Check fuel pressure
Check advance at 3000 RPM. Sould be a 20 degree advance all in by 2800
Reving in neutral means nothing. The motor will rev to 5000 RPM running on 2 cylinders with a gummed up carb
However a carb with fuel delivery issues won't rev under load
Could have been a 2-barrel
Holley was used on the higher HP motors thru the 80s. IE, the 260hp 5.7 motor got the Q-jets, the 271, 290 and 310hp motors got the Holleys
The 205hp 5.0 was Q-jets where the 230hp was Holley
you need to follow the factory manual.
you probably wont find anyone willing to work on anything OMC
@Lou C has a write-up on adjusting. you do need the tools.
your local radiator shop is usually looking for work, and they weld aluminum cheap. my guy had more boats and boat parts than radiators the last time I was there.
You are confusing ignition timing and cam timing
Yes, retarding the cam timing will move the power band lower (sooner) providing a bit more torque on the low end
you have to do some troubleshooting to see what needs to be repaired.
either the piston seals need replacing, or there is dirt in the hydraulic pump holding a load holding check valve open.
throw the clymer manual out as there is more wrong information than correct in there. they make bad toilet paper and worse manuals.
do you have Volvo Penta motor and drive, or Mercruiser?
if Volvo Penta, go here for factory manuals...