Reply to "compression ratio"

You should not be losing power valves on a BG-Holley to backfires. Unless I'm terribly mistaken, all Holleys including tuner-carbs built since about 1980 have an anti-backfire checkvalve built into the throttle base. The ball-check is retained by the body-to-throttle base gasket. This mod can be added to older units with little cost but some effort, as well. Many years ago, I used an old bicycle ball bearing and a small drill to create the required passage in a 1969 Holley. I'd carefully check to see if your base gasket between body & throttles is blocking the check-valve hole.