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454XL Fuel System

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Cestlavie

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I have a 1993 Silverton 34X with a pair of 454XL engines with Holley 4011 carburetors, now I have been experiencing over the last couple of years, my plugs are very black, and the engines run rich, to the point that you can really smell the unburnt fuel. I pulled my carbs off and noticed a pool of fuel in the manifold; I sent my carbs in for a rebuild, and now they are done, the guy said there was nothing really wrong with the carbs other than a little bit of dirt in the bowls, the power valves and floats were good. Now he seems to think that I may have excess fuel pressure problem. The XL series only have electric fuel pumps and the manual says nothing about checking for exessive fuel pressure with these electric pumps it only goes into detail in non electric fuel pump engines (manual fuel pumps). Has anyone out there experienced or heard of this happening. The boat will be sitting until April so I wanted to do a check before launch, but if this is not a problem I will not attempt it
 
Yes... do the pressure test...But somehow you are going to have to find out what the correct pressure should be, you're probably going to need to get the OEM manual for your engines.I think you should be somewhere between 3 and 6 lbs. with the carbs. Fuel injection is a totally different story and runs upward of 25 lbs.....Good Luck....Lee
 
may also wanna check that a 4011 is ok for marine use. If ok, then check the calibration it delivers...may be too rich.

If the pressure is too high, adding a pressure regulator is straight forward.
 
The Holley 4011 is the factory carb that came with these engines. I do have the OEM manual, it says that "electric fuel pumps deliver 4 to 6 psi of fuel pressure" Then is tells you how to check to see if the pump works or not, nowhere does it state how to check the fuel pressure, the only description is deals with is the mechanical pumps. So what I get from the book is either the electric pumps work or they don't, there is not real pressure differential
 
electric pumps are subject to many of the issues of mechanical pumps...you need a fuel pressure gauge to check the pressure.
 
You'll have to make a "T" at the carb inlet, you'll need some tubing, a 3/8 tee to plug into your meter and a male and female inverted flare to tubing fittings.
Put the fuel pump feed into one side , attach the other side to the carb and the Tee to the meter. Then you can run your engine and read off the pressure.
It's better to be sure than running around in circles. Good luck....Lee
 
If you see reasonable fuel pressure (4 to 7 psi) then the float valve (needle and seat) is leaking by. That means a rebuild.

A trick you can try is this: With the motor in question fully warmed up and idling in neutral, slowly turn the idle mixture screws IN (CW) and observe the results. If the motor slows down and stalls, the carb is NOT flooding. But if it keeps running--and speeds up a bit, perhaps--then the carb is flooding.

Jeff
 
A good visual check usually helps too.

Also, several aftermarket suppliers to the "hot rod" community make adapter fittings that provide a clean solution to monitoring fuel inlet pressure on a Holley carb - a www search will give you pretty good insight as to what is available.
 
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