The 75 is a great engine for a 40 size plane and will run with the best of them. It is a very tight engine when new and will require a little breakin time but oh boy when this thing lets go you will be pleased. Just use a little JB Weld to hold the muffler together at the joints. I like the 12.5X6 prop the best but it will pull the 13X6 very well. The engine is a little sensitive on the needles but with the tuned muffler you can expect that (not as much back pressure as a quiter muffler) and the needles will need to be set properly or it will let you know. My 75 would run rich but would gurgle on transition. I tried a smaller prop on the 75 but it didn't like it so I use the 12X6 to 13X6 prop and it is very happy. I think the small prop required more fuel than the carb could deliver (too many rpms).