454 inboard losing power

H

hgm444

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Jul 29, 2012
Messages
3
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

picklenjim

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Mar 11, 2009
Messages
528
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.
 
H

hgm444

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Jul 29, 2012
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Re: 454 inboard losing power

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

hgm444

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Re: 454 inboard losing power

Also the engine has just under 500 hours on it.
 
J

joewithaboat

Lieutenant Junior Grade
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Jul 3, 2011
Messages
1,172
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.
 
D

dollarten

Petty Officer 2nd Class
Joined
Jul 28, 2011
Messages
136
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
 
9

92rslt1

Petty Officer 2nd Class
Joined
Jun 26, 2010
Messages
102
Re: 454 inboard losing power

hgm444 said:
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.
Click to expand...

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.
 
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