3.0L Mercruiser Losing Power

[fitzy]

I have a 1989, 17 foot Stingray with 3.0L 4 cylinder GM engine and Alpha 1 outdrive. It runs OK with a relatively light load (say less than 400 pounds), but struggles when I have more passengers (say in the range of 800 to 1000 pounds total or 5 to 6 adults). With lighter loads, I do 3500 RPMs and 28 MPH. At heavier loads, both RPMs and speed drop off considerably. Seems to have only become a problem this season. Any insights into the possible cause(s) of this condition and/or suggested diagnostic or corrective measures would be appreciated.

 

[guyjg]

Look at the weight limit on the Coast Guard placard...I bet it has a 650-750 lb. limit. You might install a 4 blade prop to improve planing. A complete tuneup can only help it.

 

[floatin radio]

WOT should be 4300 to 4800

 

[zootschief]

Sounds like maybe you have some growth on the bottom,or engine needs tune up.Take compression test to be sure engine is not sick.