manual says136 to 209psi, 1981 kz650 compression

Could be that if your stickers under the seat are intact, the recommended Octane could be there?

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You also have to take into account altitude. I live at 4300 ft elevation and my comp readings are lower than the manuel indicates.

martin_csr wrote: From the 1981 KZ650-CSR owner's manual:
Use a gasoline with an octane rating equal to or higher than that shown in the table below.
(RON+MON)/2 => 87
(RON) => 89

OnkelB wrote: To add to the confusion, my Clymer manual :blush: lists three different compression numbers for the KZ 650s:

- 1977-80: 170 +/- 15 psi (12 +/- 2 kg/cm2)

- 1981 : 136 - 209 psi (9.6 - 14.7 kg/cm2)

- 1982 on: 100 - 156 psi (7 - 11 kg/cm2)

Never noticed these differences before, weird indeed.

I have the Kawasaki FSM for the 1981-82 KZ650 which covers the D4,F2,H1 & F3,H2 models.

Pg 3-8 Table 3-13 shows 136 - 209 psi (9.6 - 14.7 kg/cm2) for the 81 models.

In the supplement for the 82 models, Pg 9-15 Table 9-8 shows 100 - 156 psi (7 - 11 kg/cm2).

☨ Engine hot, spark plugs removed, throttle fully opened, cranking the engine with the starter motor.

Wow, the high limit of 209psi in my '81 bike dropped over 50psi to 156psi in the '82 kz650 -- my '81 has a 2-valve-per-cylinder head -- is the '82 bike a 4-valve head, I'm just wondering, since that's a big psi drop and a total head re-design might help to explain it.

On the altitude, yep you're right, you're almost at 'mile-high-city' of Denver altitude at 4900 feet, the air is much less dense and much dryer there. I'm at sea level, I wonder since the bike's are made at sea level in Japan if the fsm compression is based on sea-level readings, I'm thinking 'yes' most likely.

The seat bottom has 2 stickers, on is white with a line drawing of the bike and arrows pointing to everything they want you to check on a regular basis, no gas octane though, and the other sticker is a small black one for the oil type, no gas there either, good point about the stickers though, I'll check the rest of the stickers I can find, although it looks like Martin found it at 87 or 89 octane.

At 200+ psi, aren't we talking high compression/detonation issues? And on a race motor isn't the octane real high to stave off detonation? I'm not an engine guy, but just wondering, 87 octane at 200psi is surprising.

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martin_csr wrote: Nope. Same basic 650 engine.

I kinda wonder if the wrong compression table was placed in the FSM for the 81 KZ650?

What's the compression on bigger bikes?

Wow man, same 2-valve engine in the '82 kz650?!! Wow. Well it goes back to my opening
post, whether my 1981 CSR kz650 fsm is wrong on the compression numbers.

My kz1000 1978 factory shop manual, this motor as we all know is also a 2-valve-per-cylinder motor,
calls for a range of 128 to 156psi per bore, with a lowest 'service limit' of 100psi.

I think at around 150psi per bore on my cold compression test yesterday, my engine's looking better all the time. I'm headed over to the shop now to heat her up and re-run the compression test when hot.

Okay, the results are in, just had a nice ride through town, hit all the stop lights, got on her on some backroads, then did the compression test:

(1) 156psi (it read 143psi cold)

(2) 159psi (read 150psi cold)

(3) 160psi (150psi when cold)

(4) 156psi (147psi when cold)

She came up a bit.

I also found another sticker on the bike, under the seat on top of the rear 'inner fender', it calls for '87 octane or higher,' good call there Motorhead.

This bike has 17,329 miles on it and runs strong, nary a hiccup anywhere in the rpm range, lots of power for a 30-year-old air-cooled 2-valve 650. Not burning any oil.

I'm satisfied, my Kawasaki factory shop manual has incorrect PSI numbers.

Probably Martin's numbers in his '82 kz650 are the correct ones, 100 to 156 psi.

I guess my valve seats and valve clearances must be in excellent shape.
I'm still gonna pull the valve cover and check clearances though.

I wonder if the high point of that spec is a miss print. There are other errs in Kawasaki and many other service manuals, the later printing may be the correction. 200+ psi on 87 octane, seems a bit far fetched.

IIRC the claimed compression ratio for the 76 thru 81 models was 9.5:1 and for the 82 and 83 models claimed ratio is 9.0:1. This might explain why the 82 numbers are lower than either the 77-80 or 81 numbers. But I can not explain why the 81 numbers are so high.