Motor was running fine above 3500 and now it's not.
There is no backfiring it just won't go any faster
Don't see it being the fuel pump, if it was the motor would start to back fire from running lean.
I would do this as Scott mentioned
Yes you can do that, but don't use the little maintenance chargers to recharge the 2 Bats. Need to have a charger that puts out enough amps to recharge the Bat it the amount of time you allow
Internal parts are the same "IF" you get a truck motor and not a car.
Fuel pump and carb must be marine
Brass or stainless freeze plugs and and marine head gasket (not auto type)
Ignition must be marine except for coil
Guy might be a reputable rebuilder but should not be selling MPI's with the wrong ECM. Having the wrong fuel tables loaded will not produce the power it should and can damage the motor.
He sold you a new motor and it might cost another $2500
Kind of wonder if it's actually a 383 with correct...
Don't know your boat, but the actual horn is normally under the rub rail, near bow on starboard side. There will just be a grid of some sort covering it. Normally cheap horn and not to loud but meets minimum spec
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Have never seen instructions for any boat of how to remove the gas tank. I've done it but in most all cases it all comes down to cutting the deck to gain access.
With vent clear and bulb collapsing, I would remove the pickup tube and see if it's clear
Depends on your state but it's my understanding so long as the gross is under 26K no one says anything. Even the commercials have a disclaimer listing (for the most part) it can pull above 26K but can be used yada yada
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Looks to me it's Tee'd into another line. Zoom in on middle pic in link
https://www.ebay.com/itm/175847757976?epid=11019384152&hash=item28f157d898:g:DZsAAOSwKLtkruOs
If the elbow is cracked there the water will not enter the motor
Don't see an issue with the other gasket area because it seems to just be layers and gasket just separated when removed
my opinion
Most gauges are not accurate, in case yours was it may have caused an issue, time will tell
You could let it go or dive in further and find out
140 to 120 is not great but not terrible
