Verdict is in it was the carb! I wasn't able to attend the last sea trial but mechanic reported back that she ran strong and idled proper. He did discover that the tach itself seems to be acting up. I had changed all the gauges but left that one because it reflected the accurate boat hours. I'll check the connections for corrosion and change it out if I must. We had nasty weather yesterday but if it's decent today I'll pick it up and take her for a run.

Ive seen tachs that are actiing up make a motor run poorly but usually on top end at wot fwiw, Smitty

Thats great. I would have bet money you had a gasket leaking vac. Glad it was just carb and hopefully he stood behind it.

yup or tachs without that issue but needle bouncing or stuck that just need the rear dial for cyl # select slowly turned back anf forth to rub clean it’s contacts. Fixed 2 last year this way. And several others over the years.

I woud have thought a man like you,using a rubber mallet and smacking it a few times.

Yes, but that should be in the Pornhub forum, not here.

My first car, a 71 gmc 2wd pu with a 350 , stayed stock for like 48 hrs after I bought it in 1982, 80$ black jack headers, aluminum intake, crower cam, you name it and most of it was USED stuff as I didnt earn alot of money during that recession and was in high school. Well, lo and behold, I was at a rummage sale and found a SUN SUPER 2 chrome tach in a junk pile for 3$, well, after installing it, randomly when I tried to hold that 350 to nascar like RPMS (I was 16 or 17) it would randomly breakup at 5000 or something instead of floating the valves at 6000+, I fiddle fukked with ign, timing, plugs, DWELL on points (YEAH) and it would seem to be "fixed" then come back. Well one time when it was not revving for ****, I tapped on tach. Got my azz zapped, somehow it was shorting ignition out randomly. Unhooked wire from the coil to tach, revved to valve float every time, the good ol days!

Update:. Motor still not running right. In the process we discovered the tach was acting up. I took off trim plate to access back of tach, sprayed some electrical cleaner and rotated the thingamajig and put it back into position which seemed to clean the contacts well and now has tach seemingly Active. No jumping around when tapping on it. Boat runs good up to about 3200 rpm which gets me 30-32 mph (sea ray 260 sundancer so solid numbers for a heavy cruiser). When giving it more throttle I hear motor get a little louder but little additional rpm maybe gets to 3500 and no more speed.

Additional things we have done are as followsBrand new Edelbrock carb, many times rebuilding carbs just doesn't seem to work and a new one is in order. Didn't fix issue, same thing.
Troubleshot fuel delivery, no antisiphon valve at the tank just a hose barb, clear flow. Took out tank pickup it's in great shape.
Replace fuel line from tank to fuel pump and eliminated that small glass fuel filter. That seemed to make idle a bit better as we were having trouble getting idle down to 750, seemed like it was sucking a little air. Once fuel line change was easily able to get idle adjusted down but still nothing on top end.
Swapped out stock fuel pump which was new and replaced with a Holley 110gph higher flow. No change. I think we have ruled out starving for fuel.

Next thing I'm trying is new plug wires, hard to believe but somewhere in all of this engine rebuilding and what not new wires were NOT put on. I believe it was an oversight due to product backorders. Wires were something we wanted oem and couldn't get them and got forgotten about. I just put new wires on and will try sea trialing tomorrow. If that doesn't fix it I believe it's down to 2 things the thunderbolt module not advancing timing or some problem with the valve train. Anyone have any other ideas? I ordered a marine HEI distributor and want to eliminate the thunderbolt 4 but honestly, I don't know if this distributor can. E changed with the engine in the boat. I hope I'm wrong about that

Also should add that we have worked out way through all the old fuel from January of 2021. I have since put in 50 gallons of 93 octane. Not ethanol free but seemed like I should focus on having the higher octane with the engine parameters vs no ethanol. While I understand that low octane fuel can cause problems, it shouldnt prevent the motor from revving past 3500.
FInally, I'm far from an expert but nothing about th motor sounds bad. Idle seems smooth and it runs good up to that 3000 rpm mark then it just won't go. I changed wires today, I suppose I should pull plugs and double check gaps on them too?

What made you or he think it was fixed below?

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