Re: Carb ID?
noelm
You're not totally wrong, but almost. If there are difference, no one has been able to tell me what they are. The bore x stroke is exactly the same. When comparing the 2 intake manifolds the cyl end port diamaters are identical, which tells me that the jugs/ports on my 20 were intended to flow the same volume of air as whatever this larger manifold was bolted to. The bottle neck is the carb and carb end of the intake. While I've never checked part numbers, I can not imagine that the manufacturer made several different strength pistons, conrods, cranks etc all of identical size. Production costs would dictate that you make one to fit all applications. All this plus a factory trained tech telling me that the induction is the only difference had me convinced to go ahead. Increase in performance? Huge! My "20" hp mounted on a 14 ft Lund with 3/4" plywood floor, built-in storage, 3 swivel pedestal seats, plywood casting platform etc would do 34 MPH according to the GPS. But you didn't need a meter or gauge to tell you anything. When it was time to head back to camp and you blew past the 25 Mercs on the same boat and squeeked past the 40 Mariner on the 16 ft Springbok you knew you had made a significant improvement. The difference at change was night and day.
My 30+ years as a licensed mechanic has taught me a few things. One is how carbs work. Carburetors meter fuel according to how much air is flowing thru them. Increasing the size of the carb throat does nothing to changing the mixture ratio. That carb is designed to meter the correct amount of fuel for the amount of air flowing through that carb. Guys that fool with jet sizes are at risk of problems. Change jetting according to altitude where the amount of oxygen in a cubic foot of air has changed. Otherwixe ~14:1 by weight is the correct ideal ratio.
Okay, here's where you were right. Fuel consumption. You can't make more horsepower without using more fuel. Likewise, don't expect to trade your 20 on a 35 and expect to see the same mileage. My 250 HP Aurora uses more fuel than my Wife's 150 hp Grand Am. Those are facts of life.
Steve g.
