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Hi Lance, sounds like you may have a bad cylinder or two. Usually when a engine has sat we look at the fuel system. However your losing 1300 rpm and then coming and going make me suspect the ignition.
If you have or can get a timing light then we can use it to diagnose the engine.
Put your timing light on the top cylinder, start the engine, look at the flashes from the timing light.
If you have good flashes move the timing light to the next cylinder. Do this for all the cylinders. You can do this with the engine backed into the water still on the trailer. Repeat after 2500 rpm. If you have just one bad cylinder, move the ignition coil on that cylinder to another cylinder, retest. If the problem moves with the coil the coil is bad. If it stays on the same cylinder after the swap, the problem is elsewhere.
Post back your results and we can go from there.
The problem won't be the cylinder itself but the ignition on that cylinder. You could have a coil that is internally broken and when it heats and cools works and then doesn't. Common problem. Using an inductive timing light just allows you to see which cylinders are firing. The problem could be anywhere in the ignition system, which is why we will take it one step at a time.
Ethanol could cause fuel problems. But usually it works or doesn't.
Possibly but not likely. Pull the spark plugs and if they are black, clean or replace them. I would recommend going back to 50 to 1.
If it is a bad coil you will be down on power. This can strain the engine. If the fuel is partially clogged then real damage can occur, You are taking a chance if the engine isn't 100% correct. So I would try to find the problem before any real use.
I'm off now if you have further questions on this I'll respond in the morning, I'm in est here.
If it is running perfect you can run it normally. I would run it very briefly then check the spark plugs, if they have a normal burn, then you should be OK. It is possible you had a little trash in the fuel system that went through. If the acceleration is a little flat, check the firing and don't run the engine wide open.
Let me know what the engine does when you run it.