RE: More Rio 51 woes.
Mart's right. make sure you prime it til it pops. If you do flood it, you can take the plug out and turn the boat over and pull the crank to get the fuel out. Then it usually will start first pull.
A mistake I used to make is not having the idle set high enough. You can adjust that with your throttle trim.Sometimes I will open the throttle about 2/3 and turn the rx off to keep it open then turn it back on after it cranks.
I would definitely check out the thread Dreamin suggested.