Stop in for a cup of coffee

straightlinespeed said
3:23 and that was changed from 3:73. I've never gotten good gas mileage and Im stumped why? I was thinking the large (750) carb was the issue, hence why I swapped to the 600. But swapping to the smaller carb slightly improved it. Thinking about it if Im really easy on the throttle I can get maybe 120miles and that leaves me with a quarter tank of gas, but I dont know how accurate my gauge is so I dont push it. At 60mph, Im turning 2800rpm, at 70mph Im turning 3500rpm. I only have a 26.4" tire on the rear. So if I could get a taller tire that might help some also.

The engine is an air pump so at a fixed A/F ratio, carb size doesn't matter for fuel used. A/F ratio determines the amount of fuel used per each revolution. If you are using more fuel than normal A/F ratio can provide to maintain a certain RPM, the rest of the drive train is providing resistance making more fuel necessary to maintain that RPM...or you aren't using the fuel efficiently (low MPG)

A 42 RH with a 0.69 OD gear will increase MPG only if you don't need to pour in the extra fuel to maintain the drive power to maintain speed. The risk is that the OD will actually be less efficient than a standard 1.0 top gear if it needs all that extra fuel.

I suspect your timing curve is way off so that you aren't using the fuel you are delivering efficiently...and just blowing it out the tail pipe instead of turning it into power.