Hmm, I didn't try new rings or the new piston. The piston and cylinder walls had some gouges.
Pretty stupid on my part, but it was hard to resist the temptation to hit the powerband :D
How's your idle? Maybe you're just running too lean with the throttle closed because of an airleak, or because there's no idle mix adjustment on the bing? I somehow ended up with an airleak at the clamp on both the bing, and the SHA carbs.
When I let off the throttle from 1/8 to idle, it would take a while for the RPM to drop.