as indicated above, you have a bad connection somewhere between the battery and the motor. check both positive and ground cables, starter connections, etc. clean every connection shiny enough your mother-in-law would eat off them. when you think you cleaned them enough, clean them some more...
all parts for the no longer supported yamaha drive are either obsolete or expensive.
hopefully this nearly 30 year old boat is a family heirloom with sentimental attachment and not a recent purchase.
without knowing diameter and length, spline info, etc you are on your own for a cross to jabso...
your accelerator circuit in your carb is plugged
the pop could be a lean sneeze (go back to the carb), or improper timing
there is no mechanic in a can. however snake oil does come in a can.
so........ pull the carb apart and soak the pieces in carb cleaner and chase every passage with a...
your chap has a fiberglass deck with carpet over it. most boats with carpet do
only aluminum boats and wooden boat ever had bare wood decks
if your deck is soft, it rotted from underneath. that means your transom and stringers are shot and the flotation foam is waterlogged
spark knock can be from many things
high operating temperature (180 is high)
quality of fuel (check contents of your fuel filter)
lack of fuel flow to the engine (AS valve/ plugged fuel pump, etc causing it to running lean)
carb gunked up
Carbon deposits in the combustion chambers
improper...
pull the drive
pull the motor
remove the interior
build a cradle
pull the cap
wear a tyvek suit
fire up the saws
start by reading the 4th sticky down, specifically links 14, 15, 18, 2, 3, 4a, and 4b. all the answers you need are in there...
the gear lube recommended in the factory manual is the best for your motor. since you dont say what lower unit you have, I suggest you look up the factory manual and go from there.
not sure what brand of crane you are referring to, however your overall weight is extremely light for an 80 ton...
Free Boats are usually the most expensive boats. however that one doesnt look in too bad of shape. agree with Jim. pick up the phone and call your local AHJ on registration.
flywheel is $79. its a GM truck flywheel for a manual transmission.
I would get a 1996 or newer (vortec heads and roller cam) vs dealing with the 86-87 stuff
you need the retrofit coupler for the new flywheel
nothing about boat mechanics.
its about SBC design generations
you can bolt in any SBC you want. however your motor is 1-piece RMS, so anything 1986 and newer will require a new flywheel.
all SBC's and BBC's from 1956 to today have the same flywheel housing bolt pattern.
your accessories...
so you pulled the drive, verified the gimbal bearing, checked the alignment, inspected the U-joints, changed the fluids, went thru the fuel system, ignition and shift systems as well as all the trailer maintenance?
you need to go thru all the basics before even using the boat. this is all the maintenance that the prior owner didnt do. not to mention your registration, etc. boats loose money daily.
all the information one would need to rebuild a boat is found here: https://forums.iboats.com/threads/how-tos-and-other-great-information.283508/
start by reading links 14, 15, 18, 2, 3, 4a, and 4b in that order in their entirety. watch every video, read every post.
