Motor not running at full speed.

[pfost262]

So I am very new at this. I have a 1956 30 HP Johnson Seahorse that came with a boat last year. I ran it once last year (bought it late in the season) and it ran pretty well. Two fuel lines were leaking so I replaced them over the winter. That was about the extent of the work done on the motor. I put it in the water yesterday and it seemed, at full throttle, that the boat couldn't move out of it's own way. I'm no master mechanic so I'm stumped as to what could've happened. Anyone have any punch list suggestions that I could check?

 

[Boobie]

First do a compression check on it. Then check the spark which should jump a 1/4 " open air gap on a spark tester.