Why does my 14.5HP Briggs and Stratton engine keep flooding?

I switched engines on an old riding mower. I took out a 12.5 and put in a 14.5 that is supposed to be good. I put the 12.5 carburetor on the 14.5 but it will not start due to gas flooding the combustion chamber. The spark plug is wet and the engine won't hardly turn over because gas is getting into the cylinder. Is it flooding? How do I adjust this bad boy so I can boast about my $90.00 investment.