15 hp mercury outboard

Question

I am unable to idle. It start in a racing position and when I try to decrease acceleration it shuts off. Even when it's hot it still races.

Answer 1

Have you checked that it adjusted correctly at the carb.  It may be that the idle position on the throttle control is actually closing the throttle right off.  

Answer 2

Do not put carb cleaner in the fuel of a 2 cycle motor. It prevents the oil in the fuel from lubricating the cylinders and you will end up with damaged cylinders. Have the carb checked or removed and cleaned if needed

Answer 3

If you left the fuel in carburetor over the winter:

There are many additives in fuel now. Some of them dry and block small channel in carburetor if engine is not used for prolonged period of time. Some of the channels are necessary to balance the performance in low RPM.

How to fix it? You may need to have your carburetor cleaned, but I would start by adding a carburetor cleaner to your fuel tank and running the engine for an hour. Maybe the simple solution will help.