The left hand port is still the one you're going to want to use. Not sure what your initial timing is set at, but if its 10* or more you can just disconnect and plug the vacuum advance until you get the carb closer. I run 18* initial timing and 38* total mechanical advance, with no vacuum advance on a pretty much stock 318 with good results.
I sent you a PM, but a 750 cfm carb on a 318 is pretty big, you're probably getting too much fuel on acceleration, and its backfiring due to a rich condition on deceleration.
