Backfire at throttle-up

Hi there. My 75 spider backfires thru the carb just as I throttle-up post shifting, has poor power, spark plugs covered with light black soot. Timing marks all at TDC and has good spark.
Here is a little history on my car. It started life as a California car, now emissions stuff all removed. Switched to 4-2-1 exhaust and no cat, converted to electronic ignition (mechanical advance), added a 34 ADF carb.
I've tinkered with it for some time and cannot figure it out.
I thought maybe the timing marks on the old belt cover might be different from the current one or that the timing mark on the exhaust cog wheel might be different from the old one (pitched the old stuff before comparing).
Do any of you have some ideas why this car is backfiring, etc..
Thanks in advance.

Probably running rich is my guess.

presuming you still have the factory engine...

after removing the emissions equipment, you certainly need to consider re-timing the engine. you may also need to change the fuel mixture to something leaner, since (guess what) the emissions equipment robbed performance...

the book calls for 5 degrees BTDC, but i generally run at 10 degrees BTDC which should be measured with an engine at operating tempurature with a quality timing light.

yea set your ignition timing. all you need is a vacuum gauge.