[*13*]

You are down two sizes on your main jets "may" mean that you are dumping too much, too fast from the nozzles into the carb causing a slight bog. I agree that you may need more fuel but like I said, it's tough to say without knowing everything. Try bigger first. If that does nothing positive, go smaller.
I didn't notice that you have a vacuum secondary carb. That also may be a cause. If you can't get the secondary to open correctly with the proper spring change try a double pumper :0)