I don't know about the hydrofoil but my boat motor has a steering-dampener-adjuster thingy on the bottom of the Anti-cav plate at the rear of the motor. It is also the anode. Yoou just loosen it and turn it to get the boat to trck straight, maybe yours has something similar.
I had a hydrofoil on my last motor and it really caused it to pourpus bad. I had to move the fuel tank to the front of the boat. It did plane faster though.