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Kdx220 Jetting Problem

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#1
I have a 1997 kdx220 that just received a new wiseco piston, rings, gaskets, crank bearings, crank seals, and a good carburetor cleaning.

the cylinder is round, and true within .002" everywhere.

boyson reeds
FMF gnarly
FMF Rev arrestor
142 main
40 idler
3rd clip on the needle
float height exactly 16mm
fresh 32:1 mix in the tank
150psi compression test
no leaks from crankcase
no transmission fluid loss
no leaks around intake boot or air box

symptoms:
air screw does nothing, with 35/38/40/42 idler
and the idle screw similarly does not effect the bike, with any of those jets installed

idle is low, slow, and inconsistent
choke kills the engine if idling



moving the needle clip from second from bottom to second from top changes the bikes running, but only worse than third clip position


off idle (first 1/8 throttle) produces a pitiful lag/bog/hesitation, that is lessoned with the 40 pilot, but worsened with the others.

deceleration means burbling and coughing.

ice even changed arrestors from the woods to the Rev, no difference at all.


radiators are full, not leaking, and burped at the head and the left burper.


well, what do you think?
 
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#5
strip a bread twist tie and use its metal to clear out the passageway from the idle jet to the throat of the carburetor. enter from beneath and from above.

yes, it's clear. you can barely make out the wire in this picture.

20150409_135951-1.jpg
 
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#7
ok the idle jet passage is good.
now spray something into the air intake hole that leads to the idle air screw.
make sure the spray can be seen coming out the other side.
yes, that passage is clear too. i've taken macro images of every passage/nook/cranny on the carb that matters, they're all clear/clean.


while you're gathering the next suggestion, here are some pictures....
for instance, here's the float needle, choke plunger, air screw, and idle screw:








i was a little worried about the air screw, as it's not exactly a good fit down where it should be a tapered seat. the spring pretty much holds it aligned, but i don't have a 'good' or 'bad' carb to compare it to.

the plunger on the choke was also a concern, but i punched a dot (hole puncher) out of an innertube and dropped it down the choke hole to cover the fuel inlet, then inserted and tightened the choke assembly, and there was no change, so i guess it's not leaking there either.
 

jaguar

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#9
check for spark strength.
also you can check the stator coil. if it's partially shorted then its voltage output will be weak. disconnect the CDI and put an analog voltmeter on the two wires coming from the stator coil. cranking the engine with the spark plug out should give at least 40 volts.
 
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#10
OK, I'll try that when i get home. the Transmission level has been the same for a week now.

when i checked for spark earlier today it was fat and blue... but timing, i don't know how to check. i marked the stator assembly location before i pulled I off with a paint pen, but haven't put a timing light on it to verify. is that possible?
 
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#12
I'm talking about a big loss in spark strength or a big timing change, more than what the adjustable stator plate allows.
How did you check the crank seals?

i pressurized them with a bicycle pump and the best intake/exhaust plugs i could rig up... the plugs lost pressure, but the seals did not bubble soapy water, even at 15psi.
 
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#13
i did a little more reading last night, and some people have said that symptoms similar to mine indicate worn/broken reeds. this morning i pulled the reed box, and found the reeds are not sitting flush, the reed box is chipped in the corner and the reed backers (sorry, i don't know the right terminology) are not sitting flush either.

here you can see the chipped edge shining through the reed:


and the gaps, that don't look that bad in the pictures, but together the upper and lower reed+reedbacker are around .040" or a little more. I'm assuming this definitely won't help the jetting process:



^^^ the chipped corner is visible there too.


here it's more exposed:


and more of the overall condition:




to me, there don't look terrible, but definitely not tight and right.

opinions ? (i kicked the bike through with the volt meter, it showed 44volts if i remember correctly. the spark is fat and blue.
 

jaguar

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#14
fill in the chipped out part with JBWeld and let it sit 24 hours and then file it flat.
I don´t know if this will work but with carbon fiber reeds you can hold them about 10 inches over a flame (just hot enough that you can´t keep your fingers there long) and bend them in the direcxtion they need to go to seal better and they will hold that new curve. Or you can try reversing the reeds so the outward curve is now the inward curve (which you can´t do with carbon fiber since the outer side is not smooth).
 
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#15
fill in the chipped out part with JBWeld and let it sit 24 hours and then file it flat.
I don´t know if this will work but with carbon fiber reeds you can hold them about 10 inches over a flame (just hot enough that you can´t keep your fingers there long) and bend them in the direcxtion they need to go to seal better and they will hold that new curve. Or you can try reversing the reeds so the outward curve is now the inward curve (which you can´t do with carbon fiber since the outer side is not smooth).

thanks ! (a million)

do you think those tiny gaps are enough to cause this super weird jetting condition on their own ?

if you do, are you surprised that i didn't find more references online to 'bad reed symptoms', or is it just kind of rare / rarely known ?

really, thanks again. this is a ton of help.
 
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