Ready to sink the boat

This is my first time posting something. Here we go. I have a 50 HP Mercury 4 stroke Carbureted engine. This unit was in storage for many years with no stabilizer in it. Once I got it I had the carbs rebuilt and the problems started. Mechanic said there was water in the fuel, so I completely drained the fuel tank. Still had issue. Motor runs great on idle and low speed. The problem starts once the engine warms up and you are going wide open throttle. Engine starts to lose RPM and then just shuts off. I have replaced the fuel pump and fuel line and still the same thing. Compression is good, as well as new plugs in the motor. Measured the resistance on the coils, and they both measure out at 2 ohms. Any ideas would be appreciated.

If I was guessing I would start by thoroughly testing the stator. The symptoms, which could be cause by a few things, are also indicative an issue with the high speed (coils/bobbins) on the stator. If there is a break in the winding(s), particularly once they warm up and the copper expands a bit, they can lose (continuity). If "both" the high and low speed side of the stator is not producing power (above about 3000-3500 rpms) there is insuffient power being generated to supply the ignition.

So if the low speed side of things is fine it "would" idle fine and even putt along fine but once it's opened up and needs the high speed side, if it's not there it will fall flat.

A DVA test to check the voltages at "running speed and temp" with the motor in a (proper) tank can diagnose this. An ohm test on the stator is not of great value because that would be measured "cold". You could still try the ohm test with the assistance of a hair dryer/heat gun - start heating it up and see if the resistance starts to "significantly" increase across the high speed leads (indicating a problem).

At least that is where I would start troubleshooting given your observations and considering what you have already done to the motor.

PS - this would have been better off being posted in the general discussion area - not everyone checks this section of the forum which is (here) mostly for identifying models/model year questions.

Thanks for the response. Now that you do say that, I have noticed that when the boat acts up the voltage gauge does drop on the dash down to about 12 volts.