Motorcycle Repair: will not return to idle, k n filters, fuel mix

Question
Hi Gary.  I have an '89 ZX1000. (A) Bike has pipe and K&N filters and I think previous owner overjetted as I was practicing parking lot turns and bike stalled. Plugs were pretty black and smells rich. Is there a way to check rec sizes?   

(B) Also, bike sat 2 years so removed carbs to clean bowls.  They didn't look too bad but now a few problems; 1) choke will not stay on, I have to hold while warming.  Is there a way to increase the friction or some other adjustment ?  (2) Engine will not reliably return to idle.  If I upshift at 5,000 and pull clutch in slowly comes down from 4,000 over 5-7 seconds.  Twisting grip everything moves fine and rear brake alone will haul bike right down.  My guess is that one carb is remaining open and that one cylinder can keep the engine at that speed. All of the slides seem to operate equally freely and don't seem dirty. These are Kleins.  I have not separated the top covers yet as whoever did it last stripped half of the heads from the screws. Haven't owned or ridden this bike much but seems like it should be a little smoother.

Any suggestions would be most welcomed.  Thank-you !!

Answer
I have some suggestions as you may be right and have multiple problems. The jetting could be to rich.Check this out first it could be a CA,CN,US model the will assist in jetting. Stock main jet could be 125,128,135,138 and the slow jets could be 30,32,35.Also the fuel mix could be screwed in to lean causing a not to slow down. Or the throttle cable could be routed wrong or too tight not letting throttle plates return quickly.The choke has a sliding bracket to pull all four of the choke pistons unless all have lost their detent lock something may not be working correctly. And yes one carb could have a shaft sticking or not in the correct position to the ajoining carb that also turns the shaft and has a syncronizing adjuster.Also make sure the slides are in correctly in the top of the carb as 1 slide may be higher than the others. All I can do is give you some trouble spots to look at without more info.