Engine slip - clutch, carb setting or vaccum leak?

Hey guys - I am having problems trying to diagnose my issues here. I have a 1981 kz650 CSR that just doesnt want to perform properly. When the bike tends to rev on the high end; typically over 6k the engine slips resulting in zero acceleration past that point. My first reaction to the problem was replacing the clutch discs and springs. This did not solve the problem. Can the carbs settings/jetting cause the same problem? Typically when I start the bike with full choke it will fire and then run away to redline - until I go half choke to keep the bike at a decent idle speed to warm up. After about 5 minutes at ~1500RPM from a cold start - when trying to ride the bike it will almost stall out until it is fully warmed up or whatever the case may be. Could it just be a vaccum leak leaning out the mixture? I know these bikes are notorious for not running with leak so I was hoping that someone else may have encountered this and have a solution

Any suggestions will help!

If the engine revs but the bike doesn't accelerate the clutch is slipping. Do you have the Kawasaki Service Manual? Did you adjust the clutch and cable using the instructions in the manual? What motor oil are you using? Ed

Thanks for the reply Ed,
I do have the service manual - but didnt really think about clutch cable adjustments after replacing the discs and springs.. I will have to try that tonight. Regarding the motor oil - I use a 4 stroke motorcycle oil; I can't remember the brand off the top of my head.

As long as the oil container is marked "JASO-MA" you should be fine. I believe most 4-stroke motorcycle oils have that designation. Ed.

I would check the petcock to make sure it's functioning properly. A defective diaphragm can be a source of a vacuum leak & sometimes you can't tell it's defective by looking at it.

Remove the vac line & cap off the vac ports, then start the bike in PRI. With the vac line removed, ON & RES function as the OFF setting. This bypasses the diaphragm assy & it's what i did to verify that it was defective.

Ignition system. When the bike is cold, start the engine then pat the exhaust pipes to see if they're heating up evenly. Don't get burned. It could be that one or more cylinders don't fire immediately. In my case it was poor spark plug wire connections --- unscrew the ribbed compression boots at the coils & untwist the spark plug boots. You could nip off the ends of the wires a tad to get fresh connections. Or go ahead & get new spark plug wire (7mm copper core, I think).

Ok guy i took my project bike out for the first time today, and guess what, I'm having this exact issue!!! Carbs are adjusted fine and no vac leaks that I can find. At I'm guessing ( no tach) 5k rpm I believe my clutch is slipping as the bike does not accelerate until I let off a bit to let the clutch grab more!,

I had wondered if it could be a cable adjustment but I have no play in the lever so???

I am making an adjustment to the cable to see if I have it TOO tight, will try the bike again in the morning and post what results i have!

Mine may vary a bit because of the gsxr lever and what not, when I installed the cable I had one hell of a time getting the cable attached to the gsxr lever so it was very tight! (Also it was slipping when I was under a harder acceleration around I'm guessing 5k or so)

Keep in mind there is more to adjusting the clutch than just turning the thumbwheel at the lever. Use the manual to ensure you adjust all 3 places. Ed

Yep of course! Bout to make some adjustments now.

Clutch push rod adjustment -- Need and Purpose
[This is a 1 minute job from start to finish, maybe 2 minutes the first time.]

The FSM covering Z1 and KZ900 includes a periodic maintenance chart requiring clutch push rod adjustment at 2000 mile (3000 km) intervals and explains the need therefor in separate text, which explanation is quoted verbatim as follows:

Besides cable stretch, clutch plate wear also causes the clutch to go out of adjustment, with a decrease in push rod play. Due to this wear, the push rod gradually moves closer to the clutch release lever (at the lower end of the clutch cable) until it touches the adjusting screw. When the rod is touching the screw and therefore has no play, the clutch will not engage fully and clutch slippage will occur. Note that the clutch push rod does not necessaily have play just because the clutch hand lever has play, and so hand lever play alone cannot be used to determine whether or not the clutch requires adjustment.


The FSM covering '77-'79 KZ1000's includes a periodic maintenance chart requiring clutch adjustment at 5000 km intervals, and explains the need therefor in slightly different language, which explanation is quoted verbatim as follows:

Clutch plate wear also causes the clutch to go out of adjustment. This wear causes the play between the push rod and the adjusting screw to gradually diminish until the push rod touches the adjusting screw. When this play is lost, the clutch will not engage fully, causing the clutch to slip.
NOTE: Even though the proper amount of play exists at the clutch lever, clutch lever play alone cannot be used to determine whether or not the clutch requires adjustment.


While the clutch may indeed be worn out with plates needing replacement, it isn't uncommon to overlook or be unaware of the clutch push rod adjustment feature, especially without a manual. It is worrisome to see anyone of unknown experience, without a manual or failing to consult a manual, proceed with clutch disassembly and plate replacement, without first being aware of and considering the clutch push rod adjustment.

Where both (1) clutch cable slack adjustment is perfect, and (2) clutch push rod adjustment is perfect, and the clutch still slips, suspicion is certainly toward the plates being worn and needing replacement. But other things can also cause slippage, even with proper adjustments and good plates, such as glazed plates or improper oil being used in the crankcase.

Good Fortune!

Clutch push rod adjustment is a routine maintenance item explained in the service manual.

Assure having some "slop" in the cable.

Removing the access plate should reveal the adjustment screw and locknut.

First, slightly loosen the locknut.

The hidden end of the screw interfaces with the push rod.

The basic idea is to lightly seat the screw against the push rod, then back the screw 1/4 turn away from the push rod, to thereby provide a small gap between end of screw and push rod.

Here's a possible snag ---
The screw is part of an actuator assembly.
On some designs (screw-type), the screw turns clockwise to seat before turning counter-clockwise to provide the gap.
On other designs (ball and ramp), the screw turns counter-clockwise to seat before turning clockwise to provide the gap.

If the attempted adjustment fails when turning the screw clockwise to seat before turning counter-clockwise to provide the gap, try again by turning the screw counter-clockwise to seat before turning clockwise to provide the gap.

Remember to snug the locknut before finishing. Just snug is plenty tight enough.

Lastly, reduce "slop" in the cable to produce desired amount of free play in the lever at the perch.

Good Fortune!

The clutch push rod adjustment is supposed to provide a slight gap between the clutch actuator and the push rod, which assures the clutch plates are fully disengaged when the handlebar clutch lever isn't being squeezed.

A few manuals are incorrect.

Some models are designed to first turn the adjustment screw clockwise until it seats (zero gap) and then turn it counter-clockwise 3/8 turn to provide the necessary gap.

Other models are designed to first turn the adjustment screw counter-clockwise until it seats (zero gap) and then turn it clockwise 3/8 turn to provide the necessary gap.

If the procedure as prescribed in the manual fails to produce proper clutch function, reverse the adjustment screw turning instructions and see what happens.




Good Fortune!