Briggs and stratton intek 17.0

I have a 17hp intek model number 31f707 e1 that smokes really bad. so far i've put a new head on pulled the piston and checked rings rebuilt the carb checked the crank case vent, done 3 oil changes unhooked all the fuel lines and poured gas directly in the intake. The compresson is 150 psi. A friend gave it to me because the connecting rod broke and he had a small engine shop rebuild it, everything was fine for about a month no smoke or anything after that. then all of a sudden it started smoking . it doesnt smoke at all on start up. just after it has been running for about 5-10 seconds