Stalling under light throttle not full throttle

[WH23G3G]

So on this 65 Valiant 170 after warming for 15 mins, choke opened under light throttle it spits and sputters. Sometimes it will stall out too. It starts back up easily. If you stomp on the gas full throttle it spins the tires and takes off. It also idles back down normal when you let off the gas. I've played with the mixture and it's as smooth as it can get. Timing was at 2.5 degrees now closer to 10. Idles great. Could it have a vacuum leak when in drive but not so much in park? Vacuum is 16-18 in park and drops to 13-14 in drive but needle is always steady not jumpy. Carb is less than a month old.

[moparnation74]

Place your hand or a rag over carb while running to check for a vacuum leak.  Curious if it is a lean condition or a float level issue.