I dont have a 90 horse mine is a bit bigger but i use a trolling plate they run about $110 but i can get it down to 1.5-1.8 with no problem but always take an extra set of spark plugs for they might fowl out after a while .

Cabellas ,bass pro ,. They all sell them watch what size you get
there are 2 sizes 90hp and lower and over 90 and up my guess is that either way you are ok 90 and up or 90 and lower just check to make sure.

Good luck!!