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Repairing Glass Bowl Fuel Filters

Glass bowl fuel filter problems

James Berry Jan 3, 2019
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Question:

I love your magazine, and all of the how-to articles I find fascinating. Well, here is my question. I am finding a rust-colored powder in my fuel filter bowl and in the bottom of the carburetor. It looks like rust but I can’t understand where the rust is coming from. How could the rust or any sediment get past the fuel filter? I hope you have some ideas.

I noticed a loss of power on acceleration that led me to this problem, and there are air bubbles in the glass fuel bowl when the engine is running, but no fuel leaks. Is this normal or part of an underlying problem? Thanks for your help,

Jacob

Answer: Jacob, there are several problems that can be caused by a restricted fuel filter. The glass bowl fuel filters have a few additional problems the inline fuel filters don’t have. In a glass bowl fuel filter, the fuel enters the bowl through the center hole in the top of the filter housing and exits through a different opening on the top of the housing. The fuel filter element must seal tightly against the top of the fuel filter housing for all of the fuel to pass through the filter correctly. If the filter is not seated correctly the fuel could possibly bypass the filter, and small bits of sediment could also go out through any small gap.

There are several different fuel filter configurations so be sure and get the correct filter for your application. The filters come in different sizes and some filters have a large upper paper housing with small holes around the outside. Certain original filters used a stone-like element with an integral sealing gasket at the top.

When changing the fuel filter, install the fuel filter first and then the rubber gasket. Place the rubber gasket on the rim of the bowl and push it up into the housing and tighten the bowl screw. Be sure to check for any fuel leaks.

Getting air bubbles in the fuel bowl while the engine is running is usually caused from the gas boiling. A small amount of air bubbles are nothing to be concerned about, but if you have large bubbles or a large quantity of bubbles, the most common causes are listed below.


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On the top of the fuel housing there is an “IN” and “OUT” marked on the top. Make sure you do not have this mounted backward.


A low fuel vapor point. Check for a fuel line being too close to a heat source as this can cause the fuel to boil. Inspect to see if the fuel line is too close to the exhaust pipe or if the fuel line coming out of the fuel pump to the fuel filter is pressed against the exhaust manifold.

Check for air being introduced into the fuel. Inspect for a leak such as a cracked rubber fuel line or a loose fuel clamp.

The rust in the bottom of your fuel bowl is most likely caused from a rusty fuel tank. Today’s fuels containing ethanol blends can cause corrosion inside of your fuel tank, fuel lines, your carburetor or fuel-injection system.

The key problem is that ethanol absorbs water from the atmosphere. Fuel with 10 percent ethanol can absorbs up to 50 times more water than standard gasoline. Older gas tanks that are found in many classic cars vent to the atmosphere, this increases the probability that moisture will be absorbed into the gas tank at a rapid pace.


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Check for sediment in the bottom of your fuel bowl.


The end result of water in the fuel is phase separation, this means that the fuel separates into two layers: a layer of gasoline mixed with a little ethanol on top and a thinner layer on the bottom consisting of water mixed with most of the ethanol.

Water in the bottom of the fuel tank and inside the fuel lines will cause corrosion and rust, and the solvent properties of the ethanol will loosen and the resulting debris will end up in your fuel bowl or worse in your carburetor or fuel-injection system.

Well, Jacob, I hope this helps. And remember, buying non-ethanol fuel will assist with not having this problem in the future. Also, the complete glass bowl assembly with filter is available from several Corvette restoration parts houses if you find yours will not seal or has become corroded. Vette

Photography by James berry

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