454 inboard losing power

[hgm444]

I have twin 1991 454's. One engine lacks power and will not achieve RPM. Starboard engine idles fine but does not sound as crisp as the other. When accelerating with both controls the same port is at normal 3200 rpm starboard will only run at 2700 rpm. WOT will only run at 3300 RPM. What I have done: Installed new plugs, wires, cap and rotor. Changed cartridge fuel filter and bulk head filter. Rebuilt carburetor (Quadrajet). I have the ability to switch tanks so I ran both engines off of the port tank with no change. Engine starts fine and does not miss. Linkage does open up all the way and the choke is ok.It acts like it does not get enough fuel.

 

[picklenjim]

Re: 454 inboard losing power

You need to check if the upper throttle plates on the secondaries which are vacuum operated are opening. They open by vacuum and are not connected to the linkage. They also lift the metering rods as they open allowing more fuel. If possible run it with the flame arrestor off and rev the engine and watch if the big plates on top of the secondaries are opening. If you can check it running under load it would be a plus.

 

[hgm444]

Re: 454 inboard losing power

Thanks, I did check them (but not under load) and they are opening.

 

[hgm444]

Re: 454 inboard losing power

Also the engine has just under 500 hours on it.

 

[grewvin1]

Re: 454 inboard losing power

Timing has been checked?

 

[joewithaboat]

Re: 454 inboard losing power

You may want to run a compression test, pretty easy. Then based on what you find... a leak down test.

 

[dollarten]

Re: 454 inboard losing power

You will have to have someone back by the engines and see if they are opening completely. when the engine is under load There is a secondary lock out that works in conjunction with the upper air valve to prevent the secondary air valve from opening . If it ( the lockout mechanism ) is interfering ,the secondary air valve will not open . Just a thought

 

[92rslt1]

Re: 454 inboard losing power

I have twin 1991 454's. One engine lacks power and will not achieve RPM. Starboard engine idles fine but does not sound as crisp as the other. When accelerating with both controls the same port is at normal 3200 rpm starboard will only run at 2700 rpm. WOT will only run at 3300 RPM. What I have done: Installed new plugs, wires, cap and rotor. Changed cartridge fuel filter and bulk head filter. Rebuilt carburetor (Quadrajet). I have the ability to switch tanks so I ran both engines off of the port tank with no change. Engine starts fine and does not miss. Linkage does open up all the way and the choke is ok.It acts like it does not get enough fuel.

Does it make a moaning sound?
Does it pop through the intake?

IMO sounds like a fuel issue with the info you have gave. Sounds like its starving. Is it mechanical pump? It might not be getting the volume it needs to run properly at wot. try swapping pumps, if its mechanical check the pushrod and cam for wear while its off.