Quick Update,

We through all the connections from the batteries, bus bars, engine, barrel connectors, and up to the ignition switch. All tight and complete, no corrosion. One thing I did notice is the the Port Engine is slower cranking than the Startboard engine which I will diving into next but that got me thinking about SB's comments regarding the Perko switch, I am going to pull that apart and see how it is wired. Luckily I have the complete red book to guide me. Many of my past Formulas, you could use the trim switches with the keys and the batteries OFF, but this one - the keys and the battery need to be ON for functionality. I also ran through the fuel lines and carbs, everything was clean. The last check is the fuel vent and siphon valves.

Really great having all that information available, isn't it?

My electrical system works just the same. I need power on for the trailer functions to work, and ignition powered on to operate the individual trim circuits.

well, the issue switched back to the starboard engine. Only issue that I have noticed outside of the stumble is that the port engine is slower to crank, my cockpit speakers have become really distorted and all the gauges dip when I hit the trim switches while underway. Looks like I’m chasing a lose connection. The only thing I haven’t checked is inside of the Perko switch. I’ll be digging into it tomorrow.

Perko switches do go bad. Most of the time they are riveted together. Just replaced on last week.

https://www.crowleymarine.com/mercury-outboard/949.cfm

I buy from Crowley all the time never thought to look there, thanks man!

I just refreshed 2 Merc 420's for my Panther. I did change from the stock flat tappet cams to HR 500 EFI cams. I should be able to give some feedback on performance differences compared to the stock Merc 420's in a week or so.
https://www.jegs.com/i/Crane-Cams/271/169621/10002/-1

please start a thread for that, I will be able to contribute in a few months once my engines are together, would be good to have some recent 420 rebuild with currently available tech and parts, not much out there that I can find...

Still battling this issue, stumble/stall still switching from port to starboard every other weekend (aka whenever it wants). Yesterday, took it out on the river and ran strong for 35 mins, parked at a beach so my son could swim for about an hour and then left to head back to the ramp and a few minutes after getting on plane, stumbled again. Shut down engines - removed carb bowl - bone dry. Restarted, removed plug on the side of the bowl - fuel level normal - ran fine the rest of the day.

Today, removed both anti-siphon valves - replaced with hose barb and will test tomorrow while I wait for replacements.

Fun new issue - keys both in OFF - turn on Panel Lights Switch - Panel lights illuminate AND my gas Gauge comes on and reads half tank. Feel good to be back in the boating game......

We talked about the fuel gauge thing... no clue there. Ground Issues causing a funky draw?

On the fuel issue... considering it’s been with both engines, I think maybe some kind of a an issue with the tank vent and/or anti-siphon valves.

It’ll be interesting to see differences since removing them.

At least you’re not into the engines...