EVINRUDE 9.9 - Doesn't run great all the time - '76

[sledneck22]

My 9.9 has me scratching my head. Here's the problem.
So I drive across the lake, wide open, the motor runs great. I get to the other side, go to the bathroom, (wasn't going to crap in a bucket) come back and it takes 20 pulls to start the motor. Then taking off, it acts like it is running on one cylinder sputtering but still moving the boat just not very fast.
It seems like it is flooding out. I have new plugs in it. And after letting it sit for a prolonged period of time without running, it starts and runs just fine.
Is this something as simple as an adjustment screw on the carb or maybe the seafoam in my gas or did I accidentally add too much oil? One of the coils breaking down from the heat and after cooling it returns to normal operating temp? I haven't tried swapping out the plug wires yet when it starts acting up but that's the next thing to try.
I have new gas, oil, 2 caps of seafoam, new gas tank, new gas line fittings. It doesn't leak a drop between the tank and engine.
Thoughts?
Suggestions?
What to try or look for?
Thanks,
Kyle

 

[OptsyEagle]

It sounds like your problem is intermittent, which is always the toughest to diagnose. I would probably want to do an external spark test with an air gap tester set at around 3/8" to see if both cylinders are firing. A compression test would also be useful information if you have a tester available.
I would also want to do a cylinder drop test. To do that start up the motor and let it warm up. Put it to a fast idle and with a pair of insulated pliers pull one spark plug boot at a time. The motor should be able to run on one cylinder so if it dies when a plug boot is pulled you will know that the other cylinder was never firing or is very weak. If it passes both of those test, then keep the insulated pliers in the boat and try it the next time you experience a problem.
Now if it is intermittent it very well could be a coil so if a cylinder is dropping, switch the spark plug boots to the opposite spark plugs and switch the clips that come out from under the flywheel. Start it back up and do the drop test again. If the problem switches to the other cylinder, you know you have a bad coil. If it stays with the same cylinder you know you have a problem, we just don't know exactly what is causing it yet, but we are very close.