New Jersey usually gets two weeks of extreme heat and extreme cold (by NJ standards) each year. Here at the shore that translates to about 5-7 days of whole house air conditioning per year. Obviously, the heat needs to be used from Nov until Mar/April.
I looked up the plug wires from a '75 Merc 20. https://www.crowleymarine.com/mercury/oem-parts/outboard/1975/1200205/flywheel-ignition-coil-stator-and-switch-box-group-no-15?ref=28
parts for a '71 were not listed.
Those plug wires look to be push in to the coil, with spark plug boots and...
So the old Merc manual says no multi vis oil, and you plan to use 15W40 multivis oil? It may even protect your motor, who knows?
Gee, how about you visit a MerCruiser dealer or order the correct stuff from Amazon or someplace
Force was bought by Merc, and had Merc gearcases and electronics, at least. Any idea if the valve body is Merc or Chrysler? Crowleymarine has parts lists for both chrysler and force.
If the QS 25W-40 is NA, you can use SAE 30 detergent motor oil, for moderate climates. You also might look at the OEM recommendations, as there are a lot of FC-W motor oils (used in 4 cycle outboard motors) in my local Wallyworld that might be recommended.
I never thought "Trying an oil", vs...
CDI Electronics might have a troubleshooting guide for your ign system Make sure it is for your year as stuff changed in the first years of the V6. Earlier models had 9A rectifier systems and later ones had 40A VR systems. After that Merc went to twin 20A VR systems. I expect the stators...
My neighbor's mercruiser PS cooler rotted out and leaked all the fluid overboard. The boat was impossible to turn at cruise speed. We had go to idle to turn the wheel.
A Factory service manual might be the way to go. Although the ADI ign systems on the V6 engines are common from 1978 to the late 90's, the charging systems changed a couple of times, as did the stators.
Gee, I always liked my OMS system. You get a fresh gas-oil mix all the time. The motor always idles and runs smooth.
I replaced the OMS pump last year, since I thought it was leaking. The pump was 28 years old. it turned out to be a leaking oring on the fuel out nipple. For .05 I could...
Two cycle motors can run backwards pretty well. Set the top piston to top dead center using a screwdriver (or piston stop tool) and see where the timing marks align. I think you should get a factory service manual, as most shops will not want to work on that old of a motor.