[Putershark]

Couple of things...

• No matter which type or brand of oil you use, you need to "always" make sure the oil to fuel mixture is correct, period... Even running too much of any high grade oil can foul out the plugs and even faster if you do a lot of idling / trolling.
• Unlike a 4 stroke engine that you can (though I would not) run a lower grade of oil in and just change it more often... You do not have such slack with a 2 stroke engine. It burns it's lube oil and as such, needs a oil that will lube and cool as well as burn off, this without leaving behind a lot of deposits... As I have always said, if you cannot afford the oil, then you cannot afford the engine This for using high quality lubes and fuel is the cheapest insurance policy you will ever buy and much less expensive than any blown power head.
• I would go with the most cost effective high grade oil you can run (I prefer Synthetic) with the highest level if detergent fuels you can find in your area. Just like the Fram Ads say "you can pay a little now, or a lot later" still holds very true.
• You do not though need to run just Evinrude oil to prevent such fowling from taking place. I would also make sure that that spark plugs are of the correct heat range for that engine AND that the engine thermostats are in working condition. If not, the engine can and will run either too hot or too cold for the design intent.
• I suspect that this engine has a carb, and I would make sure that you keep the carb clean using some spray throttle body cleaner. I say throttle body cleaner since it will not strip off any metal coatings (clear coats) that the factory may have used / sprayed inside the carb intake. Many harsh carb cleaners will strip off and remove such (carb cleaners can slowly destroy fuel injected throttle bodies if used) so by using a throttle body spray cleaner, you will still get it clean along with any air bleed jets that may get clogged, without such long term worries... Having the carb intake or air bleed jets get dirty though, can cause the engine to "load up" on fuel at idle and dump in more fuel than needed much like it was running with the choke on all the time. That will also cause the spark plugs to foul out very quickly.