The Hog Air line of engines are running a Harley carb, but I don't know the size. I personally would pull that prop and see what rpm I could get with just the engine being careflu not to redline the motor ( the same as revving it in neutral ). If you can get close to redline with say half to 3/4 throttle, I would think that the carb is sufficient. The math formula for calculating CFM size of carbs is: street carb = rpm x displacement (in CID ) divided by 3456 x 0.85 = cfm size carb. Convert square inches to square centimeters CC x 0.0610237 = CID My engine: 1915 cc x 0.0610237 = 116.86 CID Now take CID 116.86 x 3400rpm = 397,324 / 3456 = 114.96643 x 0.85 = 97.721465 or simply a carb rated for approximately 98cfm. That is measuring the engine output at a standard auto engine efficiency of 85%, not 100%. At 100% you would use the 115cfm figure before the last multiplying. Unless you are using a racing engine it is always better to go at least one size smaller carb due to the fact that the engine cannot reach the rpm necessary to use the air available at wide open throttle, and therefore will SLOW DOWN at wide open throttle not speed up. I have proven this on the drag strip changing from a dual plane intake to a single plane intake which effectively went from cutting the carb in half, to giving every cylinder access to the whole carb. The engine would actually nose over and start slowing at wide open throttle compared to running faster at 3/4 throttle. Also not having some engine heat applied to the mix is only good for wide open throttle, and not acceptable for part throttle operations. You will fight a rich/lean mixture problem if the incoming charge cools the air/fuel mix enough for the gas to begin condensing on the intake walls and then get sucked in by the next cylinder. Things that effect volumetric efficiency: air filter, restictions in intake system, exhaust restrictions, valve train restrictions, cam design, and whether the carb can fully open at max throttle position. The manufacturer should be able to give a guidline as to what CID/CC size engine the carb is designed to support, and what the cfm rating is for the carb. It is also possible that your prop is pitching out to beyond 48 too early if your engine will not rev up. That is what was happening with mine and I had to go down to a 44 to get 47 to 48 inflight at cruise. FLY SAFE! Colin & Beverly Rainey Rainey Mortgage Professionals, LLC crai...@apexlending.com 407-323-6960
