i have a 72 demon 340. when i bought it it had a single plane with a 750 double pumper and a mp508 with a 3000 stall and 391 gears. it ran strong but lacked any power below 4000. i put a crosswind airgap and a 670 quickfuel tech carb on it. it really helped the bottom end. i didnt notice any loss of power on top since i shift at 6600.