The old gas has shellacked onto the carb.. Have the carb rebuilt.. They will soak it in gunk to clean off the old gas,, and put all new floats,, seals n stuff in it..
With the carb still of,,
Drain the old oil.. Put 4 quarts of kerosene where the oil goes..
Pull out the spark plugs,, and shoot a few shots of penetrating oil into the spark plug holes. (leave the plugs out for now)..
Turn the engine over several times - allowing the kerosene to clean it..
The more you turn it over,, the cleaner it will get..
Drain the kerosene out.. Change the filter & fill it with oil ..
Put new plugs & wires,, new filters,, the rebuilt carb,,
and you should be in business...
..........................................