Idleness Is A Fuel's Desire

Broken down into its component parts, a fuel system comprises the tank, fuel lines and fittings, either a mechanical or electric pump, filters, and a regulator. If you haven't plumbed a fuel system since the days of running a hardline from the tank to a mechanical pump at the engine, with a filter between that and the carburetor, you'll be surprised how complicated things got. But then, one look at the fuel system on your daily driver will confirm that! Fuel injection has been around since the Fifties on production cars, and has been used exclusively on cars sold in the United States since 1990. While many hot rodders still prefer to run a carburetor, an increasing number are embracing fuel injection technology. While we won't discuss the ins and outs of fuel injection here, its basic requirement is that it be fed gasoline under pressure in order to operate, at much higher pressures than a carbureted fuel system requires, and indeed at much higher pressures than a mechanical pump can generate, which is why you'll find electric fuel pumps on fuel injection systems. Edelbrock recommends a pressure of 5.5 psi for its Performer carburetors, compared to 14 psi for a stock '89 GM 305ci throttle body unit and around 45 psi for tuned port injection systems. Quite a difference!

Of course you can run an electric pump on a carbureted engine. Holley's Red pump pushes 7 psi, and a Carter even less; coupled with an in-line regulator it's possible to control the pressure at the carburetor. But why would you want to replace a perfectly good mechanical pump anyway? Sure they're low tech, quiet and reliable and don't require any wiring, plus they shut off when the engine dies, but they're also located in an area of extreme heat, which can cause vapor lock, and require the engine to be cranked over excessively if it hasn't been fired for a while, in order to pump gas to the carb, as they first have to create a vacuum in order to pull the gas all the way from the tank. This period of cranking the engine over before firing can promote excessive bearing wear. If you pump the gas pedal, especially on a hot engine that may be having trouble starting, depending on the carburetor it may set the choke mechanism, which can lead to bore wash, where fuel will wash the cylinder walls, again promoting undue wear. On the plus side, they're easy to plumb, and simple to find a replacement should you have to do so while on the road. No small consideration with the mileage we're putting on our hot rods these days, and one of the reasons SO-CAL Speed Shop likes to use factory style mechanical pumps on their own and customer cars. Indeed, you may not even be aware that Holley sells mechanical pumps alongside its range of electric versions.

A problem that we're hearing more and more these days with new fuel compositions, and fuels such as E85, is issues with pumps and even flexible lines. The diaphragm in some pumps, especially older ones, may break down, owing to their intolerance of these new fuels. I have had firsthand experience of this, with the diaphragm in a cheap electric pump turning to a sticky gloop after sitting for a few months with fuel in it. This is one reason why the OEMs have switched to plastic fuel lines rather than rubber.

If you've been messing with old cars for a while, your experience of electric pumps may be limited to something like the Holley Red or Blue pumps, but the aftermarket has moved along with the OEM fuel systems, and in-line and even in-tank pumps are now commonplace. There are several advantages to in-tank pumps; the fuel helps keep the submersed pump cool and the risk of fire is reduced, as liquid fuel won't explode. Any pump will work better the closer it is to the fuel tank, and in-tank pumps totally eliminate the need to create a vacuum and "pull" fuel up to the pump, ensuring a steady supply. This is especially important with an injected engine, which will stutter or die at even the briefest of lapses in fuel supply.

Of course to maintain that steady supply, the pump pickup has to be constantly immersed in fuel. According to John Pazik at Tanks, Inc., "If the tank is not equipped with a reservoir tray to keep the pump inlet immersed in fuel, the pump will suck air when turning corners or accelerating and the engine will stumble." Many of the company's die-stamped tanks are manufactured with an internal reservoir tray, but they also offer a pump kit which has the tray, and can be installed in your existing tank simply by cutting a 41/2-inch hole and a series of mounting holes, with no welding required. Rock Valley also manufactures tanks with an internal pump, though theirs is mounted in a canister type reservoir rather than a tray, both doing the same job. The company makes a number of stainless steel tanks for early cars, as well as dedicated in-tank pump and sender kits for specific fuel tanks, though welding is required to fit these, either by the customer, or by shipping the tank to Rock Valley to be modified.

An advantage to using a new fuel tank like those above is that it'll be free of debris and will already be equipped with an outlet of sufficient diameter to deliver the quantity of fuel required. This is something to think about if you plan to replace your entire fuel system but retain the stock tank. While the OEM-style in-tank pump has advantages, in-line pumps are also available, whether you plan on running EFI or carbs, or just don't want to modify your tank. If this is the route you take, according to Jesse Powell of Aeromotive, "An external fuel pump, either electric or mechanical, would ideally be placed as low and as close to the tank as is possible. You want to minimize the vacuum the pump has to make to get fuel from the tank. This avoids premature fuel vaporization and extends the fuel pump's duty cycle and ability to supply liquid fuel as fuel temperature elevates on hot days. Keep in mind that any liquid's boiling temperature drops as you pull a vacuum on it."

We mentioned constant fuel supply is important to an injected engine, and this is because, unlike a carburetor, there's no "reserve" fuel, such as a carb has, in the float bowl or bowls. Injection systems have a return line that sends unused fuel back to the tank, and this should be at least 5/16-inch in diameter if the supply line is 3/8-inch. The return line should also feed back to the bottom of the fuel tank. The use of a return line reduces the chances of fuel boiling and causing vapor lock problems, because the fuel is never kept close to a hot engine for very long.