Here is one for your 4-cycle experts. Can you run a 4-cycle engine one suction? I have a non-flying application were I cannot pressurize the tank or run a pump but would like to run a 4-cycle engine in place of a 2-cycle if possible. All the set-up I've seen for 4-cycle engines have exhaust pressure on the tanks.
A second question - approximately how much longer will a 4-cycle engine of equavlent output (assuming the 60% displacment formula) run compared to a 2-cycle engine on the same volume of fuel? I'm not looking for hard numbers here - just a rough estimamte.