1998 regal commodore

[arise]

Volvo penta 5.0 dual prop just won't go over 4000 rpm Compression check ok New fuel pumps and filter New check valve at tank New plugs, cap and rotor Fresh oil New manifolds( not that that's relevent) Why? Could props need balancing? How do you know When props need to be balanced. I like this boat, so I'm not trying to get a new one. 500 hrs

 

[Howard Sterndrive]

Did it get gradually worse, happen suddenly, or has it ever gone over 4000?

Don S.'s master list:
Here is a 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.

 

[dypcdiver]

What props have you got? It is quite a heavy boat.