hello I just bought a new zero with a 21 hp kaw on a 48" ferris IS 1500 and was looking at engine ...seems to be the same dispacement as the 23 with a slight increase in oil capacity. Question I have ,,,is for option someday, if I feel I need extra power for mulching,,Is the only difference a larger carb ? Is that how they are boosting up two hp ? will the larger fit the 21 ? Prolly cost 400 biscuits or so ??? thanks already rt... my theory is if the engine works less it will run cooler there for last longer ???