The pistons are about 0.025 in the hole-flattops with 64cc chambers, bore is 4.06, I didn't calculate cr, I figured it was around 10 to 10.5. Will the large runners cause a rich condition? The only way I think it could is if the fuel come out of suspension and is accumulating and running down the runners causing the richness after its driven a few miles. I 'm going to try an edelbrock 600 carb today and see if anything changes. I'm also going to adjust timing using another method, vacuum gauge instead of light, I think the marks on the new balancer or timing tab are lying to me. Wish I'd checked when I was degreeing the cam.