Originally Posted by kubcat
I think the problem is more likely to be not air pressure but don't know how high to go on the floor and keel.
If you're not sure then the floor is almost certainly not inflated enough. Get that sorted first before you muck about with the engine.
Floor should be something like 10psi which is a lot more than you think it is. Keel doesn't need so much, but does need more than the tubes. Perhaps someone with a similar boat like a Quicksilver airdeck could see what their book says.