I sure do like the idea of that type of motor. I wonder how much power is lost though?

Long tails like that are slooow. Used to have a 24hp Honda on my 1648. It would top out at 20 with just me. Now have a 35 surface drive and it tops at 27

Power loss? It's direct shaft. Although I don't know of a way to measure brake horsepower, there is no transmission loss as I understand because it's direct shaft, but I may be wrong.

There are plenty of guys getting 20 mph with longtails like this from simple 6.5 hp powerplants like this: because it uses a go-kart powerplant you can hot-rod it just like you would a small-block 350. Considering I can build one of these for less than $600, then modify it to produce twice as much horsepower, it's not a bad deal.

There's also plenty of guys running V-twin 22 hp longtails running 25 mph. That's more speed with less horsepower:



Here's a guy doing about 90 mph. This is a jet ski engine though, but longtails are not slow: https://www.youtube.com/watch?v=5TcxQyqGF-A