If it is not hooked up to the engine this could be your problem. When I bought mine, someone had it hooded up to the ground on the solenoid and I had similar problems to what you are experiencing. Also, if you have a deep cycle battery you should replace it with a marine starting battery.
sounds like the carbs have to be rechecked, float or needle seat not working, flooding it causing the motor to hydro lock, check out the fuel pump diaphrams again as well, after this stick your finger over the spark plug hole and have someone turn it over to get the gas to clear out of the cylinder, then oil the hole and do the finger thing again, reinstall plugs and fire away
I had a very similar problem with my 50HP force. I had to take the starter out and the bracket and clean in between the bracket and the block. Starters are self grounding so the bracket is the ground for the starter.
