I have a 93 Formula 33 foot with twin 502's just recently rebuilt. The boat is not breaking the 40mph barrier @ 5000 rpm. Comes up on plane fairly easy. Port engine jumps from 3500 to 5000 rpm much faster than starboard engine. I was thinking that maybe the engine coupler may be slipping on port engine. Don't smell burning rubber but do feel some vibration with port side. Props are 23 pitch stainless with no visible signs of any damage. Engines are not overheating. Any Ideas?

Something is not correct for sure. You should be running about 60 or so with 23 pitch at 5 grand. What is the condition of your props? Check each blade very carefully for any cracks, flolded over blade, dings..... What kind of prop? If has a changeable hub make sure that is not messed up as well. I doubt it is your coupler as from what I have heard when they go they go. How much are you triming the boat? Are you trimming the same amount? On the motors are they carb or EFI? Have you checked your fuel filters and so on?

Check the hub in prop. If a coupler went it would free wheel. Been there, done that. Make sure you don't have one of the motors missfiring. That can be your vibration. Distributer cap and rotor are very prone to corrosion.

I have removed the prop and see no signs of damage to prop, washer or splines. They are Mirage props. I have not checked fuel filters, but the engine itself does not seem to be missing or any latency. Just HP reaching the prop on the port side.

Do the Mirage props have removable hubs? are they the plastic hubs? Plastic spin much easier than brass. If they spin there won't be any damage to the splines you need to pull the hubs out to inspect for damage.

Removed the distributor cap and everything looks good here. The Mirage props are one piece fixed.

Have you tried pulling back on 1 of the throttles at a time while running to see if the boat losses speed or stays the same? Is the bottom clean, free of algea and slime? That alone will keep a boat from going anywhere till it wears down.

Gotta be easy to diagnose if both motors are hitting 5000 and the props and couplers are good.

If you are hitting 5000 rpm's something is slipping. The rubber inside the prop hub is probably slipping. you visually will not be able to tell more than likely.

Bottom of boat is very clean. Up to about 4,000 rpm, throttle is in same position for both engines. When you push up on both throttle levers at same time the port engine revs up to about 5300 and starboard only to about 4700. So you have to back off the port engine throttle to bring it back to 4700 but does not seem like the boat slows down that much.

BTW, thanks for all the attempts so far.

Port engine jumps from 3500 to 5000 rpm much faster than starboard engine.


Have you checked the engine timing, sounds like maybe the timing on the starboard engine maybe retarded if it seems more sluggish that the port engine???