Along with its needle-seat...
Along with its needle-seat assembly, the float is a critical element to maintaining the fuel level in the carburetor float-bowl. The brown unit (top) is an original Pontiac float, while the black unit (center) is a modern replacement. Ruggles says the original is very susceptible to ethanol-related failure, while the replacement is not. The brass float at bottom is another modern alternative. However, Ruggles suggests that it be submerged in water and closely checked for minute air bubbles that could indicate an internal leak.
When preparing a typical Quadrajet for use in a high-performance application, as the Rochester engineers did, Ruggles specifically calibrates the entire fuel curve of each casting for its intended application. "We take into account engine displacement, compression ratio, camshaft specs, the intake manifold, and if tubular exhaust headers are being used. We also ask the owner what climate and altitude the vehicle will be operated in, and to a lesser extent, consider gear ratio, converter stall speed, or if a manual transmission is being used."
Replacing primary main jets on a Quadrajet alters the entire fuel curve, so metering rods are employed to precisely tune part-throttle calibration. "I don't recommend arbitrarily increasing jet size in any circumstance. In most cases, the primary jet is already adequate for performance use, even on emission-calibrated units," Ruggles says. "The factory was far more stringent with fuel metering at idle and light part-throttle, so this is where we focus our efforts. Arbitrarily increasing the existing jet size one or two numbers to accommodate for ethanol-blend fuel can lead to an over-rich condition."
An engine runs leanest at light part-throttle cruise and since ethanol is less-efficient than gasoline, the negative effects might likely appear as an overly lean condition. "Light-throttle surging, transition flat spots, or an overall lack of light-throttle response are symptoms to look for. It can oftentimes be remedied with a primary metering rod change or with a quarter to half turn of the Adjustable Part Throttle (APT) setscrew, if so equipped. "I strongly believe that when prepared correctly, there shouldn't be any issue running a Pontiac on E10 fuel."
We suggest that when using ethanol-blend fuel of any degree, you occasionally inspect your vehicle's entire fuel system, paying particular attention to its rubber fuel hoses and steel fuel lines, and replace any at the first sign of failure.
If using E10 in your vintage...
If using E10 in your vintage Pontiac is okay, E85 must be too, right? Wrong! E85 fuel is a high-level ethanol-blend of as much as 85 percent, depending upon the climate, and the fuel systems and engines that can operate on E85 are specifically designed and calibrated for it. One can certainly convert a vintage Pontiac to E85 operation, but that's an entirely different subject than what's presented here!
A point to keep in mind about our story is that it may not still apply if the EPA increases the ethanol-blend cap to 15 percent or even greater in future years. When that time comes, the hobby will once again have to endure a learning curve, since we'll be in uncharted territory.
Conclusion
After reviewing the facts about ethanol and hearing an expert opinion about its effects, it's apparent that though ethanol-blend fuel is here to stay, it doesn't signal the end of the hobby for all. We also found that it's quite possible most Pontiacs have already been exposed to low-level ethanol-blend fuel, and a vast majority of them haven't displayed any major negative effects. The best news is that when prepared correctly, any hobbyist can successfully run his or her Pontiac on a steady diet of E10 fuel without worry.