sounds definitly like carb issue. most carbs have an idle circuit, the jet can be clogged up by gas turned into gel or a bit of dirt from dirty fuel plugging the port. try soaking the body overnight in acetone, then blow&blow&blow all the jets and holes in the carb body with a 100p.s.i. air gun. you'd be suprised just how stubborn a little obstruction can be! when you're confident you've removed all obstructions, set float hieght & re-assemble, making sure the float bowl gasket is sound, no leaks . while you've got the float out, put it in a glass of water and make sure it floats, no holes in it. if it still won't idle, you've got another issue. often these older outboards have bad coils, that is the insulation on the underbody of the coil has broken down allowing the high voltage spark to short to ground. so, instead of travelling down the high tension lead and firing the plug with full voltage, part of the charge is being grounded out through the hole in the coil insulation to the mounting plate. i've had two outboards with this identical problem. good luck.