82/83 GPZ N1 750 top end kit/tips

Going to just rebuild, compression test is horrible, as long as head is okay, going to do whole top end. Any kits for the 750 N1 motor, pistons, rings, gasket set, that would be recommended? Also should I have any machine work done, and any timing adjustments that would need done if anything is machined? Vacuum sync showed little to no vacuum on cylinders 2 and 3, about 70psi cold, and 1 and 4 were about 115 on compression check cold. Any other recommendations are welcome. The bike is titled as an 83 Spectre 750 Shaft but Vins on bike say 82 N1.

How many miles? Valves adjusted?
Steve

27k. I Cleaned carbs, Only 3 exhaust valves were out of clearance, had to go 2 shim sizes smaller. Was going to re time cams to make sure thats not the only reason for the low compression, vacuum, and idle to all rpms, runs rough. Good spark and all electronics. Put a manual tensioner on. I didn't run to tdc 1 and 4 and check cam timing when I did clearances, just zip tied chain to gears and puts cams back in. So before I pull the head and all that, going to pull cams re time, and go from there. If I do need a top end done, and bigger pistons, would I need to time cams or jet carbs or both?

Reset the timing yes. Just a freshen up everything else should stay the same. Bigger pistons and better cams = more juice. It might start running better with the valves adjusted.
Steve

Has low compression and vacuum on cylinders 2 and 3 1 and 4 good vacuum but low enough compression also. Valve adjustment did not help. It either timing, valve seat or piston rings. Like I said Will start with timing, and hope I don't need new rings let alone pistons if I need to do a rebore. Basically know what I'm doing as to diagnosing. Wanted information on good affordable top end kits if I do that this year, and if I have to get a big bore kit, if I'd need to retina cams differently than stock and mess with carb jets. That I do not know. I've heard if you plane the head, have to set timing differently. Jesse

The valves may have burned due to maintenance neglect. Not adjusting the valves at the prescribed interval in the factory service manual can do that.

Sounds like a teardown and inspection is in order. If you don't have a bore gauge find someone that does and measure the pistons and bores. If there is more than .001" out of round and/or taper in the holes then a rebore is in order.

Assuming the bores are okay then you can bottle brush hone the cylinders and install new OEM rings. If you need a bore job there are various options including a Wiseco big bore kit or one from Cruise Image.

A valve job would be a wise investment. A shop like APE can take care of that for you.

OEM Kawasaki parts and gaskets are highly recommended. Aftermarket gasket kits range in quality from passable to criminally crappy. Considering all the time and energy involved with a rebuild, cheaping out on gaskets is a questionable path forward.

Have you run the bike many road miles recently?

Gummed up rings can unstick themselves just with some miles and maybe a shot of upper cylinder lubrcant or injector cleaner. Bikes laid up for a long time often do this,
My 45k GPz750R1 had just this down to 50 psi on one. Search here for the thread.

When CR testing, did you have the throttle wide open? low vacuum and low compression on the same pots , do more diagnostics before taking it apart. Can you do a hot CR test?

Vacuum sync showed little to no vacuum on cylinders 2 and 3, about 70psi cold, and 1 and 4 were about 115 on compression check cold.

I think he do the compression test on all cylinder at the same condition, (full throttle)
I would pull the cylinder head and fill the combustion chambers with fuel and searching for leaks in the
in- and exhaust ports, specially #2 and 3.

Further diagnostics would indicate if a this is a valve , gasket or ring/bore issue. Just a decent hot wet/dry CR test would be revealing.

This gummed rings thing, as well as my 750 I had it also on a GPz11 motor that had been laid up a long time. Poor compression on all down to about 70 psi...Coaxed it into life with a bit of starter fluid and run it up, hot test better around 120 psi just five mins of running. It is going to be bored out anyway, I just wanted to hear it run before splitting it.

If the motor has been left for a long time in any position then on a four pot there will be two valves open at any time, moisture gets in to the cylinder through the exhaust pipe / carb and open valve. Two pots down points to this -just I would do more before pulling it apart.

Thanks for the info and going to do a hot wide open throttle compression check. Never thought of stuck rings. But going to at least re ring it with oem if cylinders are within tolerance. Need new uppers head gasket anyways it leaks a little and want motor good and clean like rest of bike. 27k on bike, and has been ran. Everyone's advice and recommendations is very helpful. Thank you all.

If I do a big bore kit would I need to do anything to the carbs or timing to compensate for the bigger bore? Or would it be fine as is?

When I went from 903cc to 1015, I didn't change cams and already had a 2/1 exhaust. All I had to do is go up one step on the mains.
Steve