Rpm issue ideas.... I'm lost....
 

Since building my new engines I only recall seeing equal rpm a handful of times and not at all this season to date, I am gonna list what I have done and my next idea, wondering if I can be missing something ...

My port engine is DOWN 1-200 rpm after 2500, before that they seem equal....

I questioned power all last summer thinking maybe ones that much less HP, so I dynoed them while out for Trans upgrade...

That being said I know for. Fact both engines are nearly identical .3 tq apart and 3 hp apart....air fuels run rocker in boat but equal to each other, showing high 10's to low 11's so I jetted both engines down 2 sizes, starboard runs 11.8-12.2 across the board, port showing much richer 10.8-11.2 all the time.. Questioned hatch airflow ran with hatch open 10" no change at all.. 3" flame arrestors that have pretty much been gutted, I did not try running no arrestors yet but starboard is fine so I don't think that's an issue.

So leads me to think something changed between being on dyno and going into boat, Trans is different then last year, props different, did same thing with my old Trans and also the new one, pressures monitored and are close on both transmissions.
Same drive as always on port, don't see that being the issue since at times it has been equal in the past with the same drive.

I have noticed light electrical issues so I replaced 8 pin connector with a new one, no change, even though engines dyno same I swapped carbs, wires and caps, rotors, verified timing all the way to WOT, fuel pressures good, new plugs, fuel filters... Floats are right..

My next idea is maybe just maybe (I doubt it) but the coil acts up in boat but not on dyno? More get in bilge vs dyno, or the rougher vibrations in the boat or just bouncing on water messes with oil in the coil? I have had could do odd stuff so I have a brand new one for a spare I am swapping out. Another think I was thinking is the engine harness, I think we wired my all in 1 distributors direct to power them and bypassed my harness, so possibly my harness is causing an issue, if the coil don't do anything I plan to run wires direct from ignition switch to distributor bypassing the 8 pin plug and harness...

I guess I am trying to see if I am missing anything... So odd they dyno same but are off in boat and the mph reflects that best I seen this year is 72.1, last year with both at 5500 I saw 73.7, that happened one time rarely see 72-73 now

Besides that the engines run flawless and I logged 50 hours since builds were done, nice to be using bit a lot!

Any ideas are appreciated but I hope I am onto something with coil or harness...mild thunder and I are running out of things to look at lol

This was Friday, 90 degrees and extremely humid, half tank fuel and 69.8 mph

Don't mid the gauges, replacing now with auto meter marines, tachs already done
[ATTACH=CONFIG]558116[/ATTACH]

Air fuels WOT

https://m.youtube.com/watch?v=iurnf_hS8tw

Are the props perfectly matched?

I have had 4 different sets of props no change 2 sets labbed, one set brand new and my 25 pmus's

Also swapped my old tachs side to side, and also have new ones, but the speed also reflects loss of rpm.

kust throwing things out.... both carbs open the same?

This is what I want is extra ideas, but yes checked that, seems to accelerate equal till 2500 or so the port seems to lag.

Both motors have power steering pumps?? Doubt they make that much drag but....

hydraulic roller lifters correct. What kind? What are you using for ignition? Did you try swapping those out. Otherwise throw a simple HEI on the engine down on rpm. Also did you dyno engines with your ignitions your currently using. I only ask cause some dynos are set up to use their own. Oil looks same in both engines. Cut open filter on down rpm engine. I'm just throwing that out there. Sure it's fine but rule it out anyway. Drives feel good and spin the same after warmed up in neutral on trailer.

If you ruled out pretty much all the above maybe reset valve lash.