Mercruiser Not Accelerating after Rest

[NJlakeboater]

I have a 4.3L Mercruiser Alpha1, Gen2. Here's what's happening. A cold start and everything is fine. No problem accelerating. Cruise around for 10 to 15 minutes, find a nice place to anchor and hang out. An hour later, starts fine, cruise to a new spot, no hesitation, easily get up to max cruising speed (30-35 mph.) Hang out for an hour or two, start up and go, but when in gear, the engine won't get up past 1300 RPM and will not get on plane. If I put it in neutral and the engine will rev up just fine. I took it to my local marina and of course the mechanic can't replicate the symptom. Any ideas out there? Some have told me it sounds like bad fuel, but if that's the case, why does it rev up in neutral? Any ideas would be a great help.

 

[Scott Danforth]

welcome aboard

reving in neutral doesnt prove anything, as your motor would rev to destruction in neutral with only 2 cylinders running (it doesnt take much of any fuel at all to rev in neutral without load

it takes about 100X the amount of fuel to reach full RPM while under load

your running out of fuel or you have bad fuel

either your vent is plugged (pull the fuel cap next time you have an issue, if you hear a hissing noise, your vent is most likely plugged)

or your anti-siphon valve is plugged

what is your fuel pressure? is this the '03 in your signature? is this a carb or MPI motor?

 

[NJlakeboater]

Thank you for your quick response. The load on the engine didn't even occur to me. I don't know my fuel pressure, yes the Sea Ray in my signature, and yes, a Carb, Thunderbolt V Ignition. I have to update that signature.