When choosing an engine for your ARF, make sure the fuel inlet on the engines carburetor will line up with the output fitting of the fuel tank.

Some ARF's have the fuel tank located in such a position that some engines wont run correctly with, unless of course modifications are made and the tank is relocated.

As an example, I built ( ahem...assembled ) a .91 size pattern plane. Recommended engine was either 4 or 2 stroke. I chose to run the 2 stroke. The fuselage/tank installation was designed for a 4 stroke specifically! Major surgery was required to relocate the fuel tank to get it right!