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Hi guys. New KDX owner here...just picked up my first 2 stroke, a 2001 KDX200.
Bike has snorkel delete, 42PJ, 155MJ, 1174 needle in 2nd clip. It also had a bent pipe that was sticking out few mm (showing the outer seal ring), so after buying the bike we test rode it and figured that we could fix the jetting a little since it's a bit spoogy and with the pipe not seated all the way it could be sucking some air in...so I've set out to clean up the bike.

I've added Boyesen 607 power reeds and got a gnarly woods pipe. Bought a JD kit, and now trying to install it and jet properly. I'm at 5000 feet and my MX track is at 5000 but woods we will ride in are 6-9k elevation. At least humidity is low and fairly constant (Colorado).

So this is what the trouble is. I can't seem to get even the idle circuit dialed in properly.
1. What's a good idle screw setting (not air screw, idle). For me, the only way I can get the bike to idle is when idle screw is when it's within 2 turns of fully seated. At this point the slide is probably up about 2mm, and I'm suspecting that bike idles not on pilot jet but also picking up a needle. I'm suspecting that b/c only changing from 1174 to JD red needle causes bike to idle like crap (idles fine with 1174 with idle screw out 2 turns, idles like crap with JD needle).
I did a bit of experimentation with the carb off today, and at idle screw 9 turns out the slide is fully closed, and ready to open.

2. Using previous owner settings (42, 155, 1174 in 2nd clip), testing locally at the track bike revs fine through the entire range, however it feels flat on main jet...I open the throttle and roll on through entire range, and feel the power increase until last 1/4 throttle where it just stays flat. Does that mean MJ is rich?

3. Can plug chop test be done in 2nd or 3rd gear? I don't think I can find a long enough road here to do a 5th gear WOT test.

Thank you for responses, I swore I'd not buy another carb'ed bike...and here I am :) Ready to go buy a Lectron now...

1. I would suspect that your pilot jet is a little too rich necessitating having the slide partially open to idle. Ideally you would set your idle with the slide closed at your lowest altitude. Where is your air screw setting? That will give you starting point for the pilot.
2. Main is probably also a little rich, but work it after you get idle setup.
3. You can do it but it's not optimal as you want to put a good load on the motor. If you have to do one short in the gears try and run somewhere on an uphill incline to help load the motor.

It's difficult to dial in air screw when bike doesn't idle. I have to keep revving it constantly. I was running 42PJ earlier today, air 1.5t out, and bike wouldn't idle at all unless idle screw was in pretty far. (fully in to 2 turns out, so running with cracked open slide) Is it normal for bike to take 5-10s to respond to air screw changes?

I'm going to install 40PJ and try again, with idle turned out pretty far to close the slide, and hope that it works. Not worried about MJ yet...pilot first

pull the pipe and inspect the cylinder/piston.

it's really hard to jet a work out bike.

I did that when I bought the bike. Piston looked good and not worn out.

Worked on the bike a bit. Put in a new PJ40, verified that both idle passages (after slide and before slide) are open.
Floats are set at 17.5-18mm due to bike peeing.
I let the bike warm up a bit, ran it up and down the block, for about 5 minutes total.
Idle screw was set to about 4 turns out, air screw at 1.5t. Bike initially had a hard time idling, always shutting down, until I scwered idle in to about 4t out. Bike idled OK, I was able to get a good idle going, at 4.5t idle dropped, so I adjusted it up a bit and played with air screw.
RPMs would pick up at 1t out and max out about 1.5t out. So...just as I thought I had it dialed in...bike died. Kicked it again, and it wouldn't idle anymore. I had to screw the idle back in all the way to get it to run, and basically have to restart adjustments again.
It's this inconsistency that's annoying...Any ideas why it would be like this? Air leak somewhere?

Yeah, Keihin actually recommends giving it 30 seconds or so for air screw adjustments, though usually you know around 10-15. I know the frustration, I am going through it right now with a 95 RMX250 that just doesn't want to idle. Did a leakdown test and its right on the edge so I'm going to replace crank seals and reeds and see where that gets me. I am assuming you cleaned the carb, but could be a jet block gasket, pretty common issue on the PWK carbs. I would do a leak down check, and when you have it running shoot some carb cleaner around the boots to check for air leaks there.

I've read a post recently on PWKs and a guy removed the jet block and the gasket seems to be protecting only air passages, not fuel...the gasket isnt even included in rebuild kits. I guess if I'm chasing random issues...maybe? But it's pretty hard to find one, google certainly doesn't have much.

I did install boyesen 607 power reeds and the instructions read "Power reeds tend to make the bike run rich, drop 1-3 sizes on MJ". Holy crap, that's a lot. I wonder if I have to go even smaller on PJ, right now with 40PJ the air screw is 1.5t out. But then again, I'm having weird issues. Tomorrow I'll give it a shot of carb cleaner near the boot and see if there's a leak.

If the jet block gasket is leaking, it will suck unmetered fuel out of the bowl causing you to run rich. The gasket can be found at Jets-R-Us. http://jetsrus.com/individual_parts/021_532_su.html

Thanks, that's a good point. I'll order one and see if that helps.

For roughly ten bucks, it is one cheap thing to eliminate for certain.

Had a chance to work on bike.
1. Discovered the likely cause of "bike idles then just dies"...MJ was loose in the bowl. Must not have tightened it and it shook loose. Whoops.
2. No air leak around the boots. Sprayed a lot of carb cleaner, no change in rpms.
3. Choke kills the bike, which means it's not lean, therefore it's rich.

Boyesen 607 power reed instructions say they make the bike run rich and to drop MJ by 1-3 sizes...I wonder if they enriched the whole circuit so I have to drop PJ too (it was 42 from previous owner, and ran well, adn now doesn't). So I'll go to PJ40 and work from there.

Whoops indeed.

Have you ran it since you fixed your error?

Yeah I put MJ back in and attempted to run it again so I could check for air leaks.
The main problem is...bike won't idle unless idle screw is ALL the way in, or maybe up to 2 turns out and its inconsistent. I could set idle and be fiddling with air screw, bike would die and on next start it would idle completely differently. I can't quite understand what's going on.

I am not seeing where you cleaned the carburetor, or how you did that.

First thing I did when I bought the bike was get a card rebuild kit. All jets are new. I've sprayed out every passage I can, including removing the choke. The pilot circuit is clean, at least I've sprayed it out and both passages are spraying (one that comes out in the slide and one that's past the slide, although this one is a lot smaller and produces smaller spray). So the only thing I haven't replaced is the jet block O ring gasket, that's in the mail now.

Put a 40PJ in and it seems to be running better. I was able to take the idle screw out a bit and find where the slide closes and keep the bike idling...so the actual idle point. Haven't played with air screw yet...I went through the range and I *think* 2t is where the idle picks up...not sure.
Also, with idle screw in pretty far, bike will rev high for 10-15s then low...basically like a hanging idle? So...is the needle too lean?
As soon as I crack the throttle, though, the bike hesitates, sputters a bit, revs (there's no power, took it for a ride and it's non-existent) and then as the RPMs come down, dies, won't stay idling. I basically have to keep revving the bike a bit, turn idle way up, then turn it back out to where it should be.

Is that b/c the next circuit (needle) isn't dialed in and running rich/lean, so when I rev that rich/lean gas gets into system, but by the time I've closed throttle hasn't been consumed fully yet so bike tries to idle rich/lean and can't, so dies? Or is there something more sinister at play here?

It appears it was the jet block gasket. Bike now idles after revving. Onto more jetting.
The gasket was probably original, plasticized and very flat, so it's possible there was some cross-leakage between fuel channels in it.

Thanks for the follow up. There have been a few people mention it improved after replacing the gasket.