1974 Mercury 50 Balks when warm

[Dlancer7676]

I have a 1974 Mercury 50 hp. outboard. Getting ready for the Spring fishing, we started the engine, using Mickey Mouse ears for cooling, in the driveway. It started right up and ran and accelerated very well, forward and back. Then we took it to the lake and put it in the water. Again, it started right up, went right into gear, and ran beautifully at high speed and low. Then, just to test the starting, I stopped the boat and turned off the engine. It would only start to an idle, but whenever I put it into any gear and gave it some gas, it died. We were able to idle it, put it into gear at an idle, and idle back to the dock. But the engine would not fully start back up to where I could put it into gear and run again, as it had previously. Any thoughts? It has done this numerous times before so it isn't a new problem. We have used engine cleaner in the gasoline to try to clean out the carbs, as if that might be the problem. A friend of mine who is into older cars said the older cars with coils used to do exactly that when the coil got hot, they would stall out.

 

[merc850]

When you run it again put a timing light on any spark wire and when (if) it quits crank it over and watch the light. Have you checked the distributor cap and rotor for corrosion, there is a carbon contact in there for the rotor.
Undo the brass bolts at the front of the carbs and pump the fuel bulb - gas should come spraying out.
Is the fuel tank filter clean?
Post some close-ups of the front of the motor, cowling off.