FIAT 124 Maintenance Manual

Welcome to my guide on FIAT 124 Spider engine maintenance and modification. Spiders are great cars, born in the mid 1960's when sports cars were fun to drive, affordable, and easy to work on. They remain a hobbyists’ dream. In 2002 I started to compile the various pieces of knowledge I obtained over the years into guides, first on carburetion and intake/exhaust systems, then, in 2004, a guide (more like a pamphlet) on fuel injection. I revised both guides over the years and finally compiled everything into this single document. My goal is to help you enjoy your FIAT as much as I enjoy mine.

The Otto Cycle
The most common type of operation for automotive engines is the four-stroke cycle, also known as the Otto cycle. Conceptualized in the 1870's by Nicolaus Otto (and others), the cycle has four stages of operation, beginning with the engine at Top Dead Center (TDC), when the piston is furthest from the crankshaft:

• Intake: The intake valve opens and fuel and air are drawn into the engine as the piston is drawn down.
• Compression: The intake valve is closed and the piston rises, compressing the mixture.
• Power: The compressed mixture is ignited, the resulting explosion forces the piston down.
• Exhaust: The exhaust valve opens and the spent gases are forced out as the piston rises.

If you want to know more about the Otto Cycle theory and all of the mechanical
engineering concepts that are involved pick up a copy of “A Practical Treatise on the ‘Otto’ Cycle Gas Engine” by William Norris, Longman, Green, and Co., London, England, 1896. At the time of this writing it is available for download on books.google.com. It is a very old book but is wonderful at describing the basic concepts of an automobile engine. FIAT 124 Maintenance Manual,FIAT 124 Service Manual,FIAT 124 User Manual.

Lambda
Fuel Injection systems and Carburetors have a common goal to reach an air to fuel ratio of 14.7:1 and maintain that ratio through changing engine loads. The ratio is known as the stoichiometric air-fuel ratio for gasoline. It is commonly referred to as lambda. Any mixture less than 14.7:1 is considered rich; any mixture above is considered lean. The air fuel mixture is established on a carburetor by setting mechanical devices, such as air bleeders, fuel jets, and emulsion tubes. On a fuel injection system the mixture is constantly adjusted by a computer that varies the amount of fuel sprayed into the cylinder. Both systems rely on a stream of measured air, regulated by a throttle, to deliver atomized fuel into the engine.

Carburetor
A carburetor is a device that mixes fuel and air together for use in an internal combustion engine. A throttle regulates the amount of airflow into an engine and the subsequent increase in air speed and drop in pressure. A restriction in the carburetor barrel, known as a venturi, forces the air stream to increase in speed as it passes by a number of fuel delivering orifices. The orifices enrich the stream of air with fuel. The resulting mixture is a near lambda combination of air and fuel.

Fuel Injection (FI or EFI)
A fuel injection system delivers a metered amount of fuel under high pressure into a stream of air. Unlike carburetion, fuel injection does not rely on the pumping of the engine to draw fuel into the air stream. Instead the fuel is forced through a small orifice (a fuel injector) at very high pressure. The flexibility of fuel injection systems and accuracy of fuel delivery leads to increased horsepower, better atomization of fuel, reduction in emissions, and improved fuel economy.