A couple of washers under the right side of the engine mount worked for mine. Solved the hard pull to the right on take-off, and also the roll-out while trying to do a loop.

Take your plane up and see how it loops both under power, and in a glide with the engine at idle. If it rolls out under power, but tracks straight in a idling glide, then you need to shim the thrust line a bit.

Hogflyer