won't go over 2krpms in gear - help

[fizzle15]

howdy,
i've got a 16.5 foot galaxy bowrider with a mercruiser 120 - and with just me in the boat - it won't go more than 2000 rpm's while in gear - so of course it won't plane out.
its got a 15pitch prop on it
and the engine is newly rebuilt - also have a rebuilt distributor - new cap and wires and plugs and condenser and what not.
the carb has never been cleaned or rebuilt.
but when in neutral the engine will rev up to for ever - i really never pushed it much further than 4500 but it seems like it could keep climbing.
but when in gear it will not go over 2000.
what am i missing - what would cause this?

thank you in advance

 

[bruceb58]

Re: won't go over 2krpms in gear - help

Has the boat ever reached proper RPM with that prop?

What is the compression of this rebuilt engine?

How old is the fuel? What are the condition of the fuel filters?

RPM without a load means absolutely nothing.

 

[Don S]

Re: won't go over 2krpms in gear - help

List of possible causes of low WOT (Wide Open Throttle) rpm.

In no particular order

Engine Won't Reach Operating RPM. Check

1. Fuel condition. Type and Octane possibly old fuel
2. Propeller pitch or diameter, damaged blades
3. Restricted fuel pickup tube or anti siphon valve Fuel System Test
4. Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
5. Marine growth on hull and outdrive
6. Wrong gear ratio in outdrive
7. Restricted carburetor air intake (clogged flame arrestor)
8. Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
9. Poor cylinder compression Compression Test
10. Carburetor defective, or wrong type.
11. Fuel pump pressure and vacuum
12. Boat overloaded, improperly loaded, or improperly trimmed.
13. Engine Overheating
14. Engine timing and ignition system operation
15. Remote control cables and linkage for proper travel to open throttle plates fully.