springhillflyer - Which plane are you trying this with? If you are trying this with a NextStar, your have a plane that weighs 6-1/2 - 7 lbs (My Alpha 60 with Evolution .61 weights 7-1/2 - 8 lbs for comparison). It may have a more streamed lined fuselage and a lot of wing, but that is still a lot of weight for a .25 to pull. Now if it was a 5 - 5-1/2 lb trainer like the Avistar or SuperStar 40 that would be a different story. I used to fly a Balsa USA Swizzle Stick (older version of the current Stick Trainer 40) on a K&B 3.5cc (.21) and that was a 4-1/2 lb plane and 3-channels. The K&B 3.5cc is as powerful as the OS .25 FX but I found in almost every case I had to hand launch it when flying off turf.

Are you planning flying this off a hard surface runway or turf? If turf I really question if there is enough power in a .25 to get a NextStar off the ground let alone safely fly it, but the others should work. You'll just have to remember it will fly the way the old planes used to - on the wing. It'll feel sluggish and not want to climb very well, but you'll get some good experience from it.

Hogflyer