I have K&B .61's with and w/o Perry pumps and do get a bit more power from the pumped engines. They use carbs with slightly larger bores too so this also helps. Remember these engines are just air pumps so if you can get more air in/out you should get more power. With more air you need more fuel to keep the mixture right so you may need a pump to keep up. The K&B pumpers run great in all positions better than the non-pumped. I'm working on a pusher right now and the tank will be almost 2 feet away. I've bench run this arrangement with the pumper and it runs well in all attitudes.