Re: too much throttle kills motor...
Since the early 90's outboards have been designed to run on E-10, I live in one of the first states that required it, so for 20 plus years everything I own has been on a steady diet of it. Some of the very old motors do have some issues, that is until those parts are replaced with newer rebuild kits (these need to be good quality kits or you're right back in the same place). How do cars run on it for decades and have no issues with premature failure of rubber parts? (yes, I know the fuel systems can be different, but they all use rubber parts.)
Most of the small engines that have problems with it are made with junk fuel lines (made in XXXXX) and other rubber parts that should never be used around any type of fuel, so there is a reason for these failures.
The thought of E-10 related fuel issues never crosses my mind, and hasn't for a very long time, nor does it come up in conversations with other boaters around here. The more recent the transition to E-10 in a location the more horror stories you hear, and there is a reason for it, but E-10 is not the evil monster it's made out to be. Is it great stuff...no...is it the cause of every motor related problem that exists...no.
In some situations it can cause problems, I know this, but for 99% of the boaters on this site the real problems aren't something they run into.
Your 84 Merc "will" run better on E-0, it has more BTU's, so it will make more power.
