I think you may be confusing two engines! The 2GM and the 2GM20 are the same basic engine bit the 2GM20 was reworked to increase the power output. I am not too sure of the figures for the 2GM but it was about 13hp. The 2GM20 has a max bhp of 18 with a continuous figure of 16hp. The "F" just denotes that it is fresh water cooled.