rpm's mopar 318's spark plugs

[cthattars]

I purchased in 2005 a 1976 f26 with hard top. The owner before me should have been arrested for having any tools in his hands, any way i have been strugling with the engine rpm's for a couple of years even after a tune up i got free from broker that sold me the boat. the only problem i still had was an rpm issue would not go above 2600 rpm's since i owned mopars as a kid growing up went back to what i know. pulled the sorry a _ _ ngk plugs and put in autolite here's what made the difference is the reach of the plug into the cylinder ngk was 3/8 and the autolite had a 3/4 reach into the cylinder. much cleaner and more even burn of fuel and now i run at 3600 with 14x10 cupped gps speed of 29 and run 4000 14x10 uncupped prop gps speed 30 each with two passes east to west and back. should run better after bottom is redone looks like four coats of touchup paint on bottom, on lake erie rack and launch so going to epoxy bottom, fine someone with a rh prop different pitch or dia to get alittle more out of it. 19 years experience at hatteras yachts. helped in rebuild