Re: What are my chances?
well, you can't really assume, as you put it, that the lower unit is in working order, in fact should assume that it will be one of the first things you will want to work on (water pump). I think you probably mean that the thing seems to shift OK and is intact and not all bashed up -- all stuff you would want to notice in deciding whether to buy (and for what price). I probably differ from the more technical approach from some of the other listers. When I'm looking at a motor, say, in the $100 to $300 range that I would really like (I do mainly the mid to late fifties magneto types), I will typically make sure that it's not stuck, and in checking that will see if I can feel compression -- can see if there is a compression "bounce" if you have the access to the flywheel. I also figure I'm going to spend about $125 give or take to get the magneto and water pump in shape, just as a given. These are older motors than I think you are looking at in the 9.9-15 hp range (see kfa's post, above). I'm usually pleasantly surprised when I have it in my workshop (with the compression tester, spark tester, flywheel puller, favorite wrenches, etc.) The motors I'm usually looking at are not in locations that provide a lot of testing space -- usually looking at some basics, with the idea that, worst case, I end up with some more OMC parts for my $200. By the way, I never tried that finger-over-the-sparkhole test for compression, but will reserve that one for the next discovery, if I can get at it enough to get the plugs out, have somebody to pull the starter rope, or whatever else figures in. It really is all good fun.