that and started the bike, or checked the stator etc, to see if it’s a voltage thing?

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Let us know what happens after that. I’m trying to think what else it could be after everything you’ve already checked.

How about the kill switch? Have you disconnected that and started the bike, or checked the stator etc, to see if it’s a voltage thing?
Will do. Another forum A guy mentioned it being a timing issue waiting for flywheel puller in the mail. will check that out also. Has a brand new petcock as well.

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After all you’ve done on the mechanical side, it seems the only logical step is to now check the electrical. I’d definitely try running it with the kill switch disconnected, just to see if that’s faulty. They stall engines once they start to wear out. Also, you don’t necessarily need to remove the stator to check the timing setup you have. You can just remove the cover and look at the timing markings.

 

You could check the throttle position sensor on the Carb as well perhaps?

 

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After all you’ve done on the mechanical side, it seems the only logical step is to now check the electrical. I’d definitely try running it with the kill switch disconnected, just to see if that’s faulty. They stall engines once they start to wear out. Also, you don’t necessarily need to remove the stator to check the timing setup you have. You can just remove the cover and look at the timing markings.
 
You could check the throttle position sensor on the Carb as well perhaps?
 
Carb don't have a tps. I don't have to remove flywheel yo Check timing? I would think a bad kill switch would be all or nothing. I guess it. Would have some resistance. Easy enough to check. I'll oil out the coil also.

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Well, the flywheels usually have markings on them, to show whether you’re “advanced” or “pulled back”. You need to check you’re set to OEM specs (usually in the middle).

If you’re removing it to check actual wiring and resistance etc, that’s a different matter and is worthwhile in your situation.

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Little update - done a leak down test and it had no leakage over 5 min or so. But bike smokes like it's losing tranny fluid, and my tranny fluid level is dropping as well. So kinda scratching my head there. I've tried all sorts of jetting and needle heights to no prevail. Only time I've gotten it to run out right was with the float bowl way over adjustment. But the power band was unpredictable.

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Despite the test you mentioned in the very first post,

I'd still preventatively  replace the inlet needle and seat.

 

Even if the inlet valve appears to seal correctly by checking it the way you've described,

vibrations from when the engine is running might be keeping it slightly off the seat,

raising the fuel level in the carburetor and richening all metering circuits.

Edited by mlatour

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Despite the test you mentioned in the very first post,
I'd still preventatively  replace the inlet needle and seat.
 
Even if the inlet valve appears to seal correctly by checking it the way you've described,
vibrations from when the engine is running might be keeping it slightly off the seat.
Unfortunately the seat is not replaceable in the pwk33. I do have a new needle valve in it tho.

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Pretty sure I've read somewhere some folks 'polish' the old seat with a Q-Tip and mild abrasive to

remove any traces of debris stuck on and make it smooth again for a new needle to seal properly.

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Pretty sure I've read somewhere some folks 'polish' the old seat with a Q-Tip and mild abrasive to
remove any traces of debris stuck on and make it smooth again for a new needle to seal properly.
I'll give it another look, it looked to be very clean and hasn't any oxidation etc. I soaked everything in berrymans when I first got the bike. I'll try an get it a bit cleaner and pit it under a scope and see how bad the pitting is.

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Perhaps the soaking damaged some seals / o-rings ?

 

Not sure on that model carburetor but in particular the Keihin FCR found on most 4-stroke carbureted MX'er 

do not like to be soaked, they can even be finicky on the type of solvent used. (brake/parts cleaner)

 

Driveability issues from swelled seals (mid body gasket) which in this case cause an air leak

are somewhat a common problem for FCRs that have been damaged by soaking / cleaning.

Edited by mlatour

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Perhaps the soaking damaged some seals / o-rings ?
 
Not sure on that model carburetor but in particular the Keihin FCR found on most 4-stroke carbureted MX'er 
do not like to be soaked, they can even be finicky on the type of solvent used. (brake/parts cleaner)
 
Driveability issues from swelled seals (mid body gasket) which in this case cause an air leak
are somewhat a common problem for FCRs that have been damaged by soaking / cleaning.
You're completely right. On these particular carb there is an o-ring under the jet block. I did however replace it in the process. Very common problem on these carbs. That's the only thing not metal in the carb.

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