RPMs Reduced When Forward Gear Engaged

[mhinnc]

A4 in a 1972 C&C 30. In neutral motor runs as expected 3000+ RPM. Backed out of slip today okay, didn't notice a draw down of RPMs. Put trans in forward with throttle pushed up to gain headway, but the RPMs remained near idle RPMs, enough to move boat forward at a slow speed. From cockpit motor sounded/felt normal, just at a low RPM. Pushed throttle max and there was no change to the RPMs. Regardless of where I put the throttle, it remained near idle RPMs. I put the trans in neutral and pushed throttle up and got the expected 3000+ RPMs. Pulled throttle back and engaged forward, then pushed throttle up and again, just idle RPMs.

Any ideas where I should begin looking?

Any/all help is much appreciated.

[joe_db]

Step 1: check the prop for barnacles, lines, seaweed, etc.

[zellerj]

A collapsed exhaust hose may be the culprit. Without a load a collapsed exhaust hose will be adequate, but with a load it can restrict horsepower - and not allow full rpms to occur.

[Dave Neptune]

How many RPM's are you talking about? If the prop is fouled and the engine is at idle speed it would die once the throttle was advanced as there would be little flow to carry fuel to the cylinders unless the choke was engaged.
Do check the prop and take a good look at the throttle and choke linkage.

Also take a look at the plugs as to there color and dryness.

Did you check anything? Has there been any work on the engine recently? Did this problem happen all at once or did it creep up over a few outings?

What is the engine equipped with? Tach, gages, ignition, filters and fuel pump etc.

Dave Neptune