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Discussion Starter #1
I love this bike (ZZR-600 aka ZX600J), really does run great and doesn’t give me grief. So I’m not sure if I should bother tearing it down to investigate what’s up.

If I check compression when the bike has been sitting for several days, it’s about 135-135-65-135 (cyl #3 is way low). And there’s a noticeable misfire for the first 1/4 mile of riding. That’s it. Once warmed up, it runs perfect. And when fully warmed the compression is closer to correct - about 140-140-125-140.

Cams and valve clearances are normal. Odometer is 31,000 mi.

Maybe this winter I should take off the head and check it out further. But what’s the down side if I just ignore it & keep riding? It’s been like this for years.

Thanks
 

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That is a huge desparity when cold, less than half the other 3 cylinders on #3..... and then they don't go up much when hot? except number 3..........

I would do a leakage test and listen to where the compression is coming out (crankcase breather?, airbox? exhaust?) then you will know where the problem is

it could be bad rings, it could be carboned up valves it could be worse.....

I suggest finding the casue and then taking appropriate actions to remedy

fyi........ My 07 ZZR600 has over 175psi compression on all 4 cylinders when cold with 99,800 miles on it........ it goes up to over 200psi when the engine is hot (but I am runnning with no base gasket too, which likely accounts for 10-15psi))
 
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Discussion Starter #4
Thanks for the reply. It’s cool that you have the same bike and it’s going strong at 99K! I hope to get there.

My numbers from memory were a bit off, when warmed up, it’s actually at 155-150-145-150. Though these numbers look basically good, it’ll consistently have the stuttering misfire when started cold after a few days of non use.

I think I’ll invest in a leak down tester and run all the tests and see what’s up.
 
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