mark linger

just received boat back with re-built carb[1993 merc 502 mag motor]at idle at up to 1200 rpm the engine was running rough and smoking.i took boat back to shop and thet adjusted mixture.boat ran fine for about 15 minutes,but when i returned back to marina after short ride,engine started to run rough again.did i get a defective carb or does shop not know how to tweek/adjust??
any ideas

Offshore Addiction

few things to check,you have to make sure something else hasnt contaminated your new carb,make sure your previuos carb hasnt possibly fouled any plugs,make sure your fuel is still hot,(lately our fuel from the pumps here has been going dead within 30 days!).....then do a compression test just to make sure....and if all those pass ther test your back to square one......you got a bad carb.....if you need anything else call me at 813-247-3049 ask for AL