Keep this thing as light as possible and put an OS 160 in it . It will need a $25 pump and it will be the sweetest running engine you own. Prime with about 5-8 flips and put on the glow... starts on the first backflip. Economy? 16 oz tank yields 10-12 min flights easily. Messy, no. Only a slight film on the belly after a day of flying, this aint your 46 FX. Uses $10 a gallon common fuel. A 40cc gas may have a slight edge on power but will be 1.5 to 2 pounds heavier. If its tail heavy, get those servos out of the tail! I'm not down on gas but planes this size need all the help they can get to stay as light as possible. 27% planes are the smallest in my opinion to run gas unless wing loading is not a concern. I think gas' power to weight is too small for the small planes. I know there are a lot out there that fly well, I'm just a "light" freak, and the difference in flight characteristics is night and day.