Jetting help.

A reference for the PWK carbs...
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swingset
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Jetting help.

Post by swingset »

I bought a very nice '98 KDX 200 off a guy I know. I haven't owned a 2-smoke since I was a kid, been on 4-strokes for a while so I'm kind of a babe in the woods with this bike but trying to learn.

He said it was jetted very well, ran great and my test ride it rode well...seemed to be awesome. But, on my first trip the trails I kept stalling on hills or after being on the throttle/in gear and clutching to a stop. Dead every time. If I turned in the idle screw enough to keep me running on clutch-ins, it reved to the moon cold or in neutral. And, the idle seemed erratic all day.

That sounded to me like a fuel starvation issue, so I tore into it tonight. Fresh fuel/oil mix (synthetic 40:1, 93 octane), fresh plug, fresh air filter, pulled the tank and cleaned the petcock. Inspected the reeds (perfect), pulled the carb and checked everything out as best I could (cleaned with carb cleaner, compressed air, pulled PJ and MJ, needle and float. The only thing I didn't check was the float level, not 100% sure on this carb how to do that...the manual was kind of confusing.

The jetting seems odd to me, but here's what's in it... stock motor (no mods), good compression (top end is pretty fresh, too). FMF Gnarly pipe, FMF power core 2, airbox drilled with 1/2" holes and snorkel removed. Elevation is 1,000 ft.
PIlot Jet: 48
Main Jet: 160
Needle: Clip in 4th slot from the bottom.

Air screw was out at about 1 3/4 turns.

Does that seem about right?

I tried following the jetting sticky as best I could, but even after re-assembly it's just kind of all over the place. The bike behaves very differently at idle once you're on it and coast...and no matter how well I thought I had it sitting in the driveway, once I rode it with some throttle and coasted clutch-in, it died.

If the jetting seems ballpark, anything I might look for? How about the float...is there a good "how to" on checking the level?
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SS109
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Jetting help.

Post by SS109 »

To set the float turn the carb upside down and measure from the float bowl flange up to the highest point on the black plastic of the float and bend tab to get the desired measurement (16mm IIRC). Get that set then we can go from there.
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swingset
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Jetting help.

Post by swingset »

SS109 wrote:To set the float turn the carb upside down and measure from the float bowl flange up to the highest point on the black plastic of the float and bend tab to get the desired measurement (16mm IIRC). Get that set then we can go from there.
Cool, figured it was something like that. Will check back.
swingset
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Jetting help.

Post by swingset »

Well, float needle looks perfect, the float was at just under 17mm, well within spec.

Scrutinized the needle and slide a bit more too, 1174K (stock) and it looks good. The slide is stamped #5, which IIRC is stock as well. There are a couple very tiny scratches right around the step/shoulder on the needle, but I can't even feel them to the touch or running a fingernail over them and I don't think that area is very crucial but I'll get some fine emery cloth and buff them out just in case.

Other than that, I'm stumped.

I might try a different gas and mixture, as it's the one unknown. Previous owner told me he was pretty sure it was 94 octane and a 32:1 mix, I only have access to a 90 octane non-ethanol gas but I would be very surprised if that alone was enough to cause the weird idling.
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Jetting help.

Post by SS109 »

Old crappy gas can cause all sorts of weirdness. Definitely get that out of your carb and tank and refill with fresh premix using a quality 2T motorcycle oil. I wouldn't touch that needle with anything! If you can't feel a scratch with your fingernail then don't worry about. Even a super fine emery cloth will change the profile of the needle. Remember that needles are speced down to a 10,000th of an inch!
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Jetting help.

Post by rbates9 »

+1 If the gas is even close to old I would toss it and start over.
swingset
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Jetting help.

Post by swingset »

rbates9 wrote:+1 If the gas is even close to old I would toss it and start over.
It's fresh gas, just a different octane than the OP said he ran in his mixture.

I'll still replace it with what he claimed he jetted for, just to eliminate that as a possibility.
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Julien D
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Post by Julien D »

What was it he was running?
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Jetting help.

Post by swingset »

Julien D wrote:What was it he was running?
He said 94 octane and a 32:1 mixture.

I wouldn't be shocked to learn that I got bad gas, but I also wouldn't expect just the octane rating alone would count for a poor running condition all things being equal. Will report back with the fresh gas....if that doesn't fix on to the next thing.
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Post by Julien D »

ethanol free 90 should be fine.
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swingset
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Re: Jetting help.

Post by swingset »

Found something interesting, might be my problem....the airbox boot had some oil in it when I was cleaning it out. I used No-Toil and my trail ride was pretty warm...wondering if it didn't break down and get into the intake bell and clog a passage? I've heard of No-Toil doing this before, but never experienced it...but it's plausible.

Anyway, ordered some new jets (always feel better using a new, rather than cleaned pilot after a carb cleaning plus I got a few leaner jets just in case). When those come in I'll get the fresh gas in there, start from scratch and see where my problem lays.
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Jetting help.

Post by swingset »

UPDATE! Success!

I wish I could say which thing conclusively fixed my problem, but I think it was probably a recipe things that were wrong. I cleaned the carb thoroughly, bought new jets (same size) and needle, and some other jets for fine tuning. I got fresh 94octane, 32:1 synthetic, clean air filter, fresh plug, and re-installed.

Fired up, and the issue seems to be gone no stall. After some riding, as I suspected the bike is too rich across the spectrum...bogs a tad, sluggish, lots of smoke and splooge....but the idle was smooth and constant, no dying on coast or clutch-in.

I switch from a 48/160 to a 45/158, same needle position (2nd clip) and tried that this morning...much better. Snappier response, pulls better, seems good all over. Air screw was 1 3/4 out, and idle is still good. If I had to guess, between the gas, the too-rich pilot, it just was just drowning at idle.

I still get a little splooge, but I've heard the KDX when properly jetted pukes a little and this is not a bad thing.
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Re: Jetting help.

Post by CoronasAndChips »

Awesome! glad to hear another success story.
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