bck

You mentioned in the beginning you checked the plug wires with a timing light. Is that the only thing you've done with them? Still using the same wires on the same side or have you replaced them?

C1000

Tell us a little about the latest rebuild, did you use the same cams, timing chains, did you degree the cams etc. Forgive me if you posted this and I didn't see it. when you fie the motors does the Starboard fire right up with attitude and authority, while the port fires up weak and blubbery? Even though the vacuum readings are good and equal, to me it sounds like valve timing is off from engine to engine. But your test results disprove that. I would look a little deeper in that direction. Many things effect valve timing, push rod deflection, rocker arm geometry and ratio timing chain stretch, etc, etc,

Eliminated572

Bck- Plug wires were swapped on the water last engines along with caps/rotors. I was just using the timing light on each wire to confirm each cylinder was getting fire ignition wise.

C1000- complete rebuilds. New cams by marine kinetics. Heads all sent up to JimV for his port work. All new isky springs, isky EZ roll solid lifters, T&D spring oiler rockers, pushrods, diamond pistons, rods, polished cranks, machining/balancing. Jesel belt drives. New belts installed. Both new engines were then dyno'd before rigged in boat. After tuning (jetting ended up very close within one jet size to achieve 12.5:1 AFR average) They were within 6hp of each other. Both fire over on a dime just like last time. Both 34 degrees locked timing. Both same vac readings. Both same lash. Both same compression numbers. Both have completely new msd ignitions. Everything is checking over in identical side to side fashion just like the last engines. Port just seems to rev slower and definitely lacks rpm and pulling power compared to starboard.

C1000

Ok well that answers that, was just a theory, I'm lost now, can't offer anything more at this point! I'm very curious now.

Have you talked to Marine Kinetics, about it at all?

Eliminated572

No I have not. I may see if he has any ideas but the engines both performed as intended until the port side touched the boat and the listed of things to check are checked and crossed off fairly thoroughly. Good thought maybe I will give him a call anyhow.

ICDEDPPL

If it was me I`d adjust the throttle linkages to even out the rpm, wouldn`t be the first time i had the wife drive while I was in the bilge adjusting the same issue.

sutphen 30

have you swapped drives?

Eliminated572

I tried adjusting the cables.
To have even during cruise will drive you even more crazy everywhere else. Inch of slack in one and tight as a guitar string on other. Really pissed me off while docking. I swapped the drives this past weekend when I had them off. Hopefully tomorrow I will be testing again. The problems been here since before the drives were rebuilt last year but worth a shot.

brian41

We recently rigged a 3600 Nor-tech Supercat with Arneson drives and had the same issue. Engines within 1 HP of each other and port down by 400 RPM's throughout the RPM range. First thing I noticed was the port rooster tail was lower than the starboard side so I raised that drive by 1 notch on the indicator and RPM's came in line. After taking the boat back to the shop I put a digital angle gauge on both side of the boat and found the port side of the transom had 1 degree more down angle than the starboard. I adjusted the indicator cables to match the results found and all is well. Might not be your issue but at this point what have you got to lose.

Eliminated572

Thank Brian I will double check. I have been running the port side a 1/2 # higher on indicator but even with that is the 500 difference at WOT. The port ends up to the point of trim just before blow out is how I set them for WOT runs. But anything is worth checking at this point. To get the RPMs the same I would need to awkwardly offset the trim, basically roosting the port and running the starboard flat. I did check the thru hull pick up locations and both are exactly in the same location in relation to the hull and drives. Nothing is screaming at me there either.

Something I did notice, not sure if its any clue. When steering to the right the port side comes unhooked. When steering to the left the starboard comes unhooked. I believe this is very common with cats. BUT when steering to the right and unhooking the port I'll gain about 8 mph. When steering to the left and unhooking the starboard I'll only gain 2-4mph. This is cruising at 40-50 mph. Possibly because im throwing more throttle at the port and its dragged down until it unhooks? Not sure but something I noticed that was odd.....