How much compression should my 78 KZ1000 have?

Stock internals as far as I know. My plan is to put a compression tester on each cylinder. Then hold the CV slide open with my finger and throttle open, hit the starter button and see how hi it will go. What should I get?

also - does the engine need to be warm to get accurate reading?

I remember (?) the 1000 engine compression was supposed to be about 170 (really good) and maybe 125 worst case ballpark. I believe that's hot readings.

I would check both dead cold/dry and then also hot. A low reading cold/dry which goes way up with a shot of oil in the plug hole means bad rings. Readings that stay low hot means valves probably need work.

Nelson wrote:

Stock internals as far as I know. My plan is to put a compression tester on each cylinder. Then hold the CV slide open with my finger and throttle open, hit the starter button and see how hi it will go. What should I get?

Every compression gage will read a little different. My mint condition GPz1100 with 9400 miles on it reads 125 cold. More importantly my engine reads exactly 125 psi for all 4 cylinders.

I agree with what "bus" said... cold 110-120 for those motors and as low as 100 they seem to run fine - shockingly low when a lot of motors are 170-180.

I use to kick start my 650 at 240 psi, but that was a drag only motor.

anything over 100 pounds it will run but that wont give you a true indication of engine condition for that you would need to do a leakdown test but even if you don't have a leakdown tester you can get a good idea from how even your cylinders are to each other. up to a 10 percent differential is usally concidered allright. i try to do them cold and holding the slides open on cv carbs wont do anything just hold open the throttle, the butterflies have to open on cv carbs in order to allow proper amounts of air in to the cylinders. if your readings are low it may be due to something as simple as tight valves ,misadjusted cam chain.so if the bike is a runner now and not blowing oil i'd do a full tuneup then check it again. the difference between a cold compression and hot can be quite different.MAKE SURE THE THROTTLE IS WIDE OPEN. its really hard to compare different bikes compression figures it depends on cylinder size ,cam profiles, ring condition, and type,cam timing, combustion chamber size and design. lots of things can have an effect

Thanks. it's a very good running engine with 36k miles on it. I'm doing a major custom bike build and trying to decide what (if any) engine work to do. Comp readings will be one of the indicators to help me decide if I should take it apart.

Nelson wrote:

Thanks. it's a very good running engine with 36k miles on it. I'm doing a major custom bike build and trying to decide what (if any) engine work to do. Comp readings will be one of the indicators to help me decide if I should take it apart.

A compression test should be done, no doubt, but if its going to be a major custom bike, it should have a leakdown done no matter what.

Like already said, perform all the major tune-up stuff, especially valves first. Then remove the carbs and exhaust, and put some air in those cylinders. Air will always escape past rings some, and will normally be heard at the crankcase breather. You should not hear any air escaping from the intake/exhaust valves as your tester should indicate.

ME... if it wasnt near new, and hadnt been done by myself recently, then I'm tearing the top off at the very least anyways :laugh:

Good Luck.

yeah i expect to end up removing the top end and inspecting it all anyway. however the bike is not going to be sold and there's no rush to spend money... so I can do whatever is needed any time I need to.

always time to do it right, never time to do it over

36K definitely needs a valve job at least replace those stinking valve seals that always like to go bad and start leaking oil into the spark plugs.

Injected wrote:

I agree with what "bus" said... cold 110-120 for those motors and as low as 100 they seem to run fine - shockingly low when a lot of motors are 170-180.

That is bizarre. I must have been thinking of the 900 (?) or 750 fours but I could swear the full compression was about 170 psi. Even my 750 twin checks in at 155 psi when good.