I am just trying to throw a few things out to possibly look at, so if you have, then please ignore.
It the vlave timing right? In other words, is the intake valve opening when the piston is travelling away from the valves to let the air in the cylinder? If it isn't, you won't get much compression if at all because you aren't filling the cylinder with air. The exhaust valve must be closed during the compression stroke or the air will simply leave the cylinder. Another thing that seems to be a potential issue is the valve seats. Are the valves sealing on the seats? And the last item is the valve body and the cylinder... Is that connection air tight?
How much clearance do you have between the piston and the head at top dead center? If you have an abundance of space left over in the cylinder, the compression will certainly suffer.
If all of the valves seal, and the timing is right, the piston seals to the cylinder walls, and your compressed volume is narrow, then you should have compression. Somewhere there is a leak. You might be able to use some soapy water to find it.