I had no prob with down low RPM and Mid RPM with stock carbs. The big thing on dual carbs is having they synced. If they are not sycned, then you will have one hell of a time with the low end. I would just put your money some where else like a timing plate, intake-filter/s, suspension, cool head and or porting.
If you have not yet done a +4 deg on the timing. It will help much with the low end sense you dont see very high RPMs.