Bozeman Bob

Pretty much goes with the territory , I guess if it bothers you that much ,don't go out until the hatch's [ these are not as bad as the biting flys ] are over with

If fluid is up to the vent cap I would check solenoids. I believe there are two, one for up and one for down . Might even try swapping them to verify.. Cheap enough to replace , car parts store will have them ,not marine specific. If the unit is somehow bad I think I have one ,let me know. ( have a lot of spare parts from over the years out in garage )

Yes

Since no one has replied I will ask the obvious . Wood ,aluminum , fiberglass ,condition , any time frame and type .length of boat ? A few more details may or may not help.

Most of the tournaments have eliminated using a observer this season.

In most cases ,not all , the engines are over propped a bit ,so adding a little hp isn't going to mean buying props , just puts it on the money. May even see a little higher cruise speed and better mpg. What's your max rated rpms and what are you hitting at WOT ? Time not a factor ,go local and ask the builder for recomendations on things like roller rockers vs stock and heads will have to be shaved ,so he should / will make sure you have enough stock left for that to happen. Good luck !

They have not made the 3i8s since the late 80s ,so I don't think your going to buy a new one. ,especially 2 for 3600. Unless there short blocks which is a route I would not take. More like 3600 per engine ,longblock and rebuilt not " new " and maybe with a 2 year warranty, depending on who you buy it from. Personally I prefer having someone I know rebuild them . That way I know what was replaced ,what options I might have for any upgrades in durability and possible HP. Buying online means you don't know for sure if oil pump , intake valves , lifter springs ,water pump ect have been replaced or they were in mfg specs and not replaced. If your in a hurry you may have to buy online since this is the busy season for most rebuild shops. I would ask and make sure the engine was put on a dyno to be broken in and checked for any oil ,water leaks before I dropped it back in the boat. Going from.a 2 to 4 barrel carb with a better tuned intake manifold may give you a extra 20-25 hours per engine .

12 volt test light and start tracing from the switch back if no power at the switch. Switch forward if you have power there. Can't really tell from the wording in your post what exactly isn't getting power. Check all grounds as well , pretty basic .

Better off grounding it to the engine block ,or wherever your main battery is grounded to. I had a Cannon rigger that would not self stop at the waterline because the battery wasn't correctly grounded, worked fine after I did that.

They (NAPA ,any auto parts store ) do sell 12 volt 10 ,20 , 30 amp circuit breakers that have spade terminals on them. Much easier to reset than replacing fuses ,some are auto reset as well.

OP just stated the sending units were different

I would get a infra red with laser light and compare the two engines over varying speeds. Had a burning smell we couldn't figure out , turned out to be the rubber hose coming off the exhaust manifold. The Temp gauge was always ok because it ran off the top of the intake manifold which was part of the closed cooling system. The exhaust was not part of that reading and the raw water elbow going into the manifold was blocked up with crud , the heat gun showed it.