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.

Probably one but take belt off just to confirm. They do rob near 15-20 hp I always figured but could be wrong.

No PS on either, I have full hynautic steering, has a pressurized canister for power assist.

Both engines have MSD ready to run dist, my engines were BOTH dynode in full marine trim as they sit in boat, even my Stainless marine exhaust, oil is fine, all is fine and identical on engines like I said they are .3TQ apart and 3 hp apart... I have seen full rpm with this drive, not often but I have, so I don't thin k the drive would vary the rpm..

Not many dyno as they are in the boat like I did..

https://m.youtube.com/watch?v=KqmM7YHqnaE

https://m.youtube.com/watch?v=F5sQmgFHOf4

Swap carbs. Run it and see if it makes a difference. I rebuilt one of my motors a week ago do to Mechanical Advance in MSD not advancing and dropped an exhaust valve. (Distributors are locked now).The motor that dropped the valve was always the stronger of the two. When I rebuilt the motor I went from flat tops to a dished piston. (Getting ready for winter project) lost a full point of compression in the motor. Took it out an ran it this past weekend. Guess what... That motor is still stronger still accelerates harder than the other motor even with full point less compression. I figured the thing was going to be a turd.

I did swap carbs still no change, even though engines are equal in dyno, same day, same temps..

[ATTACH=CONFIG]558120[/ATTACH][ATTACH=CONFIG]558122[/ATTACH]

Did you have any work done to your drives? If so, is it possible that one is set up tighter than the other? Also what about the condition of the running surface in front of each drive, any thru hulls, gouges ect? Any of these could induce air into the prop and cause higher RPM on that engine.

I did do a lower gear on port drive but pretty sure I seen equal rpm since that, we did also verify proper overall resistance in the drive and was well within spec, if it comes down to it I will swap with another left drive I have 3 spares... Even spinning by hand I don't feel it different tben other.

Hull and all that is fine the boat always hit 5500 before nothing changed on hull, water pick ups or any of that.

You guys will see why I am going insane trying to figure it out!

Have you checked your throttle cables/ linkages for equal throw?

Yes I did

Are the drives trimming up equally?

Yes,I have even trimmed all the way in and held WOT just to check still off.

make sure the timing is the same.

I would get the AFR's the same on each engine, weather will play a big difference in the power they make. I'm guessing the leaner one is up on the RPM

They were same last year and also this spring until I jetted down, port still rich starboard is where I want it, when Mild Thunder and I changed jets on dyno we too air fuels from 13.0:1 down to 12.0 and saw a 10 ft lb gain in tq, and lost 1 hp. I agree the air fuel needs evened up but jetting itself does not seem to be the rpm issue, since the rpm was missing when they air fuels were even, I am still leaning to the coil maybe since with less jetting then starboard I still see 10.8-11.2 as of right now ...

This is a very annoying thing because no matter what I have done nothing changes.

I had hatch open and verified while running even, not just revving at dock.

Have you tried moving Ronnie around to a different seat? :)

Hahahahha

Maybe I missed it, but did you try to swap the coils?

Anyway to check Voltage / Amperage of the ignition? Are you sure the ignition is holding up on both sides at WOT?

That's why I suspect coil vibrating in boat and not dyno, or a wiring issue in my harness maybe that we didn't see on dyno, we did not use plug we wires ignition direct to dyno, I checked voltage running at idle, no way to really check under way at WOT... Ten again I can probably wire a volt gauge to ignition for temp use and have someone watch it... Hmmm

I am tonight and test this weekend I never messed with that dice they were same on dyno,!but I am thinking vibration and waves could make it act up and that is not the case on dyno, so yes I was swapping them tonight ..

I meant to touch on same thing earlier and then forgot. is it possible to run both engines off both battery's.

If you've cked everything mentioned as it sounds like you have I would almost have to think its past the engine. Not a water pump or alternator seizing up or any other belt driven accessory? Again just thinking out loud.

Right I really have addressed nearly every possible thing, the coil idea just came to me yesterday, it's really seems to something that shows up when in boat not on dyno, I also dynoed with sea pump and alternator charging and engines still 1 hp apart. Like I said it's been down all last summer and all this year... Really annoying since it wasn't when I first put them in boat I saw full rpm just a few times... The rest it's always lagged over starboard

Has to be a really fukked up issue that's obviously hard to figure out... Ugh

No water pumps, no power steering just alt and sea pumps.

[ATTACH=CONFIG]558130[/ATTACH]

Do you see the RPM difference from the start, or does it gradually show up as you run the motors, heat up, WOT ...

move the beer to the other side of the boat.

Seems ok to 2500 ish then I notice lag

Lolol