I have a 2000 15 hp Mercury
and had similar problems, only my wouldn't run unless it was fully choked. Bought a rebuild
kit from Mercury Direct, Marshall , TX and rebuilt the carb and it runs great. You can get the part number off their web site. It will show a full blow up of the carb. Only run non ethanol gas, and when you can't get that use Premium gas, it doesn't have as much ethanol in it. Run the engine
out of gas each time you use it. I assume it is a 2 stroke
engine. Don't let it set up with ethanol gas, the corn settles to the bottom and clogs the carb. Also check your fuel line and if it is older and you have been running ethanol gas in it in the past few years it will eat the inside lining and clog your fuel line. These are all the things I've learned in the past 2 years and it has cost me over $600 to get it fixed.