I own the Saito 1.8 and have seen the F .90. The max reco. engine is a 1.00,, but my plans are to use a 1.20 4 stroke. I would not use a gas burner,, too heavy,, wayyyyyyyyyyyyyy too much power on the big engines. The plane would be too heavy and / or way off CG. To make a really great flier.. use the Saito. 1.2 Jim