Come on dudes ... adjusting the valves can't possibly make the engine blow smoke ...
If he's had the head off , he's most likely left something out (rubber o-ring on the oil gallery if it's a Honda type YX150) ... or damaged the head gasket ...
If he's had the cylinder off and replaced the rings ... then he could possibly have the ring gap staggering wrong as in all the gaps lined up with each other ... or he could have stretched the rings too much when placing them on the piston effectively "egg" shaping them ...
Overheating a new motor by letting it idle too long , over revving it , not allowing it to cool after short bed in runs , or running too lean jetting can cause the rings to over expand and that in turn causes the ring ends to butt together ... the now over sized rings push hard on the bore wall squeegying out the oil , which in turn scuffs the bore and wears the rings ... After the motor cools off ... the rings no longer seal ... so your 4 stroker blows smoke worse than a 2 smoker ...
The only other scenario is a valve head has windowed the piston crown ... but the engine most likely wouldn't run in that case ...
If the valve stem oil seals are bad the engine usually puffs smoke on start up and puffs some out when you hit the throttle or back off in gear and engine brake ... but it diminishes as the engine is revved ...
Stuffed rings smoke on start up and get worse as the revs are increased ...