Re: carb adjustment Merc 500 (50HP) 1972,
only thing that is adjustable are the idle jets (assuming same as my 1973 500). You can access them with a long screwdriver through the front after you take the face plate off. Hard to find though unless you remove the wraparound and look from the port side. You need to be warmed up and in forward when adjusting (just under load, idling in forward, not screaming across the lake). Typically, you simply close it until it starts to stumble, then open it until it starts to stumble and set it in the middle of those. 1.5 turns out from LIGHTLY seated is good starting point. You can also change the main jets based on altitude but reports of that effect are mixed. It can be done without removing the carbs. To adjust the timing and throttle pick up, search for "Link & sync".
