1975 ford 233hp not acheiving full power

"hello, I have a 1975 ford 351

"hello, I have a 1975 ford 351W 233 hp mercruiser. Had a rough idle and adjusted the idle mixture screws, ran full can of carb cleaner in carb. Replace plugs, gaped points to spec and checked with dwell meter and adjusted to 29 degrees for dwell. Finially adjusted timing to 10 degres btdc per specs. Vacume gauge reading is 15-16 at idle. Runs smooth, but under load still lacking power and slight backfire. Any ideas? every gauge is normal. Replaced fuel filter in carb and tank- carb gets plenty of gas. One other question, dwell/tack meter reads a idle rpm of 600 which compares to boat gauge, however when i increase rpm to 1000 or above, boat gauge is a lot higher than the dwell/tack meter, is the boat gauge faulty? Any ideas welcome, thanks, Tim"

"Plug wires failing under load

"Plug wires failing under load,dirty main jets?"

15-16 pds for the vacuum sound

15-16 pds for the vacuum sounds a little low. Is the gauge steady or fluctuating? Maybe a vacuum leak? Is the timing advancing? Maybe the weights on the advance are frozen. I would check compression also. Good luck.