We bought our first small boat for lake fishing a week ago. It is a
used 14' jon boat circa 1981 (according to the license). It had on it
a 40 HP MERCURY engine with serial number 5991890. (With electric
start).

OK - here is the part where you can call us stupid. My first guess
(we didn't ask but should of - excitement of buying a boat that we
could use with out boys - ages 12 and 7 - you know) was that it was a 2
cycle. My wife insisted she saw on the sign that it was a 4-cycle. Of
course, had I bothered to look for a oil reservoir, I guess I would
have had my answer. However, not wanting to doubt my wife (long story
there) I took it on faith that it was a 4 cycle and we put premium gas
into the fuel tank with no oil added.

We took it out on a lake, and it started easily, but then ran rougher
and rougher until it would no longer start (for awhile it would work in
the idle mode, but the engine would cycle up in speed and then back
down, and then eventually die out each time). We played with it for
about 30 min then gave up. We brought it in by trolling motor and got
it back home.

Figured out at that point it was a two-cycle, so I added the
pre-requisite 50:1 ratio of two cycle engine oil (by the way, I just
used generic two-cycle engine oil, is there any difference between that
and marine two cycle oil?).

I also changed the spark plugs and the little in-line fuel filter.
The top spark plug was charred.

We got it to another lake the next day. Put it in the water and
attempted to start the motor. It cranked fine but never turned over
and started.... almost like it is not getting any gas, but maybe it's
not just getting a spark - because maybe one of the spark plug wires is
bad? The latter supposition is doubtful because it did run on Sat, but
not on Sunday - although maybe I broke a wire when I replaced the plugs
I'll take an Ohm meter to them this weekend to make sure they are
good, and try cleaning them up a bit to make sure they are making goog
contact. I also plan on taking the spark plugs back out to see if
there is anything else I can do to clean out the regions they plug in
to. Does it still sound like I have a fuel problem?

I'd appreciate any helpful suggestions.