If the motor has a larger cam you may be to far into the transfer ports at an idle. Easy to check take the carb off and see if the primaries are squared.
If not as seen in many cases. You will need to square the primaries and idle off the secondaries with a 4 corner idle circuit carb. You all will not believe the difference. Accelleration like a two stroke.
You can also bring the idle up with timing to lower the primaries on the carb to square them but then you will be playing with the advance and curve.
Double pumpers without a 4 corner idle circuit are a guessing game at the most.
Bottom line is you either put the cam in for the sound and deal with the dead spot. Or use the cam for performance and idle off the secondaries. This is just the best way for me on all the motors we build that are not injected and have large cams. We sell and use Quick fuel Q series because of the price and they are real close out of the box. Usually no changes needed.
Right to the floor from idle in gear. Not even a Cough. But we do run a little Cough syrup. In ours. LOL