Re: 1976 evinrude 15 hp not opening up when full throttled...please help!
I wouldn't get ahead of myself. You don't even know what is wrong with it yet. If it were me, I would first do an external spark test to ensure that the ignition can put out a spark that can jump a 3/8" gap, and more importantly that both cylinders are firing. Now if one is not firing (as I suspect), I would switch the clips that go to the coils from under the flywheel. They are just behind the flywheel and easily accessable. Run the spark test again and see if the lost spark is on the same plug boot or now on the other. If it is the same boot then you now know it is a bad coil. If lost spark is now on the other boot then your coils are fine and you have lost spark somewhere up in the flywheel (probably dirty points).
If you are getting good spark on both plugs (jumping 3/8" gap) then fire it back up in a barrel and try pulling (with insulated plyers) one spark plug boot at a time, to verify that it is running on both cylinders. If it is, then look towards your carburetor for the problem, but if it is not (which I suspect) then you most likely have a mechnical problem in one cylinder. Low compression, bad leaf valve, poor crankcase seal, fuel flooding from fuel pump, etc. To verify this, while running pull a plug boot on one cylinder. If it keeps running, put it back on and then pull the other spark plug boot. If the motor dies, when one plug is pulled, it tells you that the other cylinder was the only one working. Since we already tested for good spark, it almost has to be mechanical or carb related. To verify even further, connect up the spark plug boots AND the coil clips to opposite cylinders. Now run the motor and pull each plug boot at a time. If the problem cylinder moves to the other cylinder, then it is ignition related and if it stays on the same cylinder it is probably mechanical in nature or the spark plug itself.
That is what I would do.
I would check the thermostat at least.