Getting the fuel to the carburetor...
Getting the fuel to the carburetor is a simple task if done right. But there are things that can go wrong, and they will show up on the track in the car's performance.
Fuel lines, filters, pumps, and regulating devices exist for a specific task-to deliver gasoline or alcohol from the fuel cell to the carburetor, and, in a bypassing system, return it to the fuel cell. Pressures and volumes vary depending upon the kind of fuel used (gasoline or alcohol) and the type of fuel system employed. With routine maintenance, a good fuel system will pay dividends. However, many cars are fitted with systems that fall below the necessary standards.
BG Fuel Systems has encountered some common concerns when handling customers' tech questions. The company put together a list of the most common mistakes in competition fuel systems and a guide for correcting them:1 Incorrect fuel lines Do not use 11/44 to 31/48-inch outside diameter lines on a racing fuel system between the fuel cell and the pump. Racers often joke about their first race cars and how the fuel line was so small it functioned as the main jet. Make sure the fuel is supplied through lines that are the correct size for the application. Remember, the fuel line's size is determined by the system, not the vehicle. Push-Lok, stainless steel braided hoses, and aluminum tubing are the most common fuel lines used on race cars.
Use adequate lines when bringing...
Use adequate lines when bringing the fuel from the tank to the pump. If you starve the pump, you're going nowhere fast.
2 Right-angle hose-end fittings from the pump to carburetor Avoid forged 90-degree elbow fuel fittings as much as possible. Although they are inexpensive and readily available, they're restrictive and frequently cause fuel flow troubles. Hose ends with angles of 90 degrees and 45 degrees should also be avoided if possible. Should it become necessary to use one, use radiused hose ends (90-degree bends) which have much better rates of flow. They're manufactured from aluminum, equipped with swivel ends for a positive seal, and are easy to install.
3 Fuel pumps unsuitable for alcohol An alcohol fuel system differs from the gasoline system in several crucial ways. Fuel pressures in a gasoline system are typically maintained between 7 and 9 psi throughout the rev range. Alcohol carburetors require low pressures of around 4-6 psi at idle and 9-11 psi at fully open throttle. This is necessary to prevent the carburetor from flooding at idle and under light engine load, yet maintain the extra volume necessary for maximum acceleration. Engines producing around 500 hp can be fueled with a 15-psi mechanical pump in conjunction with a throttle bypass valve. However, for engines over 500 hp, a belt-driven system with a diaphragm valve or poppet bypass should be considered. For overall reliability and performance, a belt-driven system is usually the better choice. When using a diaphragm bypass, BG Fuel Systems recommends it be installed close to the carburetor for faster response.
One of the most effective...
One of the most effective ways of regulating the fuel pressure of a 15-psi mechanical pump is the throttle bypass system.
4 Incompatibility between bypass and pump Throttle bypasses were designed to operate with block-mounted pumps and, similarly, diaphragm bypasses with belt-driven pumps. Never use a throttle bypass with a belt-driven pump. They must function in pairs and are not to be mismatched.
5 Unsuitable fuel filter Fuel filters with conventional paper elements must not be used with alcohol. Alcohol absorbs water, so the paper and the bonding materials deteriorate quickly. As a consequence, particles can enter the float bowls or get stuck in the needles-and-seats and main jets. Furthermore, it's equally important on alcohol applications to avoid filters with inadequate flow rates and inlet and outlet sizes that are too restrictive.
6 Neglecting routine maintenance on an alcohol system Although alcohol fuel additives can help prevent corrosion and provide lubrication for pumps and other components, alcohol can severely corrode metal objects, especially aluminum, if allowed to remain in contact too long. There is no substitute for a strict maintenance program. It will prolong the life of the carburetor and fuel system and also keep it trouble-free.