We covered quite a bit of ground in Part One of our Rochester fuel injection re-do (April 2003). After briefly discussing the history of fuel injection systems in general, and Rochester's mechanical version in specific, we described the Rochester F.I. unit's fuel meter. We then followed along as our Fuelie expert, Chuck Smith of Chuck Smith Performance Services, reassembled said fuel meter on our subject '60-vintage system. In this installment, the second of three, we'll cover the air meter re-assembly process, as well as the installation of the injectors, the fuel lines, the vacuum lines, and the throttle linkage.
Is It Really That Simple?
In Rochester Rx, Part One, we stated that "Overhauling A '60 Rochester Fuel Injection Unit Is Simpler Than You Think." Now, we're not backing off of that statement, but we do want to clarify it a bit. Dave McLellan calls the Rochester mechanism "a complex jewel of a system" in his book, Corvette From the Inside. And it is, especially when it comes to the fuel meter. The unique lever and pivot assembly, along with the spill plunger, which we described last time, are complex. In other words, there's a lot of parts to keep in proper working order! On the other hand, that complexity is in the details. Once broken down into its various subsystems, the Rochester mechanical fuel injection system reveals its mysteries in an understandable way.
A Rochester unit has three basic systems: The fuel meter, the air meter, and the intake manifold. We've covered the fuel meter; as for the manifold, we'll just note that Zora Arkus-Duntov (along with Joe Dolza) was instrumental in its development, which led to "ram pipes" to each cylinder, as well as the two-piece design that helps keep the injection nozzles cooler. (Jerry Burton discusses Zora's role in the Rochester project in his book Zora Arkus-Duntov: The Legend Behind Corvette.) That leaves us with the air system. As we said before, the fuel meter lever and pivot, and therefore the spill plunger, are controlled by three diaphragms. These diaphragms are activated as necessary by vacuum. These vacuum signals are fed to the fuel meter from the air meter via various vacuum lines.
Air, Fuel, And Mathematics
The appropriate vacuum signals are created in the throttle body by running the air through a venturi. This venturi is created by placing a diffuser cone in the intake opening. As air rushes around the cone and past the throttle valve, pressure drops or increases, depending on the circumstances. The vacuum signal corresponds mathematically to the flow of air entering the engine. This carefully calculated vacuum signal then activates the diaphragms in the fuel meter, which in turn activates the moveable pivot and lever assembly, which moves the spill plunger, which allows the proper amount of fuel (mathematically calculated, of course) to reach the injector nozzles. This creates a air/fuel ratio ranging from 12.5:1 (performance) to 15.5:1 (economy). Here it is in slightly more practical terms:
* A high airflow/high vacuum signal raises the linkage, but lowers the spill plunger. This shuts off the spill port, raising injection pressure and richening the mixture.
* A low airflow/low vacuum signal lowers the linkage but raises the spill plunger. This opens the spill port, bleeding off injector pressure and leaning the mixture.
* At idle, the air meter vacuum signal is very weak. This allows the control diaphragm to drop, which opens the spill port all the way, sending most of the fuel back into the float bowl.
There is also an electric choke system, which we've explained below, and a fuel cut-off diaphragm (for coasting and deceleration) that is vacuum activated. As with all our vacuum lines, we'll make sure this one is hooked up and getting the proper signals.
LET'S GET TO IT, ALREADY!
We asked our expert, Mr. Smith, if he had any advice concerning the Rochester F.I. air meter, and it turned out to be the same as for the fuel meter: Everything needs to be clean, and it needs to be properly assembled and adjusted. With these tasks accomplished, Chuck says, "It should work just fine." All the Rochester's parts--hard lines included--were sent out to be sonically cleaned before re-assembly. Chuck also uses new hoses and gaskets throughout. As for proper assembly and adjustment, we'll jump back in and show you how it's done. Next time, we'll deal with a pair of Rochester bugaboos that are often mistaken for more serious problems: The fuel pump and the distributor.
YOU MUST READ THIS BOOK!
In Part One, we extolled the virtues The Chevrolet Ramjet Fuel Injection System, which is being reproduced by Corvette America. (Route 322, Box 427, Dept. VM, Boalsburg, PA 16827; 800/458-3475, www.corvetteamerica.com). In preparing to write Part Two of "Rochester Rx" I referred to this pamphlet again and again to make sure I understood how the unique system works. Each subsystem is explained in detail, and the line drawings are top-notch; several have been used in this story. It's fascinating and useful reading, for the do-it-yourselfer the merely curious, and for those seeking to know everything about vintage Corvettes. Like we said before, when it comes to taking care of a Rochester F.I. system, you can't have too much information.