Having run perry pumps and getting frustrated I can tell you that unless you buy the carburator that perry recommends and supplies, you will have problems. They do not take the place of muffler pressure! As an example, I had a Nieranji .40 (japanese rarity) which I ran with a pump and the stock carb and it would run fine on the ground but midrange was awful in the air. After getting the perry carb recommended for the size engine concerned it ran as sweet as my Jett .46 and that's saying a lot! The pumps are designed to run with a needle that allows much less fuel in during midrange. The shape of the needle is what make the difference. If you go pump, go all the way and get the carb!

Good Luck
Max