I think I have the same problem MM..I've run out of gas a few times without the reserve light coming on or I don't notice it in time (although I think it does'nt come on. Last time I ran out , i put gas in and tried to start and it would 'nt turn over (as if the battery were dead) Finally started after it cooled down for 20 min or so. Still not sure of the cause
Do you have a lead acid battery.
Mine was doing the same thing and it turned out the center cells on the battery were only half full. You can't tell if they have the right levels by looking down in the holes.
I would take the battery out and check the acid levels.
Course disregard if your using a sealed or jelled battery!