GM454 Loosing power at higher RPM under load only

[jdejongh]

Have 1990 Commodore Regal w/ 454 and Volvo Penta IO. Idles fine, runs fine at Low RPM and runs fine at high RPM with no load (in Nuetral). When under load though once i get up to about 3000 RPM engine rapidly looses power (rpm). Almost like its starving for fuel??? Check ignition dist cap and rotor and replaced as it was a bit worn, retry and same symptoms. It has a holley 4 barrel carb and not sure if an adjustment might be in order?

other symptoms include: at higher RPM only (3000) (under load) get quit a bit of white smoke from exhaust.
Thanks in advance for any feedback

 

[Don S]

Re: GM454 Loosing power at higher RPM under load only

Revving the engine in neutral is a non test. You could pull all the spark plug wires off of one side and you could still get over 10,000 rpm.

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.

 

[jdejongh]

Re: GM454 Loosing power at higher RPM under load only

thank you for the suggestions. Would the billowing from exhaust under WOT narrow down the causes or is this unrelated?

Jeff

 

[Don S]

Re: GM454 Loosing power at higher RPM under load only

Probably unrelated. That very hot exhaust coming out of the exhaust getting hit by water as it exits the riser has got to create a little bit of steam, and it has to go somewhere.