When my Mercarb equipped engine has that problem, it is always hard deposits in the thin ( bottom) ends of the jets on the venturi block. These hard deposits don't come off in any cleaner I've tried and must be removed mechanically. A very thin wire, or better the correct sized numerically...
Personally... I am of the opinion that paying someone to take old parts off of an old bad engine and install them in an "new" short block is foolish,
The savings over a brand new all up crate engine are minimal and you get a real warranty. Many "mechanics" like this because they can sell...
Not knowing the history of your engine in particular, in my experience, I've had to replace the disti cap and rotor at least every other season. Spark plugs and wires, far less frequently. As a matter or habit, I never leave the slip until my engine is up to operating temp for safety...
I have seen many posts where it appears as if the poster came into possession of what I call a "Boat Show Special". This is what I call
a boat that was intentionally built with an undersized engine in order to get a low sticker price.
I have a 23 ft deep V with a 5.7 260 HP. It could...
Will need to change the drive itself as well... 6 cylinder engines and 8 cylinder engines use different reduction ratios. The ratio is controlled by the gears in the lower 1/3 of the drive. You may be able to just swap the lower third if you can find the correct ratio The engine should...
Contact Monmouth marine in Brielle NJ. You may be able to save shipping cost by only sending the top third in a USPS big priority box with some padding added..