Low compression zn750-A2

Hello all,

I did a compression test on my zn750-A2 and got readings of 110-115 psi across all 4 cylinders (1&3 110 2&4 115)
I suspected this was due to my battery being a bit flat so charged it up and compression improved to around 120 evenly across the cylinders. 

but that’s still low isn’t it?
I'm led to believe it should be 140-170.

what’s likely to be causing this?
If it’s the rings then surely it’d be a particular cylinder not such a consistent reading across the 4. 
I was thinking maybe cam timing is slightly out and the valves around fully closing?
 

Have you checked valve clearance’s as this will effect it if too tight. It is normal to be a bit low on a “mature” motor due to general wear and carbon on valve seats etc (some of the better fuel additive system cleaners do actually work to remove carbon and improve sealing)

Was the engine warm? Was the throttle held wide open? A cold engine or throttles fully or partially closed will give very low readings.

Cheers Tex,

no it’s basically a bare engine, no ignition system, carbs or exhaust. 
I’m building a hardtail and the frame is going for welding next week so was taking the engine out and I thought while I have the engine out I could rebuild top end if necessary so I decided to compression test before I pull it out the frame. Do you think it’s safe to say that given it’s cold and what not that those readings are catastrophically low?

For a stone cold motor your readings are fine. Change the oil and give it a coat of paint 

Sounds perfect to me! 
took the rocker cover off though so now have to wait for a new gasket to arrive but means I can send the cover away to be painted red!

Probably worth checking the valve clearances while it's off anyway (good practice)