Where is the slave cylinder to bleed the clutch kawasaki vulcan 1500 1992

Try changing the hydraulic clutch fluid as it sounds like its failing as it gets warm

If the lever was fine as you bled it then the problem lies elsewhere, either the slave cylinder is stuck or the push rod mechanism in the clutch itself is assembled wrong.

undo the bleed nipple slightly on the slave cylinder , remove cover on clutch lever and make sure to keep it topped up as you bleed ! pull lever and hold as you nip up the nipple then release lever ! do this several times , be careful not to get fluid on paint work as it will melt it ! once done top up fluid and fit cover and try !

The clutch bleeder is behind the left engine cover, you will have to remove the left exhaust from the head and also the left front foot peg in order to get it off should be about 5 bolts holding engine cover on dont worry its just a cover no oil leakage from that side, then it will be down just above the frame, it will have clutch hose going to it.. to Bleed it remove cap on leftside handle bar make sure fluid level is 3/4 fulll hold clutch lever in then open valve, let air out then close valve release clutch lever, should fix if not repeat bleeding until you have good pressure on clutch lever, dont let fluild get to low . once pressure is good refill and put cap back on. put bike back togather and RIDE good luck

The best success I have bleeding my clutch is to do it in this order.
1- fill reservoir with dot 4
2-loosen bleed screw on slave cylinder and let gravity bleed
3-never let reservoir run out while gravity bleeding
4- when you see steady dripping fron bleeder screw, tighten screw.
5-top off reservoir with fluid and install top back on reservoir
6-loosen bleeder and squeeze clutch all the way in one time and hold it.
7-tighten bleeder before releasing clutch
8-repeat this step one more time
9-remove reservoir top and refill the cylnder
10-put top back on reservoir
11-pump clutch handle 5 times and hold in
12-open bleeder screw
13- repeat this step 3 times
14- you should have a good clutch
15-check fluid in reseervoir one more time to make sure it is still full

It is under the left engin cover. You have to remove the shifter and the footpeg or floorboard too. Then remove the 4 or 5 allen bolts and the cover will come right off. No oil or anything will leak when this cover is removed. You will see the clutch slave cylinder behind this cover. I found the best way to bleed the clutch is to fill the master and open the slave and let it drip for a while (gravity bleed) Do not let the cylinder at top run low while you are doing this. After a 10 minutes or so, tighten slave then refill cylinder and do the old pump and drain bleed a few times. I found that it works better with the cover installed on the cylinder when pumping to bleed clutch.

if your oil is too thick , your clutch will sleep and go away .
if the clutch is old , you obviously will have the same problem .
please explain your problem when you ride

if the bleeding temporarily helps you may have a bad master or slave cylinder, check the system really good for leaks. also check that your hose isnt pinched or cracked.