a little jetting help please

A reference for the PWK carbs...
ohgood
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a little jetting help please

Post by ohgood »

97 kdx220
fresh top end
boyeseon reeds
no air box top
clean filter
gnarly chamber with fmf Rev
fresh gas
600ft to 1200 elevation
50f to 90f


yesterday i ran it with
35 idler
135 main
needle in the middle (third from top)
screw at 1 3/4 from bottom
and it did well. starts easily, oodles low, and pulls well. anything just of idle, or steady lower throttle is hiccupy, but smooths out easily with throttle.

today i tried 38 138 same needle position, and couldn't complete a fuel run of less than 5 miles.... same screw setting, and it ran similarly, but lots of throttle made it bogd/die and would not restart for 10-15 minutes.

isn't 35 / 135 too lean ? would 38/138 make it flood/foul that easily?

i've tried several combinations from 35/135 to 40/142, with different needle positions and combinations, but it gets boggy and poorer the richer i go.



points? tips?
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Jaguar
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Re: a little jetting help please

Post by Jaguar »

don't think of the main jet as for anything other than wide open throttle running.
In your post you never mention how it ran at top rpm.
35 sounds like a good idle jet for you.
set the needle height for accelerating as you open the throttle up from 1/4 to 3/4 open.
double check that your float height is correct.
If you set it to be a bit rich at 600ft then it might not be too bad at 1200ft.
Performance CDI -- KDX motocross mods -- the SR KDX -- expansion chamber analysis---> http://www.dragonfly75.com/moto/
cornishwrecker220
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a little jetting help please

Post by cornishwrecker220 »

I personally would keep the air box lid on & just remove the snorkel, add 3 x1 inch uni filters to the top of the lid ,220s don't really benefit having the lid removed as they don't run like the 200s up top anyway .

Next I would install a 38 or 40 pilot jet & 145/148 main jet....needle in 2nd from top position & go from there....if running a 38 pilot & 145 main then install needle clip in mid position & try that , remember to tweek the air screw to 1.5 / 2 turns out.
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Re: a little jetting help please

Post by ohgood »

OK, thanks guys I'll try that today. the lid has been gone for a long time, so I'll have to buy another if that's best.

my mein concern was running too lean. if y'all aren't concerned, i won't be either.
cornishwrecker220
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a little jetting help please

Post by cornishwrecker220 »

Your current jetting is too lean, especially with the air box lid removed.
You can jet to suit with the lid removed but with the 220 it's very difficult to jet the motor clean , for it may run clean down low but lean on top or visa versa.....
At a base setting I would say that with your lid removed a 38 pilot & a 148/150 main jet with the needle in either the mid or 2nd from bottom setting would be a good starting point.
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a little jetting help please

Post by ohgood »

cornishwrecker220 wrote:Your current jetting is too lean, especially with the air box lid removed.
You can jet to suit with the lid removed but with the 220 it's very difficult to jet the motor clean , for it may run clean down low but lean on top or visa versa.....
At a base setting I would say that with your lid removed a 38 pilot & a 148/150 main jet with the needle in either the mid or 2nd from bottom setting would be a good starting point.

yesterday i ran 38 / 138 and it fouled a $9 BREIX plug in less than 4 miles.

the symptom is always the same, no matter what jets are in it:
starts up without choke in 50F cold starts
runs like **** at 1/8 to 1/4 throttle, but fine on acceleration

pulled the reed box yesterday, looked in cyilnder, cleaned carb. nothing to report.

the consistancy of the poor running has been the same through ALL the jetting changes.
cornishwrecker220
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a little jetting help please

Post by cornishwrecker220 »

Clearly there's an issue with too much fuel going in to foul plugs that quick...
It's possible that the "jet block" rubber gasket has given up allowing extra fuel to be drawn through ?
You can buy a new gasket & try that, or simply do a carb swap if you have a buddy who can lend you a carb?
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Re: a little jetting help please

Post by ohgood »

cornishwrecker220 wrote:Clearly there's an issue with too much fuel going in to foul plugs that quick...
It's possible that the "jet block" rubber gasket has given up allowing extra fuel to be drawn through ?
You can buy a new gasket & try that, or simply do a carb swap if you have a buddy who can lend you a carb?
yes, i have the new gasket installed.
yes, I've swapped carbs.
cornishwrecker220
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a little jetting help please

Post by cornishwrecker220 »

Ok well we are getting there slowly ....

Are your crank seals ok ?
Does the bike smoke ?
Gear oil level dropping ?
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a little jetting help please

Post by CAL-kawi »

Both 220's I've set up needed 38-40 / 140-145 with the clip in the 2nd position (from top). This is at similar elevation with similar profile pipe and boyesen reeds. I agree that something else may be going on, maybe too high a float level? Too cold a plug? Shouldn't hurt to try the leaner clip position though.
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Re: a little jetting help please

Post by ohgood »

cornishwrecker220 wrote:Ok well we are getting there slowly ....

Are your crank seals ok ?
Does the bike smoke ?
Gear oil level dropping ?
crank and bearings are new, level has been consistent for 5 hours of riding while testing jetting
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Re: a little jetting help please

Post by ohgood »

CAL-kawi wrote:Both 220's I've set up needed 38-40 / 140-145 with the clip in the 2nd position (from top). This is at similar elevation with similar profile pipe and boyesen reeds. I agree that something else may be going on, maybe too high a float level? Too cold a plug? Shouldn't hurt to try the leaner clip position though.
42/142 second from top, 1 1/2 - 2 turns, 17 mm float height, fouled two plugs (br8eix iridium) while riding yesterday.
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a little jetting help please

Post by CAL-kawi »

Going up to the 42 seems like a step in the wrong direction.
Some things to check, mine like the air filters squeezed out really well. I've also had carb needle valves go bad, or the valve seat gets some varnish and doesn't seal. Might be something simple that's just been overlooked?
cornishwrecker220
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a little jetting help please

Post by cornishwrecker220 »

Has the problem started AFTER you had the fresh top end?
If so maybe the kips was installed wrong or not timed up correctly?

What needle are you running in your carb...was the carb off a 220 or 200 ?
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a little jetting help please

Post by ohgood »

cornishwrecker220 wrote:Has the problem started AFTER you had the fresh top end?
If so maybe the kips was installed wrong or not timed up correctly?

What needle are you running in your carb...was the carb off a 220 or 200 ?

the problem (poor constant throttle, and/or 1/8-1/4 throttle response) was there prior to the top end, but only for one day. previously it ran very nicely at constant throttle, and the bottom end (1/8-1/4) was fantastic.

KIPS is working, i've verified that at several points throughout several rides now.

i ran i pretty hard yesterday, lots and lots of revving, lots and lots of single track, and did not foul a plug. i'm going to repack the silencer again, and see how long this plug will last.
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a little jetting help please

Post by cornishwrecker220 »

Fit a new spark plug cap on while you're at it....they don't last forever & sometimes get over looked.
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Re: a little jetting help please

Post by ohgood »

cornishwrecker220 wrote:Fit a new spark plug cap on while you're at it....they don't last forever & sometimes get over looked.
i have a new coil /wire/cap
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a little jetting help please

Post by cornishwrecker220 »

Sounds like you have spent quite a bit of money on the bike ....

I guess all that remains is the pick up coil or stator plate to check/test .....

If you haven't already done so ?
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a little jetting help please

Post by ohgood »

cornishwrecker220 wrote:Sounds like you have spent quite a bit of money on the bike ....

I guess all that remains is the pick up coil or stator plate to check/test .....

If you haven't already done so ?

i soldered in a new stator (ignition) coil a week or so ago. there was no change in the running condition of the bike afterwords, so i'll be keeping the old coil in my parts bin for future use, should it be needed.

i could just about split the cases in my sleep now... but the reassembly would mean opening my eyes, or burning my fingers really bad on the heat gun ;-)
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Re: a little jetting help please

Post by ohgood »

changed to Lucas …@ 40:1, and on the first street ride, fouled a plug in twenty minutes:

Image


the Lucas and 40:1 felt better, especially at the lower throttle openings.

apparently i still need more jetting work.

Monday i rode for three hours without issue, on one plug.
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