Low compression

Hi all I have a problem with my z1000st I had it bored to 1100 fitted a set of cruise image pistons and rings, now its hard to start doesn't idle well, I've check valve clearances check valve seats, carried out a leak down test,but compression is around 120psi across all four cylinders remove the head again and noticed that at individual  top dead centres the pistons don't go to the top of the cylinder, heres  a picture is this normal?
Any advice would be appreciated.

Most engines run with a positive piston deck height [below the top of the cylinder block].
How thick is your base gasket? Have you considered using no base gasket just sealer?

To be honest if you have 120psi on a freshly bored cold motor I think your problem probably lies elsewhere. Is the cam timing correct ?
PS: are the ring end gaps equally spaced 120 degrees apart ?

You don't say if that 120psi is hot or cold engine or throttle open or closed.
If that's cold then it's not too bad. 
If that's throttle closed it's bloody brilliant. 

What type of compression tester? The type with a rubber end that you push on? Or a hose type?
If its hose type does it have a Schrader valve on the threaded end?, If not it'll read low as the hose adds volume to the combustion chamber.

Am I the only one that's seeing small bits of alloy around the edge of the piston ?  I hope that was all cleaned out...

Also not mentioned is how much breakin was done to seat the rings  after  motor was built 

wrote:

Am I the only one that's seeing small bits of alloy around the edge of the piston
?  I hope that was all cleaned out...


I saw that too but hoped that was small debris from pulling the head back off  ( Hope , hope , hoping  )
 

wrote:

wrote:

Am I the only one that's seeing small bits of alloy around the edge of the piston
?  I hope that was all cleaned out...


I saw that too but hoped that was small debris from pulling the head back off  ( Hope , hope , hoping  )

 

My guess was gasket material. 

wrote:

Am I the only one that's seeing small bits of alloy around the edge of the piston ?  I hope that was all cleaned out...

Look's like gasket scrapings to me but I have old eye's 

With stock pistons the perimeter of the piston should just reach the top of the cylinder.  So what you're showing in the photo is not normal, but those are not stock pistons if you bored to 1100.  That said, 120 psi is a good reading, maybe a tad on the low side, but more importantly they are all within 15 psi of each other so it seems that your rebuild is OK.

As far as poor idle is concerned, what changes were made to your fuel and air circuits?

Isn't it true that the piston crown height is lower on an aftermarket piston to allow for planing the head?