1997 Mercruiser 5.7 Bogs at WOT but runs great at 7/8 throttle

I have a 1997 Bayliner Capri 2050 with a 5.7 Mercruiser 260 hp. On wednesday evening we did a long run to restaurant and back, included an hour of no wake and 40 minutes of WOT or high speed cruise each direction. Boat ran fine. 4300 rpm, 52 mph 5 people on board. On Thursday morning, boat started normally, idled out of annchorage normally and accelerated normally to 3600 rpms on to plane perfectly. When I pushed the throttle the last 1/8 to WOT the engine bogged losing power and dropping to 3000 rpms. It felt like a choke had closed. When I pulled back 1/8 it jumped back to 3600 rpms and ran fine with no problems at all. Starts fine and runs fine except for WOT. When the engine bogs it is not gradual, it feels like a switch is being thrown and the same when I pull back from WOT it frees up and runs great, right where it would normally run with normal power etc.

Re: 1997 Mercruiser 5.7 Bogs at WOT but runs great at 7/8 throttle

Mines an 87 225 cc with a 5.7 260 mercruiser, was doing the same exact thing, I cleaned alll the filters and replaced the water fuel separator and rebuilt my carb and it ended up being the fuel pump was going bad...put a new one on and it runs great now.

Re: 1997 Mercruiser 5.7 Bogs at WOT but runs great at 7/8 throttle

Well could be lots of things. Look in the adults only FAQ and there is a thread in there called reasons for low WOT or something like that.

Go through those steps.

You really rag your engine out running it at WOT a lot. Especially for 40 mins straight.

Re: 1997 Mercruiser 5.7 Bogs at WOT but runs great at 7/8 throttle

LAC_STS said:

Well could be lots of things. Look in the adults only FAQ and there is a thread in there called reasons for low WOT or something like that.

Go through those steps.

You really rag your engine out running it at WOT a lot. Especially for 40 mins straight.

Click to expand...

Ayuh,.... I'll say,....

Check the Contents of the fuel filters....

Re: 1997 Mercruiser 5.7 Bogs at WOT but runs great at 7/8 throttle

Thank you for input.

To clarify, I didn't run at WOT throttle for 40 mins. straight. But a combo of high cruise and WOT. I am heading down to the boat tonight to try and start going through the process of checking issues, the one thing that stands out in my mind is how the boat runs perfectly at 3/4-7/8 throttle, easy power and acceleration but when pushed to the stops it bogs like a switch being thrown to 3000 rpms. Almost like the choke is being engaged when the throttle is pushed all the way but opens back up and accelerates to 3600 when pulled back just a bit.

Is there something in the choke that engages it like that for cold starts but would normally keep it from engaging once the boat is warmed up? a solenoid that uses some sort of temp input? I should also say that my oil pressure sensor is not functioning properly and wondered if there is some electrical input that would affect choke adjustment that is tied to that?

Forgive the stupid sounding questions. I"m a first time powerboat owner, just bought it a month ago and am working through a variety of items on the to do list, but until Thursday the boat has been running like a champ.