What does everybody run when come to fuel that you run in your boats?  I only use 87 unleaded.  I have heard that if you run premium (i.e. 91 octane) it can actually hurt the motor by gumming up the plugs and other things.  I always though it would be better to use premium.  I am just wondering what your experiences are with using premium gas.  Also does it add any power or is it just an extra waste of money?  

U should run the what the manufactor recommends. As for gumming up plugs, I wouldn't go that far but you do get reduced peformance and more carbon buildup. The compression, bore diameter and a few other things detemine the octane rating and the engineers have already done their homework and told you what's best. The higher the octane, the slower the burn rate of the fuel. Running high octane fuel in a low octane motor does not let the fuel fully burn before it reaches the end of the power stroke letting the unburned go straight out the exhaust. This also lowers combustion chamber tempratures. Since piston dome temps are what keeps the carbon burned off, lower temps mean more carbon buildup. As carbon builds and the motor is not on a reqular decarb program, small bits of the carbon start for flake off. Pure carbon is pretty dang hard, lot more so than the piston and cylinder walls, so it eats away at them. The carbon also builds up in the ring groves, binding the rings and creating more blowby, even further reducing performace. Over time you end up with a motor that's worn out in about half the time a motor run with proper octane and on a regular decarb program.

So, while being very proud of you're motor and thinking you're just taking the absolute best care of it you can, running the best fuel (premium) when it calls for 87 octane, you're actually doing just the opposite.

Thanks for the great response!  That really cleared things up for me!  

87 octane        and merc quikleen on every fill up