Re: 1977 evinrude 6 hp fouls out the bottom plug
What JB said.
Also, to answer the specific questions, no the '77 does not have crankcase bleeder valves. And the fuel pump suggestion is a good one, but wrong cylinder. A leaking pump diaphragm will foul the top cylinder.
Consider the possibility of water getting in the cylinder. It doesn't have to be gobs of water either. In addition to the usual head gasket and exhaust cover gaskets, there is a carbon seal on the lower main bearing. That could be broken or messed up, letting water get into the lower crankcase and on into the cylinder.
I wonder what is "any length of time"? When they removed the crankcase drain valves in the name of pollution, motors no longer idled so well for so long as they did in the good old days. For all day trolling, get an older motor. Or a new 4-stroke.
