i must have seen about 100 posts where someone starts off asking a
question like 'i was thinking I could save myself some money by turning
a lawn mower (or motorbike, leaf blower etc etc) engine into an
outboard. can it be done'

The discussion goes on and on... with the outcome being something like
that yes you could do it, but it would be silly, unreliable, pollutiong
and probably would save you nothing in the long run anyway.

Here's a pic of one that someone made earlier anyway, just to make the
discussion a bit more interesting next time~

http://cgi.ebay.com.au/ws/eBayISAPI....MEWA%3AIT&rd=1