Can’t you leave the engine cover on and squirt the gas in the carb through the little front door? If the flywheel explodes and comes through that and kills you, your days were up, anyway. Come to think of it, can I do the test FOR you? Then I won’t have to watch the TV news anymore.

Running the test wheel on the boat in the water actually works best… Usually, water just splashes out of the test tank causing the engine to ventilate, and RPM to fluctuate quite a bit….This will just add more confusion to your issue. I realize that getting the boat to the lake is a pain, but it is the best test method…

Looks like a lot of discussion has taken place since my last visit, so let me clear up a couple of things.

The flywheel that blew up was on a race engine. The guy had machined off a bunch of metal to lighten it. Live (maybe) and learn.

Test props. They work by the fins grabbing water and flinging it against the outer rim by centrifugal force. The faster you turn it, the more water fling. The result is forces that are working against themselves, like trying to pick up a chair while you are sitting in it. Also, the fins are angled and do provide a bit of forward thrust like a regular prop. This is necessary to keep it in solid water and not just sit there making a hole to cavitate in. The forward thrust in small in a 6 hp, but a big V4 moves a lot of water. No way in hades can you run a V4 at WOT in a trash can, test prop or not. Likewise, test props are matched to horsepower. For instance, a 28hp is different than a 35 hp, which is different than a 40hp, although they all fit the same shaft. And yes, they work best with the boat launched and tied to the pier. Since our shop was land-locked, I had a full set of test props up through 200 hp when I was twirling wrenches for a living. And a large professional test tank. Even so, I couldn’t run a 200 in it at WOT. Too much air mixed with the water.

Posting the last list that I have.