I suggest that you calculate your theoretical compression ratio mathematically and see if it comes in at 7.5:1. You can assume that you yave 76cc heads or you can remove them and put a plastic plate on the heads and fill them with antifreeze until you prove what the actual volume of your heads is. Then calculate the volume of the cylinder in the full up position and add to it the head volume considering how much deck clearance you used and gasket thickness. Then calculate the volume of the cylinder in the full down position. Divide the smaller number into the larger number and this is your theoretic compression ratio. Since you have flat top pistons, you don't have to consider valve notches or raised deck, but if you had them, you will have to add and subtract volumes for these piston features.
Before you do any performance engine build up, you should go through this exercise so that you know what you are building.
At 100 pounds, you are lucky it is able to idle! It could have been worse, you could have put a set of 58cc heads on a set of raised deck pistons and ended up with a diesel.