Run what's recommended by Mercury ... and ... a lotta people think the
higher the octane the better the performance ... not true. Higher octane has
a higher flashpoint which essentially means it doesn't burn as good as lower
octane ... which means it doesn't pre ignite in a higher compression engine.
And a lotta car engines have a knock sensor to adjust the timing in the case
of preignition. A buddy at work says he buys high octane all the time, big
grin on his face ... I said why, we talked ... he says ... hmmm ... think
I'll switch to the recommended lower octane ... and save a lotta money. Even
my subaru at 10:1 or so compression can accomodate low octane.

"Dave Molta" wrote in message
...
I'll be running a new rig this year, a Lund Fisherman 1800 with a Mercury
114 4-stroke. I'm curious about whether I should run 87 or 89 octane. My
old Yamaha 2-stroke ran much better with 89. On the other hand, I've never
noticed a significant difference on 4-stroke motors in my cars.

Any input?

Thanks,

dm