idle speed problem

When cold I need to use choke to start, I know this is very common, but after a few seconds from starting and anytime the bike is warm the choke will cause the the engine to cut out. Once the bike is running for a few minute I can get it to idle at about 1100 but as it warms up more I need to keep it up at 1500 or above or it will begin to cut out. This again changes after it is rode. It will be fine until I pull up to a stop and then the idle will drop back down around 1000 and want to stall. A couple of quick shots of gas will get it back up to around 1500 and it seems to stay there untill the next stop. Today I took it out for a short drive, when I got back it again wanted to drop down and die so I turned the idle adjuster up a slight amount and it returned to around 1500. Without turning it off I got back on for a once around the neighborhood and as soon as I revved the engine up a bit the idle jumped up to 3000 and stayed there until I got back home and turned the idle adjuster back down. I didn't adjust it much either time, at most a quarter of a turn.

This is an 81 KZ750 Ltd, all stock. I'm certain carbs are clean and so far have not found any vacuum leaks using carb cleaner around the boots. Just finished repairing the timing advancer which was stuck at mid point. Good spark and compression on all cylinders.

Anyone have any thoughts?

try spraying around the bodies of the carbs them selves right around the throttle blades you may have some air leakage around the throttle shafts just like on a rochester carb on a chevy also when you put the carbs back together what did you set the fuel screws at.

hmmm... good idea, will try that tomorrow. I set the fuel mixture screws at 2 turns out. This is what the clymer manual suggested. I did not get the carbs synched yet, just bench synched, as I'm still waiting for my vacuum gauges to arrive.

OK, I know this is a completely stupid question but I'm having a brain fart right now and my bike and manuals aren't nearby.

is the choke on when the lever is up or down on this model?

nevermind, it's on when up.... i must be getting old to forget that.

I finally got the carbs synched tonight, they were'nt far off. I had to adjust the air/fuel mixture screws to a full 3 turns out. It now idles nice around 1000-1100 rpms. I haven't taken it out for a test drive, had a few beers while I was workin on her, but let it warm up really well in the garage and it seemed pretty stable. I still may have an air leak somewhere as the idle hung up around 4000 when I cranked it open. It only happened once and I couldn't get it to happen again. I can't for the life of me find a leak anywhere. I sprayed carb cleaner around the boots and allover the carbs and did not get any changes in rpms.

So I am nowhere closer to getting this fixed. Once the engine is warmed it will only idle above 2000, any lower and it just runs for a minute and then dies. If I give it a good pull on the throttle the idle will hang up at 4000 until I back off the idle adjuster at which point it drops sharply and dies. I rechecked the carbs and cleaned them, tried the fuel mixture screws in every position from 1 turn out to a full 4 turns out, doesn't seem to make any difference. Checked again for air leaks and did not find any.

After going through all the manuals again I noticed something odd. Both manuals that I have, Clymer and Kawasaki, show the air suction system as feeding off the airbox and going to a vacuum switch. I don't have this on mine. Where this system links into the airbox actually has a line going to one of the vacuum lines on the carb. Could this be where my issues are coming from?

Do your carbs have the fuel pump? I have seen a bad pump diaphragm do strange things with idles and throttle blips.

Am thinking all carb vacuum nipples should be capped except the one with tube to petcock which furnishes vacuum to petcock.

And would assure vacuum tube from carb to petcock is not leaking (no cracks and snugly connected at both ends).

The floatbowl vent nipples should not be capped.

Good Luck!