tuning-fiat-engines.pdf

Intake, Combustion, and Exhaust Modifications

First Edition - November 2001

Brad Artigue

Contents

Introduction

What’s on Your Car?

Understanding Performance

Establishing a Baseline

Modifications that Make Sense

Tuning Your Carburetor

Appendix: Dual Weber Carburetors

Credits etc.

Special thanks go to Thad Kirk and Pete Angel for contributing to and

proofreading this document. Both are FIAT experts - Thad Kirk is

thadkirk@hotmail.com, Pete Angel is pete@mirafiori.com.

Thanks to Troy McKaskle (troymckaskle23@hotmail.com) for

proofreading and allowing me to work on his 32ADFA and 40IDF

carburetors time and time again.

To Mike Richmond (msrichmond@aol.com), who started working with

Weber IDFs about the same time I did and is an author of the

appendix.

To everyone on Mirafiori (www.mirafiori.com) who ever mentioned

the word “help” and “carburetor” in the same sentence. Your

thoughts motivated me to work on these carbs.

Diagrams in this document were scanned with permission from the

FIAT Spider Service Manual. This document is not intended for profit

but for education, distribute it to anyone who needs the information.

Should you have questions or comments or note typographical errors

please send me an email - brad_artigue@hotmail.com.

Introduction

If you own a FIAT Spider then you own a wonderful car. Superb

handling, beautiful styling, easy to work on, and inexpensive to

own, Spiders are a hobbyists’ dream. I have owned several

Spiders in the previous decade, all but one were carbureted.

During the time that I was restoring each of these cars I did a lot

of work with various carburetors and manifolds, trying to get as

much performance as possible from “off the shelf” FIAT parts.

Author’s 1980 Spider 2000

The results of this work are published in this document. It is an

unofficial document, FIAT no longer really supports the Spider (it

has been out of production for almost 20 years), and is really a

compilation of years of work enjoying these fine cars.

This document is intended to explain the various carburetion systems used by FIAT on many FIAT and

Lancia vehicles sold between 1966 and 1981. The most popular (and abundant) of these vehicles was

the Fiat 124 Spider, but many other cars shared the same engine and carburetion systems. My personal

experience is with the 124 Spider but the information in this document most likely includes your vehicle if

it says “FIAT” or “LANCIA” on the outside and there is a belt-driven twin cam engine with a carburetor on

the inside.

FIAT used Weber as the primary source of carburetors throughout the 60's and 70's. Underneath the

hood of your FIAT is most likely a dual-barrel progressive downdraft carburetor (these terms are

explained later). If your car is truly a European specification then you might have two dual-barrel

synchronous downdraft carburetors. You may also have Solex carburetors or Dellorto depending on

which manufacturer was on strike when your car was assembled.

If the above paragraph confused you, don't let it. In the next section you will identify just what you have

on your car (because it may not be the original). In the third section we will discuss what you might need

(vs. what you might think you need). The fourth section covers selecting the right manifold and

carburetor, and the fifth and final section discusses tuning your Webers for optimum performance.

Be forewarned: if you intend to run a set of Solex, Dell'Orto, or some other setup then this document

won't be much help. This document speaks specifically of Weber carburetors on FIAT engines!

For Additional Information

As you read through this document and begin to work on your car, you may want to check out the

following online resources:

www.mirafiori.com - The FIAT Page - Includes an indispensable and lively owner’s forum.

www.fiatspider.com - Also includes an owner’s forum and gallery of member cars.

www.flu.org - FIAT/Lancia Unlimited - The FIAT and Lancia owner’s club

What’s On Your Car?

It is important to know what engine, cylinder head, carburetor, intake manifold, and exhaust system you

have on your FIAT. Understanding what you have allows you to make an educated decision about what

you need. If you are not 100% sure of what you have then take a few moments to check - many a

Spiders with “2000” badges have 1800 engines and vice-versa.

Engine Identification

The engine identification number is stamped into the engine block near the oil filter. It is sometimes

covered in grime, carburetor cleaner or degreaser and a brush will allow you to read it. On the Spider

2000 engine (1979-1985) it is located just to the right of the oil filter. On all Spiders manufactured prior

to 1979 it is located above the oil filter.

Check your engine number with the chart on this page. Chances are you will have the correct engine in

your car. It is important to note that the last few numbers may not match up - this usually indicates an

engine swap at some point in your car’s history. Never fear - if the first digits are correct then you have

the correct size engine in your car.

124 Model Series From S/N Engine Displacement

Spider 1968 124AS 0005619 124AC.040 1438cc

Spider 1969 124AS 0010554 124AC.040 1438cc

Spider 1970 124BS 0021861 124AC.040 1438cc

Spider 1971 124BS 0022589 124AC.040 1438cc

Spider 1971 124BS1 0033950 125BC.040 1608cc

Spider 1972 124BS1 0047032 125BC.040 1608cc

Spider 1973 124CS 0059592 125BC.040 1608cc

Spider 1973 124CS 0063308 132AC.040.3 1592cc

Spider 1974 124CS1 0071650 132A1.040.4 1756cc

Spider 1975 124CS1 0088792 132A1.040.5 1756cc

Spider 1975 124CS1 132A1.031.5 1756cc

Spider 1976 124CS1 0099909 132A1.040.5 1756cc

Spider 1976 124CS1 132A1.031.5 1756cc

Spider 1977 124CS1 0113343 132A1.040.5 1756cc

Spider 1977 124CS1 132A1.031.5 1756cc

Spider 1978 124CS1 0126001 132A1.040.5 1756cc

Spider 1978 124CS1 132A1.031.5 1756cc

Spider 1979 124CS2 0142649 132C2.040 1995cc

Spider 1979 124CS2 132C2.031 1995cc

Spider 1980 124CS2 0157654 132C3.040

1995cc

What’s On Your Car?

Cylinder Head Identification

Cast into the top of your cylinder head is an embossed identification number. Because it is possible (and

oftentimes desirable) to install an earlier cylinder head on some blocks, you need to identify if such a

swap has occured on your engine.

Casting Number

Other Casting ID

Original Engine Displacement

Comments

4166393

124AC

1438

1968 124 Spider

4198994

124AC

1438

1969 124 Spider

4232871

124AC.000

1608

Sport Spider

4232974

124AC.000

1608

1972 124 Coupe

4238527

132AB.1A.0

1592

Sport Spider

4239436

124AC.000

1608

124 Coupe

4239436

124AC.000

1608

124 Coupe

4268803

124AC.000

1608

1972-73 Sport Spider

4277590

132AB.9A

1756

1974-76 Coupe, Spider

4304781

132AC.OC

1592

1973-1974 Spider

4314402

1756

Late 124 Spider

4325215

1995

131

4326319

124AC

1608

Early 124

4348553

134AC.6C

1756

Lancia Scorpion

4371507

132.C8.1A0

1592, 1756, 1995

131/132 and 1981-82 Spider

4372281

1995

1980 Lancia Beta

4372291

134AS

1756, 1995

1977 Spider

4372297

1592, 1995

131

4372748

1995

131

4406111

132AC.2C

1995

1979 131 & Beta Coupe

4439644

132AC.2C

1995

79 Carb Brava

5992129

1995

1984 Spider

What if your casting number is not on this chart? Do not be alarmed, this chart is a work in progress and

its contents are maintained by Pete Angel. Send him your engine displacement and casting number via

email: pete@mirafiori.com. Include as much of the casting number as possible along with the year and

model of the vehicle.

Carburetor Identification

Weber stamped an dentification number on your carburetor body. Depending on the construction of the

carburetor body, this number may stamped between the middle and lower halves of the carburetor, or on

the lowest mounting flange on the intake side. It may in a different location altogether but should be

fairly easy to spot. The number may be quite long, but the primary information is in the first few

alphanumerics.

For example: 28/32 ADHA 1/100 or 32ADFA5 1/105

The important thing to note is the numbers before the letters and the letters themselves. If you read

“ 28/32 ADHA 1/100 ” then you can simply note that you have a “ 28/32 ADHA ”.

Using the chart on the next page, note whether or not your carburetor was original equipment on your

engine. Carburetor swaps are extremely easy on FIATs and are the focus of much of this document!

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