Fuelie Facts And Fiction: Mechanical Fuel-Injection Systems

Steve Temple Mar 14, 2013 0 Comment(s)
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In addition, as doctors recommend to anyone whos middle-aged, exercising a fuelie on a regular basis is probably the best thing you can do for it. Since its a vented system, sitting still for extended periods of time can allow the fuel inside the fuel meter to evaporate and deposit a film of varnish. This buildup will eventually gum up the works. Also, it goes without saying that proper assembly and adjustment are essential. (The accompanying photos and captions illustrate what happens when these principles arent followed assiduously.)

At this point, things can get complicated, as there were several variations on the FI theme, which well also highlight in the captions. As Rochester Products gained familiarity with the FI system, manufacturing methods were simplified (sand castings became die castings, for example).

Vemp 1303 10 Z Michanical Fuel Injection Systems Internal Check 2/21

Also, the subsystem that provides for cold-weather enrichment was improved, and the one that initiates fuel flow for engine starting was refined as well. Eventually attempts were made to increase the FI systems tolerance for hot weather. Even with all these changes, the fundamental operating principles remained unchanged for as long as mechanical fuel injection was in production.

In view of these changes, Lockwood points to the preferred original parts to use, along with some modern ones that can be integrated into the system to improve both its function and reliability, all without hurting the cars collectibility.

Based on his years of experience, he notes out that there are two types of fuel-injection systems: those that have failed, and those that are going to fail. He attributes this eventuality to three aspects: wear, engineering flaws, and Bubbas (his term for general-purpose mechanics who arent familiar with the specifics of a Ramjet). Lockwoods basic advice: Look for damageand dont assume it doesnt matter.

Even when new, the Ramjet system was difficult to service, and few mechanics had the experience or tools to properly adjust it. (As a result, one unusual source for FI parts is from mechanics who replaced the system with a more familiar carb setup, and simply left the stock hardware on the shelf!) Despite this initial disdain by the uninitiated, the Rochester FI is now recognized as a classic design, seriously sought after by collectors of C1 Corvettes.

Thats in part because the Ramjet was a major improvement over the carburetors of the day. Unlike a carb, in which the venturi signal directly pulls fuel into the air stream, the venturi signal of the fuel injection tells the fuel meter how much fuel to pushor, more accurately, injectinto the air stream. Because this fuel-metering scheme was so much better than that of conventional carburetors, the problem of erratic mixture changes due to fuel slosh during hard cornering was completely eliminated.

Carburetors also suffered from a limited manifold size, due to the requirements of the operating range and the need for a hot spot during engine warm-up. The front cowl, carburetor, and air cleaner had to be low for clearance, and that height restriction interfered with achieving the ideal combination of driveability and high performance.

The Ramjet FI had none of these problems, but it had other issues. Being mechanical, it lacks the sensors that allow modern EFI systems to compensate for a wide range of operating conditions, such as changes in temperature and altitude. In spite of this drawback, it does a remarkably good job of adjusting fuel flow in response to changes in air density. Vintage racers looking for every advantage might find a reason to make minor adjustments on race day, but for normal street driving, the FI system can be calibrated once and then just left alone.

And when that Ramjet is working properly, the throttle response can make for a thrilling ride down memory lane.

Fuel Injection Repair and Calibration Jim Lockwood (530) 644-2517
Bob Webster (530) 644-1163
John DeGregory (724) 832-3786
Frank Antonicelli (717) 566-5039




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