( I want to build a shallow-water drive for a canoe. A small outboard
dosen't work well -- been there, done that.)
If you google "homemade mudmotor" on about the third page you'll find a
bunch of posts on this subject ( boatdesign.net/fourms/... ). According
to the posts this has been done successfully and unsuccessfully with
2-strokes -- depends on how it's done. But nothing is mentioned about
4-strokes. I've posted a question there but no results yet.
I would think the orientation of the power head would be about the same
for the mudmotor application versus weed trimmer. One possible problem
with a 2-stroke: Exhaust "tuning" can be critical and if you try to quiet
them with an additional muffler I'm not sure what it would do to the
perfomance.