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1974 Z1A, clutch handle almost impossible to pull. cable lubed, clutch release mech.,cleaned and greased. nice fluent motion all the way up to clutch pusher. pulled old steel and fiber plates out. with great difficulty, wedged against right side of clutch housing. installed new fiber plates, cleaned steel plates. difficulty installing fiber plates same side of housing. still extremely hard clutch pull. new stock springs also. could the housing be warped?

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Dave

Check the push rod, if bent it could bind. Try with only 3 springs to see if it’s too much spring pressure. Don’t drive it just test the function of the clutch. Check that the pusher isn’t sticking in its bore. With the steels and fibers out make sure the spring plate slides smoothly on the post the bolts thread into. 95% of the time is a bad cable.

The plastic worm gear gets worn with time and binds to the point of breaking cables. I installed a later model actuator with the ball bearings and it's like night and day. Before that I welded an extension on the arm that made it easier but it still was stiff. In the past I bought sprocket covers no matter how they looked just for the worm drive. Won't go there again after 40+ years with a stiff clutch and broken cables. 
Steve

You're right Steve, the ball bearing actuator was the solution on mine too.   

I use an Easy Clutch on all of my Z1 bikes. 
www.z1enterprises.com/easy-clutch-kit-z1...J_rpoqEaAsuyEALw_wcB

A bit spendy but worth it in my opinion. 
So I would replace the cable and make sure it's routed correctly and install the easy clutch. It sounds like you replaced the springs with stock springs so thats good. No need for heavy duty springs on a stock bike, The clutch housing is a pretty beefy unit so I doubt that it could be warped/bent.

that's exactly what I was thinking, the clutch housing is steel, clutch hub aluminum. removing old plates and installing new ones, having the same resistance on the right side of the housing. almost like it's out of round. I wouldn't think the plates should be binding only in that area. I have replaced clutches on Hondas in the past and never had to fight to get plates out or install. thanks for your help. 

The steels and fibers have no affect on pressure felt at the lever. When you pull the lever your over coming spring pressure on the spring plate to push it away from the stack, thus allowing them to slip on each other. The only way the disc would come into play is if they were frozen up and sticking to the spring plate. So your looking for resistance in the clutch cable to inner sheath, the rotation of the clutch release, the push rod within the bore of the trans shaft, the movement of the pusher within its bore, the spring plate friction on the post and ultimately the clutch springs themselves. 

If you have a clutch release the has the plastic ramp this  Clutch Release  is a cheap upgrade. 

 

Is the lifter mechanism excessively worn ? it may move freely when removed but if badly worn, when under pressure it can "cant over" to one side causing it to bind

I agree with all that has been suggested by others to this point. But if the push rod has been removed and the pressure plate and springs pulled as your pic shows and there is binding between the outer and inner clutch hubs I would think the outer hub should be pulled and the bushing and bearing on the outer hub needs to be looked at. I just can not get my head around a binding between the outer and inner hub when there is no pressure on it. It could also be the bearings on either end of the trans shaft the push rod runs through.

Not saying this is what is happening to you, but again I (as a old man) can not see how the binding will happen with out any pressure on them.. But then again what do I know?

www.kawasaki.com/en-us/owner-center/parts/143420/1974/Z1-A900

Double check that the pressure plate is fitted right  in the groves.I know it can be done wrong on other bikes.

If that hub is bent the only thing you can do is check with a dial indicator positioned on the sides while still in the engine..
www.zoro.com/starrett-dial-test-indicato...AvD_BwE&gclsrc=aw.ds
rotate and check each arm, do the same on the inner hub.. you would need to split the cases to check the condition of that clutch hub bearing. You can remove the nut and pull the inner hub off and see if you have any play at the out hub.