Not Getting Max RPM at WOT on 7.4Lt 380 Horizon MPI

[ebigelsen]

I have a '99 380 Dancer that's been amazing, however, I'm not getting maximum RPMs at WOT. I always check for WOT performance at the beginning of the season with a clean bottom to get a baseline, and to see if anything isn't working right.

I traditionally get to 4,500 RPM at WOT (should be 28kts according to SeaRay), but cruise at 3,400 RPM (approx 18kts) with 1/2 fuel, 1/2 water, supplies, and 4 people. This year I'm only getting about 4,200 - 4,300 RPMs at WOT (approx. 22-23kts). The engines seems to be performing well - FWC is cooling, new oil & filters, clean air filters, etc.

I suspect it might be my props since I didn't get them professionally cleaned or trued (I skip that once in a while when the wheels look good, and there's no visible sign of wear or damage), however, I cleaned them up reasonably well with a wire brush and emory cloth.

Before I begin to suspect a possible engine issue, and start compression testing, i want to see if anyone else has a similar issue, and confirm my suspicions that it's probably the wheels. Thanks!

 

[Southpaw II]

I would check spark plugs first. I have different engines, but lack of RPM is the first thing I see about every 3 years. Changing plugs fixes it. Good luck.

Don

 

[RollerCoastr]

One of the first things to lead me out of the engine room and focus my attention to stuff underwater is that both engines are performing well and similarly.

 

[CliffA]

One of the first things to lead me out of the engine room and focus my attention to stuff underwater is that both engines are performing well and similarly.

+1......chances of both engines having the exact same mechanical/electrical/fuel supply trouble at the same time are extremely slim.....a drop of just a few hundred rpm's at WOT can easily be caused by a fouled bottom or running gear....or extra weight in the boat or water conditions or wind etc....

cliff

 

[ebigelsen]

I would check spark plugs first. I have different engines, but lack of RPM is the first thing I see about every 3 years. Changing plugs fixes it. Good luck.

Don

Thanks for the recommendation to check plugs which happen to by 3 seasons old. It's usually a process of trial and error.

 

[ebigelsen]

I've had the boat for 10+ seasons, and know her pretty well. Aside from worn plugs which someone already suggested (that's a fairly easy and reasonable inexpensive thing to try), I suspect the props might be off. The bottom is clean with a second season of Pettit HydroCoat which I touched up earlier this Spring. The mystery will be solved.