All new ignitions installed last month. MSD 6M-2L's, HV2 coils, pro billet dizzys. I pulled the chips on last engines and ignition systems 2 years ago and ruled that out. They were ran on dyno with my old ignition systems. But this issue is two years (or more) old and the exact same problem was on the old port engine. I believe it's something common with boat. Vacuum readings and comp check numbers are identical between these engines just like the old ones.

Not sure how to copy the link , thread started by Payton on 3 ,21, 15 fiter separator housing.

About the separator issue? I believe I searched and read that. I will look over again thanks. Mine are Teague separator housings. Look like 3/8" inlets/outlets. I also was able to put my phone over the bulkhead and take a picture of top of tank. I don't see any anti siphon valves. The supply and return are right next to each other on top of tank toward rear.

the starboard engine has exact same setup

if they are 3/8",thats too small for a warmed over 572.

The size is -8. OD of tube on the AN fitting is 1/2". Takes 7/8" wrench. The starboard is happy with it. The issue is existing at all rpm's and loads. Off idle to WOT. Same exact rpm difference the 600hp engines had vs the new 750hp engines. I'm not pointing my finger at that yet.

The fittings on the Teague separator housings appear to be 3/4"NPT.

I hate to say it .... Pull Them ... and Swap side to side . I would look at a voltage drop or a ground potential problem on that side . MSD is notorious for ground leakage causeing issues.

any chance to swap fuel supply lines side to side? feed port engine from starboard line & vice versa?

I am going to try running port side from a 5 gallon gas can along with widebands next test out. I wish someone in St. Louis area had a prop shaft dyno