Volvo Sx Bogging Down, no plane

[Island Garry]

Hi all. I have a difficult problem that I would appreciate some help on before I haul my boat as I have little qaulity mechanical help on the small island I live on. I have a 1998 33 foot boat with twin 5.7 volvo pentas and sx drives. the props are 15 by 17, stainless and in good shape.

within the past seven months I have tuned up both engines, done drive maintenance (oil and seals), repaired a leaking gas tank and installed new fittings and pickups, new fuel filters (more than once), and rehubbed the rubber insert in my starboard prop. here is the prob --

it began intermittently, I was having trouble getting on a plane from the starboard engine/drive. first it would get up to the 3200 rpm I need to plane in moderate seas and then without warning drop to about 2900 taking me off a plane. then it was fine for a couple of trips. it got to a point where I was throttling the starboard engine higher than the port to maintain the plane. The last trip out, it would first not get on a plane at all, the starboard engine was laboring big time like it could not deliver the power to the prop. it hovered at about 2700-2900 rpm under load. It got on a plane for about a mile, then off the plane. After several attempts I got onto a plane in a large following sea. finally the same prop I rehubbed spun out coming off a large wave. I put on a temporary spare prop I have of much less pitch (not good for planing) and no plane --

the engine runs smooth, sounds good, when the prop spun out reved to 4500 as would be expected, no probs at all at lower rpms and manuevering. Could it be something still limiting the engine under load - what? could it be that the rehubbed prop was "slipping" but not enough to rev the engine high? or is there something in the drive that could cause this? I am not sure what that would be/ Help. Garry.

[USCGRET/E8]

Check the simple first...I have known water in the fuel to do what you are experiencing.

[Island Garry]

I appreciate your thought and have thought of it, but the other engine runs fine and it is one gas tank for both. I also have a water separator in addition to my regular volvo fuel filter, both are fine. I should also mention that I have fuel injectors (throttle body and had a local mechanic replace the small screen filters on them about 9 months ago (not many engine run hours ago, however, as I have not used the boat too much).

[gonzo]

You need to check all systems before spending time and money replacing parts:
Compression, ignition(spark, plugs, cap, rotor), fuel delivery pressure,fuel pickup vacuum, timing.