3/16″ is too small. It should have a bayonet style twist-on connector. These should be easy to find. Each carb has its own, built-in fuel pump; so you’re not missing anything there. When right, those were some of the finest-running two-stroke engines ever built. Like Crosbyman said, though, look for deterioration of wire insulation. That era Mercury was known for that. Connector should look something like this:
Plumbing should look like this:
https://www.marineengine.com/parts/mercury-outboard-parts/500-50/4357640-thru-5531629-usa/carburetor-linkage-and-choke-solenoid
A couple more thoughts: Yours was right around the time Mercury transitioned to stainless steel shafts in the gear case. This would be a good thing, if you have it. I think you do; but it’s close. Also, if the water pump impeller is more than two years old, do not even THINK about launching the boat until that is replaced. The impellers were rubber, attached to a brass hub and that attachment method would fail, without warning, sometimes in as little as two years. Your engine would cook before you had a chance to slow down. Another thought is that, since those engines had no thermostat and four cylinders, they used quite a bit of fuel That would be normal.
Long live American manufacturing!
