TOPIC: 1974 Mercury 500 50 hp Stalling issue help please

I have a 1974 Mercury 500 50hp that has a stalling issue. The motor starts and idles fine but will stall out when put in gear either forward or reverse. It will keep running if I tap the choke button when it is about to die. What has been fixed already and checked; Compression is between 120 and 119 psi. in all 4 cylinders, Spark is good, the internal wiring harness was replaced because of corroded wires, new spark plugs, carbs rebuilt, new fuel lines and tank, fuel pump rebuilt. Any help on this issue I would really appreciate it.

Sounds too lean; have you tried adjusting the idle mixture screws?

Just for a rough setting, turn each needle in (clockwise) until it lightly seats, then turn out (CCW) about 2 turns.

This may be a bit on the rich side but if you have been running too lean, you'll definitely notice a difference. Very common issue on these and the big Sixes, you need to tweak the carbs in the water, in gear, engine fully warmed, for the most accurate setting.

Generally you adjust for best idle (in the water), as lean as you can adjust (to get a clean idle), while still being rich enough for smooth acceleration. A bog off-idle is almost sure indication of too-lean idle mixture, when everything else is already up-to-snuff.

Most old Mercs are gonna want to run a bit on the rich, "lumpy idle" side.

HTH..........ed

Thank you, I will let you know how that goes. I will give it a try as soon as possible.