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Fuel System Service
This month we will cover the fuel system of your vintage Pontiac, in keeping with the theme of past articles, we begin with the assumption that your car is in generally good condition and requires merely a thorough check-up before you begin driving it again.
The number one item of fuel system service is to thoroughly inspect the entire system for any possible leaks, and carefully check all rubber hoses for deterioration. Proper inspection of rubber hoses includes visual inspection for cracking of the outer surface, apparent leakage at connections and along the entire length of hoses, plus squeezing the hose to determine if it is either too soft or too firm. In some cases the hose will swell up and become very soft due to modern gasoline, or other chemical additives that may have been used such as dry gas or a fuel system cleaner. The other extreme is the nearly rigid stiffness of hose as affected by heat and age. In either case, this affected hose must be replaced with new; and you want to buy your hose from a reputable auto parts supplier and make sure they know you are using it as part of the fuel system. Good quality hose will usually be printed with the wording “fuel and emission hose” to be sure there is no mistaking its intended use.
We are fortunate that our vintage Pontiacs used very little rubber hose as the cars came from the factory. Typically there is a section between the fuel tank and the steel line on the frame, and another section from the frame line to the fuel pump. This second rubber line is actually a composite assembly of rubber and brass fittings as originally installed. Regardless of what combination of hoses and lines are used on your car, it is essential that you inspect them at least once a year, and preferably twice; spring and fall. A realistic life expectancy for synthetic rubber hose under the conditions that the majority of us use our cars is probably 4 to 5 years. Beyond this age, a failure could result in a relatively short time, so pay attention to any fuel odor or spots on the pavement under your parked car.
NOTE: If you find any fuel hose on your car that has swollen and become very soft, it is very likely that chemical action has caused this and the diaphragm(s) in your fuel pump are also highly suspect for the same kind of damage. The vacuum advance unit of your distributor could also be affected as fuel fumes do come in contact with it.
Once you have inspected the fuel lines, examine the fuel pump, sediment bowl and the carburetor for any signs of excessive leakage. It is nearly impossible to prevent fuel from weeping at the edges of the fuel pump and sections of the carburetor where the gaskets protrude. The difference between slight weeping and a fuel leak is the presence of dirt. Any connections or seams between fuel pump or carburetor components will attract an accumulation of dirt due to trace wetness. An actual leak will have sufficient flow of fuel to wash away the dirt, so any areas that are leaking are usually conspicuously clean. Bear in mind that the fuel line from the tank is subject to slight vacuum when the engine is running, so it is more likely to leak as soon as the engine is stopped, this also applies for the sediment bowl section of the fuel pump. The pressure side of the fuel system includes the pump diaphragm and the line connected to the carburetor, also an accessory sediment bowl, if installed. This section of the fuel system is more likely to leak with the engine running.
The sediment bowl in the pump functions to capture foreign material or water before it gets to the carburetor. There is also a screen installed in the fuel inlet of the carburetor that should contain any particles big enough to cause the needle valve to stick open. If you want to install a pleated paper fuel filter, it should be placed in the line between the pump and carburetor, fuel filters are designed to be in the pressure side of the system and not on the suction side. You could cause vapor lock problems by trying to draw fuel through the filter.
The stipulations regarding synthetic rubber fuel hose also apply to the diaphragm in your fuel pump. If it has been more then 10 years since your pump was rebuilt, I would highly recommend that you buy a rebuild kit and replace the diaphragm(s). Be sure to buy a new kit; do not use N.O.S. rubber parts in the fuel pump! If you carry a rebuilt or N.O.S. fuel pump in your trunk for roadside emergencies, it also needs to have a new diaphragm installed. The synthetic rubber in recent years is designed to be compatible with today’s gasoline; any rubber older then about 10 years is suspect. From what I have read, fuel formulations seem to have stabilized in the past few years and the synthetic rubber compounds now available should perform well years into the future.
I personally do not change the valves in a fuel pump I know to be working, only the diaphragm. I treat the vacuum section of a compound pump the same way; if it works I only service the diaphragm. If you don’t seal the new valves absolutely air tight in the housing, the fuel pump will not work at cranking speed. The fiber disc valves of factory fuel pumps seem to be unaffected by gasoline formulations and I’ve not had any problem leaving them in place.
Most eight cylinder cars have the compound fuel pump installed, while you are inspecting fuel lines, be sure to look at the vacuum lines as well. A vacuum leak will result in poor windshield wiper operation and could also cause rough idle or stalling. Since the vacuum connection to the wiper motor came from either end of the intake manifold, a leak could cause a burned valve at that end of the engine if not corrected. Beginning in late 1951, the compound pump used a glass sediment bowl held in place with a heavy wire bail and thumb wheel screw. The cork gasket for the bowl is quite thick to cushion the glass, but this thick gasket compresses with age and the bowl becomes loose, so be sure to check the thumb screw regularly. I had an intermittent leak on my ’53 due to this, now I check the screw several times each season!
Pontiac was careful to design their fuel system to work in hot weather without undue concern for vapor lock. The fuel line is routed along the frame opposite the exhaust system and the carburetor has a shield to deflect radiant heat. The most likely cause for vapor lock on an ETC-era Pontiac is a stuck heat riser valve, so you want to be sure that yours is in good working condition. Modern gasoline is more aromatic then it was 50 years ago, especially the higher octane, this can cause problems in hot weather. I personally try to park my car facing into the wind when ever possible; I also raise the hood during short rest stops of 10-15 minutes to allow engine heat to readily escape.
Despite snide comments from the fuel injection people that a carburetor is nothing but a calibrated leak; it is in fact a delicate, precision instrument and if handled by an expert, will perform quite well. My own experience with the Carter WA-1 and WCD carburetors has been very good. Fortunately none of the Carter carburetors from the ETC-era has a synthetic rubber accelerator pump plunger, they are leather and very durable. Repair kits are readily available and once the carburetor is properly adjusted, it will perform reliably without further attention for thousands of miles. Unfortunately special tools are required for the critical adjustments of Carter carburetors being rebuilt, if you determine that your carburetor is not working properly, I recommend that you send it to a reputable carburetor specialist for repair.
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