Seems odd that it 'fired right back up' if the f/filter was empty.....
I have seen that when the FF is mounted horizontally, it can get an air lock in the upper half...but it is still passing fuel to the carb.
This is a back to basics job.
Remove the carb. Check the transfer slot position [ how much shows below t/blades at idle, should be 0.040" or less ]. Check float level, needle/seats & floats for sticking/binding. Unlike brand H & clones, you will not need any gaskets if you are careful. If you have compressed air, blow out all passages.
Also, the RPM intake is a poor choice. You have a 6500 rpm intake & a 5500 rpm cam....