I sounds like there may be an air leak in-between the carb and the engine. Check all seal and gaskets on the engine. T
Check the timing it can be part of the problem. I have V2 with rear carb and works quite well. only proble I have is with the stand off bolts comming loose. I have tried lock tite with lock washers. My friend shugjusted I clean any machining oil off the threads in the stand off witch could be my problem.