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I recently purchased a 1989 and a 1990 KDX200. The 89 is in the process of a rebuild. The 90 ran good with the carb it came with but I had rebuilt the other carb so I installed it. The bike now runs like crap. I have the same jet sizes that it originally had. a 45 pilot and 150 main. clip is in the middle position. The bike loads up like crazy and the plug is wet. Its like it running really rich especially at the bottom end. Wide open is good. I thought maybe the float height was wrong. I checked that and it was good. I cleaned the carb with carb cleaner and blew all the passages. I checked the choke plunger and that seems good. I'm running out of things to check that I know of. Any thoughts????

Generally, it is not as clean as it needs to be. DO NOT soak it in Berryman's or similar. It will damage a hidden o-ring which will cause a rich condition.

Any chance a previous owner already did that?

Look up " jet block gasket "

I would put my money on the jet block gasket. Also, set your float height to 18mm.

I put in a carb kit which included the jet block gasket. I also raised the float height as suggested. I went for a ride today and its no better. I also see spooge at silencer, rear fender, etc..... When I rebuilt the carb it didnt look that bad either. Just did it as a precaution.

That would have been handy to put in the first post. :-)

If it really is clean and no passages blocked, then check the slide and body. Swap parts around to help out.

The carb is damaged or not clean, unless the crank seal started leaking around the same time.

Which plug are you using?

What gasoline and oil and ratio?

I am running premium pump gas. oil ratio is 32:1 and I use Shell advance synthetic oil.
Tomorrow I will swap carbs and see if its better.

OK, normal sounding oil and gas

Why don't you put the other carburetor back on it as it was before, and make sure that the problem was with the rebuilt carb? It might have a different slide cutaway in it, or different needle or different brand of jets that say they are the same size but are not actually the same. Aftermarket jets do have some variances in them as far as size and tolerances relating to flow.

So, finally the 1990 is running much better. I thought I had replaced the jet block gasket/o-ring but I had not. When I saw that, I ordered one on ebay and installed it. Much, much better, however, I'm still getting some spooge. Is spooge a condition or running too rich a mixture or too much oil? As I mentioned, I'm running 32:1

If the transmission/clutch oil is not blowing past a leaking right side crankcase seal, then you may have some oil built up in the pipe and/or silencer. If all is well, start with the pilot and work your way up from there.