If you have enough ground speed to get it airborne it will fly but on the sluggish side. A plane weighing in at 13 lbs would qualify for a small gas engine a lot better than the 91 FX 2 stroke glow engine. Go any larger on a glow engine and you'll be going through more glow fuel than you ever wanted!

The "gas" engine below would pull your plane around with no problems much better.

http://www.horizonhobby.com/Products...ProdId=ZENE26A

The engine recomendations for that plane are....2-stroke 1.20-1.60 cu in (20-26 cc) or 4-stroke 1.20-1.80 cu in (20-30 cc) glow engine, or 25-35 cc gas engine

The 91 FX is on the extra extra low side.....good luck