I hope someone can help me with this. I have a 175 Jackpiner, 1972 , that was in a barn for several years. I did the usual cleanup (renewed carb parts, plug, air cleaner, fluid change etc.). The engine started and ran well for a minute, then progressively more smoke came out the tailpipe and the engine seemed to "load up" or "four stroke". At this point it will barely run with full throttle, with lots of smoke out the back. Any clue as to what I should check?
Crank seals
You may have a clogged exhaust, some little critter may have had a nest in there. You didn't mention the air filter either.
I think you should take Doug's advise first. Check to see it it is breathing properly and check the exhaust. If both are ok. Make sure your fuel mixture is good. With the new oil you don't do a 20:1 ratio, follow the direction on the can/bottle. If all else fails, it is more than likely the crank seals sucking oil from the clutch side.
Donny