When it comes to efficiently mixing air and fuel, dollar for dollar, no fancy gizmo concocted in the last century can match the carburetor. Sure, the OEs ditched carbs for EFI nearly 15 years ago, but the carb remains the top choice of weekend warriors and hard-core hot rodders throughout the world. Although they haven't changed much in outward appearance since they were first invented, modern carburetors employ the latest in technological and manufacturing advances. That means fewer headaches and more power and reliability.
A prominent force in aftermarket fuel systems, Barry Grant has contributed to the evolution of carburetors since 1984. In addition to its line of Demon carbs, Barry Grant offers a full catalog of fuel-delivery components and carb accessories. After seeking their expert advice on how to plumb fuel systems, tune carburetors, and prevent common pitfalls, the collective minds of Barry Grant, Adam Campbell, and Victor Moore set us straight. Here's what they had to say.
Cooler weather calls for larger jets than warm summer weather, as do changes in altitude. As density altitude improves, an engine may need larger jets, and as density altitude deteriorates, smaller size jets may be required. "Generally, for every 1,250- to 1,500-foot increase in density altitude, jet size should be reduced by one number," says BG. However, some motors aren't as susceptible to density altitude changes as others. "A nitrous-powered car, for example, is far less likely to be affected by density altitude variations than a supercharged car. Furthermore, when using a density altitude gauge to determine jet changes, be sure to keep an accurate record of the changes. Since improvements can only be made through trial and error, it is imperative to keep detailed records of jet changes and how they affect e.t.'s."
Carburetor rebuilding intervals are usually determined by vehicle usage and application. A carburetor that sits unused over the winter and dries out may only require new gaskets. On the other hand, a carb that is run regularly with clean air filters and fuel filters may run for several years without any harmful effects. "The most common symptoms that indicate a rebuild is near are poor starting and driveability issues," explains BG. "Of course, these symptoms don't always indicate a rebuild is necessary, since they could just mean the carburetor is merely out of adjustment and needs retuning."
Putting a fuel system together the right way isn't cheap. Some hot rodders see a prefilter as a frivolous expense that can be avoided, but that's a good way to increase the probability of pump failure. "To protect a fuel system, whether electrical or mechanical, always mount a fuel filter before the pump," BG advises. "In high-powered, gear-style pumps, tolerances are so close that one grain of sand can seize them. Consequently, in a BG Mighty flow-through pump, the fuel filter is an integral part of the pump situated between the inlet port and the gearhousing."