OK, pulled the carb off again and inspected everything carefully. Nothing out of order. Re-removed the pilot and main jet and soaked them overnight in carb cleaner (again) and blew them out with compressed air. I adjusted the floats, adding 2mm to the height (from carb body to top of floats when just touching the needle valve - approx. 16mm now). Double checked the diaphragm and it all looks good, with top getting metal-to-metal contact and slide passing the finger test.

Also cleaned the little screen/filter at the fuel inlet.

Put the carb back on and remembered this post about the spark plug. I didn't think a bike with 600kms. could possibly need a new plug but it's black with soot. Does that give you any ideas?

 

Black with soot !
Nothing "right" about that at all..
Let's hope it isn't burning oil...

Replace it - go with the equivalent iridium plug for a performance boost..

 

The carb had been monkeyed with by either the previous owner or a dealer he took it to. I wonder if it's possible they put a bigger pilot jet in and opened the A/F screw too much. I looked on the pilot jet to see if it said what size it is but I couldn't see anything. Doesn't the black plug indicate too rich jetting?

I'll replace the plug but I'll hold off buying the more expensive iridium until I find out why the first one fouled.

At this point I don't know what to do. Frustrating. I could put a new pilot jet in, (local Kawasaki dealer wants $30! for one), and/or turn in the A/F screw a bit more. I'll re-check all the vents and hose routings. I mentioned previously that the right side clear vent hose was burned off by the exhaust. I went to 3 places and no one had clear, so I bought black rubber. Is that OK, or does it have to be clear?

 

From Dr.Google:

Carbon fouling is an indication of a rich air-fuel mixture, weak ignition, or improper heat range (too cold). Carbon deposits are conductive and can create a path for spark plug misfire.

And:

Black, dry soot on the electrodes and insulator tip indicates a carbon-fouled plug. This can be caused by a dirty air filter, excessive driving at low speeds, too rich of a fuel/air mixture or idling your vehicle for too long.

 

When it comes to plug reading, only read articles that refer to plug reading when burning E10. If the previous owner, somehow, only burned 100% gasoline (very unlikely), then what you've just posted is true. Otherwise it is not.

Stop with the armchair analysis crap (Blackened plugs, Fuel screw settings, pilot jet sizing, etc) , you say you have achieved a good running bike (while on the kickstand) - this disproves all that crap..

FYI:
1. Soaking the pilot jet and emulsion tube does NOT clean them if they are clogged. The pin holes in each require much manual labor to clear and replacing a badly clogged pilot jet is sometimes necessary due to the pinhole down its' center being unclearable.
2. If you do not know what the emulsion tube is, you cannot reassemble the carb until you have removed it and completely cleaned its' pinholes.
3. DO NOT forget to verify that every single transfer port is clear and functional (sometimes they are called the transition ports) - they are a part of the pilot fueling system and provide the simulated "accelerator pump shot" of fuel to keep the engine from bogging anytime the throttle is snapped open ! This is a part of the pilot fueling system that is overlooked/unknown by "shade tree" mechanics and obviously cause huge problems when nonfunctional..

Get the above carb parts properly unclogged, the transfer ports verified functional, all the hoses replaced and routed correctly - black, clear, or polka dotted.. This will not be easy to do if the previous owner had the hoses "hooked up" all wrong.
Then get the new plug in and fire it up..

 

I've cleaned the A/F screw and it's port/passageway and the pilot jet and the main jet and the emulsion tube and every port/passageway I could find. I used carb cleaner, both spraying and soaking overnight, and a strand of copper wire to clean everything. I can see daylight through every tiny hole. I think it's clean. I put the carb back on the bike yesterday but did not put the tank, etc. back on. So... I'll pull the carb again and check everything, for the 3rd time.

I can't get a new pilot jet in reasonable time, (or at reasonable cost), so I'm trying to use the one I have. If there was dealer close by that had one in stock, I'd just buy a new one. I was hoping to ride this thing a bit before snowfall. Maybe I should just order the pilot jet and write off this season but we make decisions based on multiple factors and expediency was one of them in this case. That's fast going south on me.

This is also why I'm "playing arm chair quarter back". In trying to get a new pilot jet, I was told that the size # should be stamped on the jet. I cannot see a number anywhere on my pilot jet. I then speculated (dangerous, I know) that someone may have swapped it out, possibly with a non-Keihin one that doesn't have the # stamped on it. If it's too big, all the cleaning in the world ain't gonna fix this thing.

 

I don't know how to get your head right - maybe start sniffing glue.. I have no idea what you think a pilot jet has the power to do, but whatever it is, you are wrong. After your bike is running correctly, perhaps you should re-read my CVK posts and research the CVK pilot system for your peace-of-mind..

All that is important is that the carb components and circuits are declogged and clean, the carb is reassembled correctly, and the float level is correct. As I said much earlier, you do this over and over until it is done correctly. If you have achieved this, then you are done with the carb for now.

If the fuel filter is clear, and the hoses are correct, then you are ready to put in a new spark plug and fire the bike up.

 

And I told you much earlier that sniffing glue is a bad idea for me. Can't afford the brain cells, don't have enough as it is.

From your last post: ...replacing a badly clogged pilot jet is sometimes necessary. That's all I was trying to respond to. I was saying I'd just replace it if I could get one reasonably quickly. But if it makes you feel better, I'm not obsessed with it... just trying to "do this over and over until it is done correctly". As time permits. Hopefully put in some time this week and hopefully get 'r running on the weekend.

Thanks again for your input.

 

As far as I can tell, you have a functioning pilot jet, a well cleaned carb, a clean fuel filter, and a new plug.

So, as far as I can tell, you need to fire up the bike, get it to operating temp, set the idle speed to 1250 - 1300 rpm, and ride it..

 

Well this is either going to make you laugh or **** you off, but here goes:

I was almost certain I had that carb clean and it wasn't sitting well that when I put it back together the bike still had the same symptoms. Something should have changed. So before I put the carb back on I went through the exploded carb diagram in the service manual and went through the carb one more time.

AND... the Needle Jet is... MISSING!!. It looks like this, (this isn't the exact one for the KLX250 but it's similar):



With the carb upright, it's on top of the main jet holder/emulsion tube and the needle fits into it. Without it, I would think way too much gas would flow through, causing the bike to fall flat on its face and fouling the spark plug. My only question is how did it run OK on the side stand but not under load?

When I took it apart, I had a clean towel on the bench and opened it up carefully. I'm positive it did not fall out and disappear. Since it was exhibiting the same symptoms when I got it, I'm going to blame whoever opened it up before I got the bike.

So, if this is the answer, I've wasted your time and I apologize. I don't do this on a regular basis and just didn't know it was supposed to be there.

I'll post the results when I get the part installed and try it out.

Just under $50 CDN and won't be in until next week. At least I think I have the answer.