My Chevy 350 jet boat engine is running lean at the top end. It has a Holley 600 vacuum secondary with 66 primary jets and a metering plate with hole equal to 55 jets. It has a 2.5 power valve and a stiff plain spring on the secondaries. I have never seen a carb with smaller secondary jetting. Is this a normal set-up on a jet boat? I want to drill out the plate to richen it up and eliminate a slight top end bog. The engine is a Marinepower 325 HP, my third one over just 8 years, same original carb. The first two blew head gaskets and ate up the blocks and pistons. I want this vortec to last.