If you infrared the cylinders to see if there is a temp difference on the exhaust manifolds that could tell you if you have a cylinder issue?

Have your local Mercury dealer use G3 and do a drop cylinder test. EFI engines are incredibly good at seemingly running OK on 7 cylinders. We had a client with a 38ZR w 700s who had no idea one coil had failed. Needs to be done in the water (even if still on the trailer) in gear around 1500rpm.

I plan to do that exact test in the next few days. Doesn’t matter whether it’s under load or not? It seems to idle fine, but I was thinking about at least put it in gear for a minute or two under some load to see if that if I can tell a difference between the temperatures on the runners.

I have a good boost, equal on both side on both engines

When was the last time you replaced your in-line fuel filters? They are small and flow a lot. Easy to get clogged. How about Fuel/water filters? Mercury had a recent bad batch of these.

I think i may have found the problem. looks like somewhere along the way the throttles got misadjusted and one doesnt engage the throttle body until about 2 inches after the other. Will adjust this week and see if that does it.

Sometimes its the simplest thing....

Thanks to all for the great suggestions as always!

FYI, adjusted the throttle linkages and now both motors run consistent rpm and have similar boost profiles. Thank to all for the great suggestions, sorry to waste your time on something so simple, but i am VERY happy that this was all that was wrong!