Engine won't rev past 2000rpm under load

[theobot]

I have 1985 Wellcraft Gran Sport with twin 454 MARINE POWER motors(1996).
In October of last year I blew the V-drive on my starboard motor. I hauled engine out and installed a used V-drive. While the engine was out and at my shop the only thing I did is replace spark plugs, wires, cap and rotor. Dropped the engine back in and now for some reason it won't rev up past 2000rpm under load, it bogs down and backfires. At neutral works perfect, idles fine and revs up. Since that has been happening, I have rebuild the carburator twice, replace cap and rotor again, checked all wires, had the timing checked three different times by three different people and changed coil. It is still doing it. For the life of me I can't figure it out. It was working perfectly before the V-drive blow up. All it did was sit in my shop on an engine stand for six weeks until I found the V-drive. Any ideas?

 

[Lyle29464]

Re: Engine won't rev past 2000rpm under load

2 plug wires crossed on a 454 will do this. 18436572 S 12756348 R

Then I would head for bad gas or a vacuum leak, power valve

 

[Bondo]

Re: Engine won't rev past 2000rpm under load

Since that has been happening, I have rebuild the carburator twice,

Ayuh,... Welcome Aboard,.... How much Crud was in the carb,..?? How 'bout in the fuel Filters,..??

Is the gas tank givin' up it's fuel alright,..??

 

[theobot]

Re: Engine won't rev past 2000rpm under load

2 plug wires crossed on a 454 will do this. 18436572 S 12756348 R

Then I would head for bad gas or a vacuum leak, power valve

Already checked the wires many times. I will be checking for a vacuum leak today. As far as bad gas is concerned, I tried running both motors with the other side tank and it still happens while the port motor runs fine. What about the power valve?
Thanks

 

[Don S]

Re: Engine won't rev past 2000rpm under load

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.

 

[theobot]

Re: Engine won't rev past 2000rpm under load

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.

Already checked most of them, I will definately go down the list, thanks.