Define "a little bigger". A cam with a lot of overlap between the intake and exhaust valves pulls unburned gas out through the exhaust valve. It doesn't start running efficiently until the speed goes up- - - -sometimes WAAAY up! One engine I ran on the round track wouldn't run smooth below 3,000 RPM, but it pulled strong from 3K to 8K. Below 2500 RPM, it didn't run rough or stumble- - - -it just shut off! That's an extreme example, but engines with somewhat radical cams don't idle well, and they get lousy gas mileage.
The most common mistakes amateur engine builders make is using too much cam and/or too much carburetor for the application. More is definitely NOT better in most cases.
Jerry
