ORIGINAL: fix-n-fly
I had a K&B .40 back in the 80's for a Great Planes PT-40. We could get the engine to run on the ground, but about a minute or less into the flight, it would die. Tried everything and had a person that was good at tuning engines helping. I've seen people that swear by them and told me that I needed to heat the engine in the oven and do this and that and something else and then they would be a good engine. Frankly, I need something that will start and work in the limited time I have to fly. Switched to OS max (the FP and LA series) and now Thunder Tiger and never regretted it.
The .40 had a ring and was very particular about tuning which made the Perry carb so nice as it tuned easily.
IF you run a .40 lean it will quit (or worse). A .40 with a Perry carb and pump (rare on the .40's) was a very good combo. Most didn't want the extra cost or the room the pump took. This is the pump on the rear of the engine case and NOT the newer separate pumps. I'll be using a pumped .61 in my pusher as the tank will be well over a foot away.