For the money, you can't go wrong with the Tower .61, but in that case, you may as well go ahead and buy the .75, since it's only $10 or so more. They're the same engine, just a different bore. You can also try the Thunder Tiger Pro .61. It is a very reliable engine, but not one of the strongest. both brands named are very reliable, and affordable engines, though, the Tower is one of the strongest and cheapest. Just my 2 cents.

John