Hello;

Took the new Roadster out for the first ride, sunny day in Tomahawk, Wisconsin. Finished the build over the winter. No problems except for backfire on the start of acceleration and lots of backfiring off throttle, deceleration. Here is the skinny:
302 H.O. stock cam and heads. Zero miles on engine.
Timing is 14 at idle (800) and advances to 38 (3000)
Timing order checked for a H.O.
Carb is a Holley 80457-10 600 CFM and vacuum secondaries

All cylinders are firing and it idles great. Could it be float level or power valve?

Any help would be appreciated. Thanks