what if N/A more power than turbo ?

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The Block

The block ends are resurfaced for Cosmetic Purposes, the sump is ground with a rough cut and fast machine feed rate, the surface finish this creates is ideal to seal and grip the cork gasket. When fitting the sump cork gaskets no sealant should be used with the exception of joints between the gasket ends and where the flexible plastic bows butt up to the ends of the cork gaskets, a small blob of the RTV Type sealant is applied. The cork gasket can be secured by sticking them in position with a few tacks of impact adhesive.

Crankcase Main Line
All of the five main bearing caps are lightly ground on the joint faces, the caps are fitted to the Cylinder Block and the securing bolts are torqued to the original manufacturers torque tension. The main line bore is then measured to check that sufficient stock has been ground off the joint faces to allow stock to be honed from the main line bore therefore correcting the bore diameter and most importantly the precision alignment of all 5 bearing housings resulting in a freely turning crankshaft reducing any bending stresses in the Crankshaft. The alignment is maintained to less than half a thousandths of an inch (0.0005”) the main line bore is kept to a roundness of 0.000” – 0.0003” (zero to 3 tenths of a thousandths of an inch.

Conrods
The rods and caps are precision ground on the joint faces, approx. 0.003” (thou) is ground
off the four joint faces. The caps are assembled to the rods and the conrod bolts are torqued
to the makers recommended torque tension. The big end bore is measured to ensure efficient that sufficient stock has been removed from the joint faces to allow the conrod bore to be honed to the manufacturers original size, the bore is honed on our Sunnen LB 1810 precision honing
machine. The roundness of the bore is maintained to 2 tenths if a thousandths of an inch
(0.0002”), the small end of the conrod is milled on the sides, this is done to allow the 93mm
V6 piston to be fitted to the conrod giving the correct side clearance between the inner
piston bosses and the conrod eye. Each conrod is subjected to a Magnetic Particle Luminor
NDT Crack Test. All four conrods are weighed and balanced in sets, the tolerance maintained
between each set is 0.00 – 0.5 grams.
Crankshaft
The Crankshaft is first inspected and assessed for suitability, the Crank is set up on “Vee Blocks” and checked for bend, then all the Crankpins and main bearing journals are measured to ensure the pins and journals are suitable for regrinding. The conditions of the front snout and flywheel bolthole threads are checked along with the front keyway. The Crank is set up in the Crankshaft regrinding machine, on completion of regrinding the front and rear oil seal tracks are lightly reground with the absolute minimum of metal removed, this process ensures the there is zero run out between the main bearing journals and the oil seal tracks ensuring oil seal reliability and longevity.


Crankshaft Regrinding
The rear Crankshaft flywheel mounting flange is also reground eliminating any runout and this ensures minimal flywheel face runout. On completion of the regrinding process the oil holes are lightly honed to remove any sharpness at the mouth of the holes and this also allows the lubricating oil to spread across the bearing quicker and more evenly resulting in improved bearing lubrication. All the Crankpins and main bearing journals are polished to give the correct surface finish required to ensure good bearing life. Each Crankshaft is subjected to a magnetic particle non-destructive “NDT” Crank Test where any cracks are identified under ultra violet light.
Pistons:
The pistons used in engines are propriety brand @ 93mm diameter. The are cast aluminium alloy incorporating cast in steel reinforcing struts. The cast in reinforcement plates control the expansion of the piston body and allow the piston to run with less piston to bore clearance than with traditional cast pistons therefore reducing piston noise (commonly known as slap) especially at cold start up. These reinforcing plates also stiffen the piston body increasing the strength of the piston body and reduce the risk fatigue cracks where the piston skirt joins the piston pin bosses. The piston pins are of the semi floating type and are retained by a transition fit in the eye of the conrod.
Fitting Pistons :
The Gudgeon Pins are semi floating and are retained by being a transition fit in the conrod small end eye. There are two methods of fitting the pin to the conrod, the first method is to
support the piston on a shaped bolster and press the gudgeon pin through the conrod small
end eye to the correct installed position however this is not good practice as distortion and
damage are common occurrences and if the piston becomes distorted this will probably
result in piston wear or failure. The correct method of fitting the gudgeon pins to the conrod is to use specially designed equipment. The conrod small eyes are placed in special timed heater cells and when the conrod eye is heated over a pre-determined time the conrod eye is expanded sufficiently to gently push the new gudgeon pin into position and the installing jig is adjusted to give the correct final position of the gudgeon pin, soon after the pin is in position the cold gudgeon pin quenches the hot rod eye and the fit is complete without stressing the piston.

The Dummy Build
Limits & Fits :- The Conrods are fitted to the Crankshaft out of the Cylinder Block and the
bearing running clearances are checked – ( radial clearance) using plastiguage, the conrod free end play is also measured – ( axial clearance). All the piston ring gaps are measured relative to the Cylinder they are to be fitted to. Each piston running clearance is measured relative to the Cylinder it is to be installed in. The Crankshaft is fitted to the Cylinder Block main line and
again all the main bearing running clearances are measured finally the crank end float is set up. The pistons are fitted to the conrods using special dummy gudgeon pins and these assemblies fitted to the engine.

Checking Big End Clearances
Each piston is set precisely to TDC, and the piston height in relation to the Cylinder Head Block top Deck is measured To determine the amount of stock to be removed from the Block Top Face. On completion of the bearing and piston clearances the pistons and conrods are removed and also the Crankshaft & Bearings -
Checking Ring Gaps
- the dummy gudgeon pins are also removed. The pistons, conrods & crankshaft are balanced. All components are finally inspected any final cleaning required.

The Assembly
Pistons are fitted to the conrods using special sunnen equipment, the Crank and Conrod assemblies are refitted to the Cylinder Block, each connecting rod nut is secured with a little loctite. The block ends and sump faces are lightly coated with clear lacquer. The oil seals are pressed into the plates and the rear crank seal fitted and the rear main cap is fitted
with the application of the relevant sealant. The auxiliary Jack Shaft is fitted checking
the running clearance. The front seal carriers are fitted to the block front end. At this stage the two timing belt pulleys are fitted and secured. Sealant is applied to the core plug bores and the new core plugs are fitted. A new pilot bearing is fitted to the rear crankshaft flange. Finally the Cylinder Block is painted also the conrods and pistons are stamped with the appropriate piston numbers. Each main bearing and conrod fasteners are paint spotted after final torqueing.

Big valve into cylinder head
Each Cylinder Head is dismantled completely and the casting chemically cleaned back to bare iron. A visual inspection of the casting is carried out. The Cylinder Head is crack tested in the critical areas, all threads are also checked. The valves guide bores are machined to accept special thin wall bronze valve guide inserts. These inserts are fitted into position and followed by expanding the bores of the thin wall guides by a succession of broaches being driven
through the guides and are expanded until the required gauge size is achieved resulting in the desired valve to guide clearance is attained. The Exhaust valve runs at a slightly greater clearance than the inlet valve this is required because the exhaust valve stem runs much hotter than the inlet therefore requiring more running clearance. Each Cylinder Head is fitted with special hardened exhaust valve seat inserts suitable for unleaded fuel. The Cylinder Head is set up on a specialized machine and a counterbore is machined to a precise diameter and depth. The hardened valve seat insert is then fitted to the prepared Cylinder Head. After fitting the
valve seat is profile cut to give throat, valve and clearance angles. After fitting the Valve guide and Valve seat inserts the inlet and exhaust ports are worked out to the required shapes and sizes, each combustion chamber is shaped and polished and finally each chamber is measured by using fluid and a burette and all chambers arre balanced with 0.5cc. On completion of all major metal removal the Cylinder Head casting is pressure tested to prove that the water jacket has not been ground through during the various process to remove metal from combustion chambers and ports. The head is fitted with a jig that closes off all the water ports, the head is submerged in hot water approx 80◌۫c which simulates the actual running temperature of
the Cylinder Head. The head is then charged with compressed air at approx 120psi, the charged Cylinder Head is re-submerged in the temp controlled hot tank and the casting observed for leaks. The Valves used are of high quality material EN21-4N. The inlet valve head size is 44.5mm and the exhaust head size is 38mm. The valve stems are chrome flashed to give long life and reduce wear. These valves are of Standard Length 111mm and not the long group one
length. Both Manifiold faces are machined with the minimum of stock removal. This is done to ensure these surfaces are flat and achieve a positive seal at the manifold joints. The main face is
machined with the required amount of stock removed to give the correct compression ratio. Once all the major machine work has been carried out the Cylinder Head is nearing completion and a few, final requirements are taken care of, the cam bearings are replaced using high quality bronze overlay bushes, the valve springs “although new” are checked for their spring rate. Once all the work has been completed the head and associated components are finally chemical cleaned and inspected. The casting is painted in all the external casting areas. The fitted heights of the valves and springs are checked, the new valve stem seals are fitted and the valves are sprung up. After the valves have been assembled a vacuum test is carried out on each valve via the port and this test proves that there is no leakage at the valve and seat.

carburetor [fiat] explaination x2

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carburetor [fiat] explaination x2
FIAT
Special to mirafiori
Tuning Single Carburetors
Preliminary Settings

Note: These is the recommended procedure per Weber with some modifications, you will find the same general steps in any publication on setting up carburetors.
Check Factory Settings
Do not rely on the factory settings unless otherwise directed by your vendor. Back out the idle speed screw (see figure) until it is no longer in contact with the throttle stop lever. Now turn the screw until it contacts the lever and again 1 ½ turns. Turn the idle mixture screw (on our carburetors it is typically in the center bottom of the carburetor body) in until it is fully seated - do not force the screw. Now turn it back out two full turns.
Start and warm the Engine
Disengage or block the choke open. On automatic chokes you can use a small clamp or wire to pull the choke mechanism open. The engine should start and run poorly (if it does not then increase the idle speed screw ½ turn until it does). Adjust the idle speed screw until the engine runs at approximately 900 RPM. Turn the mixture screw in (lean the mixture). If the engine increases in speed then continue to turn until it is no longer increasing or runs worse, then back the screw out ½ turn. If the engine decreases in speed then turn the screw out until it is increasing in speed. Continue to turn until it is no longer increasing or runs worse, then turn the screw in ½ turn. Adjust the idle to approximately 850 RPM. Let the engine warm up to operational temperature. On a Spider you will wait until the fan has cycled two times (on-off-on-off).
Final Settings
Note: should the engine fan come on during these steps STOP working until it shuts off. Set the idle speed screw so that the engine runs at 850 RPM, or 900 RPM if you have air conditioning. Recheck the mixture screw by turning slightly in then out. Engine speed should be set - using the mixture screw ONLY - to the fastest and smoothest point of operation (listen for exhaust popping). Reset the idle speed screw as necessary.

The Mystique
Dual Webers are just plain neat to work on, look at, and operate. They are loud, powerful, and demonstrate your ability to really tackle carburetion. Many FIAT owners consider installing twin Webers on their FIAT engine, and many have taken the plunge.
Dual Carburetor Configurations
There are configurations that you should consider if you want to work with twin carburetors. They are both Weber products, Solex and Dellorto configurations are not listed because they are not available new and parts can be nearly impossible to find. These carburetors are downdraft, two-barrel, synchronous operating units. Each barrel is fully independent of the other and can be tuned as such. Barrels share only the fuel bowl and accelerator pump. They require special manifolds to work - manifolds without plenums, so each cylinder has a unique runner to its own carburetor barrel. The two models used on FIATs are the Weber IDF and DCNF. The Weber IDF is available in 40, 44, and 48mm configurations.

Dual Carburetors
The second popular configuration is the Weber DCNF, available in 40 and 44mm sizes. The 40DCNF is a more compact and modern design, but the operational principles are the same as the IDF. Generally speaking, a set of DCNFs will cost more because the manifolds are a bit more expensive. However, the manifolds are also a bit higher in quality and design than the IDF manifolds. Ultimately, the choice is yours. FIAT used IDFs so many people choose those. I have used both and have been very pleased with them.
How much power will I get?
About 25% more than a stock single carb, which is very restrictive. You are literally doubling the venture area when you go to dual carbs over stock. Compared to fuel injection, the picture is muddier, since stock specs show that FI adds 20% to the twin cam.
Are they hard to keep in tune?
Opinions vary - Mike Richmond (who wrote the majority of this appendix) says Not if you stick with a “tried and true formula: set them up and tune them. Then leave them alone. Replace the needle/seat and clean them every 24,000 miles.” My experience has been that they are generally seasonal, at least in Atlanta I found myself jetting up or down (just the idle jets, mind you) four times a year. Easy work.
Are they hard to tune the first time?
They shouldn’t be, but most people make the mistake of failing to install them right the first time (especially used ones) or they change too many things at once. Install them right and be scientific and you will have them humming after a couple of weekends. In the meantime, you will learn to curse in Italian. You absolutely need a device to measure the amount of air drawn into the carburetor barrels (available from most vendors or carburetor shops) to tune these carburetors correctly. This device measures the amount of airflow into each barrel. The preferred unit is the Type SK (vs. the Type BK) Synchrometer with adapter number 18. This will fit nicely into the ram pipes (velocity stacks) of the IDF 13/15s. The Uni- Syn gauge (another type of metering device) is not recommended for tuning IDFs. A fourth type is available from most motorcycle shops and has four gauges which each attach to the vacuum port at the base each carburetor (next to the air bleed screw). I refer to ALL of these devices as in the next topic.
Quick Tuning Guide
First, reset the carburetor to its basic settings. Turn in all four air bleed screws until they are seated. Screw in all four mixture screws until they seat, then back out 1 ½ turns. Adjust the idle stop screw (between the carburetors) so that the engine idles (even if poorly) around 900 RPM. Balance the airflow between barrels using the synchrometer. First measure the air in both barrels of a single carburetor. Adjust the one with the lowest reading to match the one with the highest reading by adjusting the air bleed screw. Repeat for the other carburetor. Now compare the airflow on one carburetor to the other and balance them using the center link balancing screw. Set the mixture by turning the mixture screws - one at a time. First turn the screw in, if the engine speed begins to increase keep turning until the speed begins to decrease or run worse then back ½ turn. If the engine speed begins to decrease reverse this operation, turn the screw out and speed will increase, turn until it begins to decrease or run worse then in ½ turn. Fine tune as necessary using similar steps. These are finesse carburetors, you master them in a very short amount of time!
# if you to get FIAT WEBER carburetor manual click this: FIAT WEBER MANUAL

carburetor [fiat] explaination

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special thanks to mirafiori
FIAT
• Introduction
• What's in Your Car
• Performance
• The Baseline
• Exhaust Systems
• Tuning Single Carburetors
• Dual Carburetors
• Weber IDF Diagrams
• Weber ADF / ADFA
• Weber ADHA
• Weber DFH
• Weber DMS / DMSA
• Identify the components that are actually installed in your FIAT.
• Define performance in terms that make sense and prepare for modifications
• that suit your performance needs.
• Establish a baseline of how your car performs with the current equipment.
• Determine if you need to alter the existing configuration or simply fix what
• you have.
• FIAT installed a variety of exhausts on their vehicles. Some systems are
• quite good, others are restrictive.
• A reference on how to reset and tune a single carburetor
• Installing Dual Webers can be a real kick in the pants. This section deals
• with the Weber IDF series.
• Intake and Carburetion
• FIAT installed a variety of exhausts on their vehicles. Some systems are
• quite good, others are restrictive.
INTRODUCTION
FIAT used Weber as the primary source of carburetors throughout the 60's and 70's. Factory changes in carburetor types occured during engine displacement upgrades, changes in regional laws (such as environment legislation), or during model year changes. Most owners can be fully confident that the carburetor on their FIAT has been modified, replaced, rebuilt, or swapped for another model. The engines are flexible enough so that virtually all FIAT-Webbers can be easily adapted fit on any model year vehicle. This interchangeability makes it easy to find the right carburetor to suit your needs. 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. 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 reduction for almost 20 years), and is really a compilation of years of work enjoying these fine cars. The first edition focused on the carburetion, intake, and exhaust system. That work has been expanded and now includes schematics for the various carburetor types. A new guide is also available for Fuel Injected Spiders. This guide is freely distributable in electronic format provided it is distributed in the original form. Images are scanned with 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.
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.
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.
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.
Exhaust System Identification
Identifying your exhaust system is actually quite easy - there are no numbers or charts to compare and all you really have to do is look in your engine compartment. FIAT used two basic system designs on carbureted engines. The first design is traditionally called the “4-1” or “four into one” system. The second is known as the “4-2-1” type. Look in your engine compartment at the exhaust side of the engine. There may be a metal heat shield on top of the exhaust; it will have three 13mm nuts securing it down. If you cannot see under the shield you may need to remove it (with the engine cold!) to see what you have. The 4-1 type will have four short pipes, one from each cylinder, terminating into a single large pipe those routes under the car. The 4-2-1 type has a 4 into 2 cast manifold. A steel downpipe connects to the manifold and merges (collects) the two pipes into a single pipe those routes underneath the car. There are two types of the 4-2- 1 manifold. The first type has a small collector and does not have an oxygen sensor socket. This was the standard type for carbureted engines. Some owners of the 1979/80 cars have installed the fuel injected type 4-2-1 system. It can be identified by a large collector with an oxygen sensor socket. This second type is often used because it fits the 2000cc engine better than the older 4-2-1 design.
Intake Manifold Identification
FIAT used two basic types of intake manifolds on carbureted engines. Although there are identifying numbers on the castings, no reference has been made available that accurately categorizes them. The easiest way to identify what you have is to remove the carburetor and look at where it bolts down. If there is a single hole and a large chamber then you have a “single plane” manifold. If there are two distinct sections, one for the primary barrel and one for the secondary, you have a “dual plane” manifold. Identification without removing the carburetor is more challenging. The Spider 2000 - 1979 and 1980 - has the largest manifold and it is nearly flat on top. It has a “waffle” pattern cast into it and several ports for emission control equipment. It is very angular in appearance. The Spider 1800 has a more simplistic manifold with four pipes (one per cylinder) and space between the pipes. It is much more curved in appearance. 1800’s have a “Christmas tree” of ports on the front. The Spider 1608 and 1592 manifolds are very similar to the 1800 but typically have only a port (for the brake booster). Spider 1438 manifolds are not interchangeable with other cylinder heads because they lack the coolant passage rearward of the #4 intake runner.
What is Performance?
Performance is a relative term. You need to define how you want your engine to perform so that it suits your needs. A high performance engine is not necessarily fast and a poorly performing engine is not always slow. Look at it this way: I used to own a FIAT 850 Spider, with a 903cc engine that produced around 62 horsepower. It was a rebuilt block, all bored out and with a nice polished cylinder head. It had a carburetor upgrade and a nice exhaust system. In terms of performance it was a How? First, it surpassed my expectations in terms of how smoothly it operated. Second, it got better fuel economy than I ever expected. Third, it produced more horsepower than I projected. I was getting 62 HP from a 903cc engine with a tiny carburetor and antique cylinder head design! Relative to my expectations (I expected it to perform well) it was a high performance engine. Now look at it another way: Lots of car companies state that their engines are “high performance” just because they produce more than “x” horsepower or “y” torque. But look at what these companies do to produce this power - enormous V6 and V8 engines that barely produce ¾ of a horsepower per inch of engine displacement. You have 350 and 400 cu. in engines producing fewer than 300 HP. Alfa Romeo and FIAT was producing 1HP per cubic inch of displacement in the 1960’s. Sure, the engines produced around 100 to 120HP, but which one is higher performance? It's up to you to define performance in terms of what you want your car to do. Judge for yourself. Do you want to build a 200HP Spider? It can be done, with a standard FIAT engine block, cylinder head modifications, high compression pistons, lightened flywheel and connected rods, supercharging, etc. Do you want a (slightly less expensive) 100 to 120HP Spider that gets good gas mileage, has few mechanical problems, and can last for 50 to 100,000 miles? Most of us desire the latter, a car that you start in the morning, drive all day (even in traffic), and enjoy. Underneath the hood of your Spider is an engine that was designed to perform efficiently and reliably. If someone contradicts this, they are not aware of the potential of the FIAT DOHC design. Without getting into a history lesson, FIAT’s belt-driven DOHC configuration has been duplicated by most other auto manufacturers. It is elegantly simple and wonderfully effective. And, unlike most engines made today, can work on it in your garage with minimal expense.
BASELINE
Using the information you’ve already gathered (engine type, head type, etc.) you are already on your way to establishing a baseline for your engine’s performance. The recommendations in this section are optional, but you really should get a feel for how your existing setup operates before trying to change anything. Things to check/replace prior to getting started with any modification:
1. Ignition system: as necessary, new plugs, wires, distributor cap, rotor, vacuum advance capsule and hose, coil, pickup, points, condenser, points gap, dwell setting. Set the ignition timing to exactly what your car’s instruction book calls for. If you have Marelli electronic ignition (1979-1985) be sure the vacuum advance is working properly.
2. Valve lash: make sure the valve lash is within specification.
3. Coolant: make sure the cooling system is properly filled.
4. Oil: FIAT recommends 15W40 oil and a new filter with every oil change.
5. Gas: Fill up with the highest octane you can get from the pump. Do not baseline your engine with fuel additives - use a fresh tank of gasoline (and nothing else).
6. Carburetor: Clean it and lubricate the mechanicals with 3-in-1 oil.
7. Fuel filter: Use a new filter or replace with a clear filter.
Why do I recommend you do all of these things? You are getting ready to make changes to how the engine breathes. Prior to doing that you have to know exactly how it operates in its current state. In other words, you cannot intelligently move from point “A” to point “B” when you don’t know what “A” really is. And if any of the five things above have not been attended to in a while, you’ve lost track of what “A” really is anyway. Once you’ve done the things above, drive the car and make observations. How fast is the car from 0 to 60 MPH? How responsive is the throttle? How good is your gas mileage? Does the car do bad things, like foul spark plugs, start poorly on cold days, etc? At the point where you are completely comfortable with the current operating condition of your car, ask yourself: is it good enough? If you are happy with the speed of the car, happy with the way everything works, do you really want to start changing things? If not then don’t be ashamed, enjoy your car. If you do want to make some changes then keep reading about the different options you have available to you.
EXHAHUST SYSTEM
There are roughly two options when discussing the pipes from the engine to the catalytic convertor (or at least under the car if you have no catalytic convertor):
1. Install (or continue using) a FIAT 4-2-1 exhaust system, replacing the 4-1 exhaust that you already have. This results in better flow and much better high end performance. Frankly, it also sounds better.
2. Install a custom-made header. These are typically four long runners into a single collector and are made of thin steel. They are louder than an iron stock exhaust and many people swear by them. I have not personally found them to be any more efficient than the stock 4-2-1 system.
Underneath the car you may or may not have a catalytic convertor. If you do (and if it is old) consider replacing it with a free flowing unit. These units use a platinum honeycomb core rather than stones to do their job. They are more efficient and help you obtain more power. Behind the catalytic convertor is a center resonator, located just in front of the axle. Three options are available: the stock type, a “performance” type, and a straight pipe. The stock type of resonator is adequate for nearly any kind of street use. It is typically manufactured by ANSA (or TESH, the same company) and is around $75. These tend to rust so check yours and replace if necessary. The performance type is, unfortunately for those who buy them, basically the exact same thing with a black powder coating. Many vendors do not stock them for this reason. The third option, a straight pipe, results in a different exhaust note. The exhaust “tip” (the part that sticks out under your rear bumper) is available in stock and performance versions as well. You can also get various types of straight pipes, trumpets, etc. The stock ANSA/TESH rear section is more than adequate for street use, is generally well made, and hangs properly under the car. My experience with the twin-tip “performance” exhausts is that they result in a louder (some say “throaty”) exhaust note but do not improve performance. You may have to modify early Spiders to accommodate the twin-tip style muffler. If nothing else, consider them a cosmetic change. Other types of tips (certainly the “trumpet”) are much louder and less restrictive, but keep in mind that ALL of these designs are generally unrestrictive and well suited for street use. I believe that everyone should run a 4-2-1 front section or performance header, a honeycomb type catalytic convertor (if necessary), a stock center resonator, and stock rear section. These components provide admirable service for street use and do not impair the performance of a good street engine.
INTAKE AND CARBURETION
Intake Manifold
As discussed earlier, there are two basic types of intake manifolds. A single plane manifold is essentially a plenum chamber in which both carburetor barrels add to the mixture. A dual plane manifold separates the barrels into two plenums and then independently into each intake runner. The single-plane type is necessary for any carburetor with a mechanical secondary; the dual-plane is typically used when the carburetor has a vacuum-operated secondary. These concepts are explained in the next topic. The ideal intake manifold is the one used on the 1756cc engines. It is a fairly compact single-plane manifold with few ports (so you need to do less work blocking these ports off). It will fit on every DOHC cylinder head and fit all of the Weber carburetors described in this document. If your stock carburetor was installed on a dual-plane manifold and you intend to retain that carburetor, continue to use the stock dual-plane manifold. The most obvious example is the Spider 2000 (1979 and 1980 carbureted models) with the Weber ADHA and dual-plane manifold. These components were designed to function together. The ADHA on any other manifold performs poorly; any other carburetor on the 2000 manifold is restricted in its efficiency.
Carburetors
Carburetors are the most likely reason you are reading this document. Over the next few pages we will discuss the types of carburetors FIAT used and which one will be the best fit for your car. You’ve already done the work in identifying which carburetor you have on your car. The chart presented in this topic will educate you in the basic operation of the carburetor and if you should consider swapping it out for another unit. Also discussed in this section are the true upgrade carburetors, selected by FIAT or FIAT vendors as suitable for use on our engines. Because they are available brand new they may be a great option for those of us not wanted to rebuild an old carburetor. The chart on in this section splits carburetors into two primary categories and then into secondary categories. The primary category is , the secondary category is . These concepts are as follows:
Type of Operation: Vacuum or Mechanical.
A vacuum operated carburetor uses intake manifold pressure to open the secondary barrel at a specific point in time. For example, the Weber ADHA carburetor is designed to begin opening the secondary barrel at around 3500 RPM under a running load. A mechanical carburetor uses two gears or a lever system to always open the secondary barrel when the primary barrel is at a certain angle. The advantage of a mechanical secondary is obvious: regardless of engine speed and load you can deliver more air and fuel to the engine as you require it. The result is much better acceleration, better passing ability, and better throttle response. The carburetor acts exactly as your foot requires. A vacuum operated secondary will not act in such a fashion. At rest you can often completely depress the gas pedal and redline the engine without the secondary ever opening -- all because the engine (at rest) doesn’t generate enough pressure to pull open the secondary. It is a more fuel-efficient design and is a good bit smoother during transition to the secondary barrel.
Type of Cold Start Device: Manual, Automatic, Electrical
A cold start device is known as a “choke” to us Americans. It is typically a flap of metal over the primary carburetor barrel that restricts the flow of air (resulting in a rich mixture). It is necessary for cold mornings when fuel doesn’t want to atomize. A manual choke is operated by a cable-and-knob with the driver pulling the knob out to engage the choke or in to disengage. 1960’s and most 1970’s Spiders have mechanical chokes. An automatic choke is operated by routing coolant into a special chamber on the carburetor. Inside the chamber is a spring that expands when hot. As it heats up the choke flap begins to close. Prior to starting the car the driver will fully depress the accelerator and release it, thus setting the choke. Operation is then automatic. An electrical choke has a temperature sensor that operates in place of the coolant mentioned above. More elegant in operation, the driver does nothing but start the engine. The choke engages automatically and all operation is also automatic.
Vacuum-Operated Carburetors: The DFH, DHSA, and ADHA.
The DHSA and DHSA2
The DHSA was installed on the original 124's up to 1971. Difficult to find parts for and generally notorious for secondary vacuum leaks, the DHSA is not a popular upgrade nor is it recommended as a candidate for a rebuild. The DHSA2 and later models were used from 1971 through 1973 and offered larger primary and secondary barrels. Difficult to find parts for and often hard to rebuild correctly, unless absolute originality is required, this carb should be removed and replaced with a later, mechanically-operated model. It is difficult to find parts for the DHSA series, although the vacuum operated secondary diaphragm can still be had new. Rebuild kits are also available but some of the items are simply impossible to find.
The ADHA and DFH
The ADHA was installed on 1979 and 1980 49-State Spiders (or those not imported into California). The DFH is rare, used on very early Spiders. Both operate using a large vacuum operated secondary located near the secondary barrel. The ADHA has a tiny 28mm primary barrel and a 32mm secondary barrel. It is designed for emissions control and not performance and is to blame for much of the 1979/80 Spider’s sluggish operation.
Mechanical Carburetors with Manual Chokes: DMS.
The 34DMS / DMSA
The DMS/DMSA series was, and still is, extremely popular. Inexpensive, even when purchased new, a DMS carburetor will bolt right on to your Fiat, link up, and run. It has a mechanically operated secondary and choke, and even the DMSA has few emissions control provisions. The DMS can be an impressive performance increase over stock DHSA and DFH carburetors, and retains fuel economy. You can retain the originality of the mechanical choke yet gain a good amount of performance (the DMS is a more powerful carb than a DHSA). It will also fit under one of the stock Fiat air cleaners if you intend to do so.
Mechanical Carburetors with Automatic Chokes: ADF, ADFA, ADL.
The 32ADFA
The 32ADFA is probably the most prevalent Fiat Spider carburetor on the "used carbs" circuit. Large, wellbuilt, and reliable, the 32ADFA bolts right up to the Single-Plane manifold (used on the 1756cc cars) and can therefore be installed (with the manifold) on any Fiat 124. It has a mechanically operated secondary and automatic choke, and like the DMSA has few emissions control provisions. Impressive performance increase for DFH, DHSA, and ADHA owners - and retains fuel economy. Automatic choke retains originality for stock and later model cars. Also fits under stock Fiat air cleaners for those wishing to maintain originality. A great performance increase for all Spiders not originally equipped with the ADFA, including the 1979 and 1980 cars.
The 32ADFA
The 32ADFA is probably the most prevalent Fiat Spider carburetor on the "used carbs" circuit. Large, wellbuilt, and reliable, the 32ADFA bolts right up to the Single-Plane manifold (used on the 1756cc cars) and can therefore be installed (with the manifold) on any Fiat 124. It has a mechanically operated secondary and automatic choke, and like the DMSA has few emissions control provisions. Impressive performance increase for DFH, DHSA, and ADHA owners - and retains fuel economy. Automatic choke retains originality for stock and later model cars. Also fits under stock Fiat air cleaners for those wishing to maintain originality. A great performance increase for all Spiders not originally equipped with the ADFA, including the 1979 and 1980 cars.
The 34ADF
One of the best carburetors made for the 124. Solid and extremely reliable, the 34ADF was provided (by Fiat, actually) as a bolt-on performance improvement for 1975+ Fiats. Nearly identical in manufacture to the 32ADFA, the 34ADF lacks the emissions control ports of the ADFA and has larger primary and secondary barrels, improving performance throughout the entire r.p.m. range. Requires the Single-Plane manifold to operate efficiently. Has an automatic choke.
The 36ADL and 38ADL
Similar to the ADF series in most respects, the ADL was designed for the Lancia Gamma 1995cc and 2800cc cars (neither of which were sold in the U.S.A.) Hard to find, the ADL series can add serious performance where a single-carb is required. ADL carburetors, like the ADF, have a water-activated automatic choke.

Mechanical Carburetors with Electrical Chokes
The DFEV
Our deviant from the manual/water choke fold is the electric choke DFEV, available new from parts vendors and with two huge barrels. A more modern design than the ADL or ADF, the DFEV offers the same basic benefits (and the same difficulties when mounting to a pre-1979 engine). Note that the DFEV requires a positive lead (energized by the ignition key) to operate the electric choke.
Which carburetor should you run?
For Spiders currently fitted with DHSA, or DFH
For DHSA and DFH owners, purchase an 1756cc intake manifold. Remove from it (and block off) all ports except the brake booster pipe. For those who already have the 1756cc manifold, remove it and block off same. Install a 34DMS carburetor. It will work with your existing linkage and choke mechanism and provide an instant power and reliability increase.
For Spiders currently fitted with ADFA Carburetors
For those who already have the 1756cc manifold, remove it and block off same. Consider purchasing a Weber 34ADF. If the cost is prohibitive then consider rebuilding or replacing the 32ADFA you already have. The 32ADFA is no slouch and if it is in good condition can perform admirably. Early ADFA Spiders may have a lever type throttle assembly, the 34ADF may have to be modified to operate it (consult with your vendor).
For Spiders currently fitted with DHSA and DFH Carburetors.
Purchase an 1756cc intake manifold. Remove from it (and block off) all ports except the brake booster pipe. Install a 34DMS carburetor from an a 1974 Spider. These carburetors were available new just a few years ago but may be hard to find today; your best bet may be finding a used Spider or other vehicle fitted with the 34DMS. It will work with your existing linkage and choke mechanism and provide an instant power and reliability increase. Depending on engine displacement you may have to decrease the main jet and idle jet sizes.
For Spiders currently fitted with ADHA Carburetors.
Purchase an 1756cc intake manifold. Remove from it (and block off) all ports except the brake booster pipe. Purchase a Weber 32ADFA and install it. The 32ADFA will bolt right up - install your choke hoses and vacuum advance and away you go! It will require increasing the size of the main and idle jets by 5 - in other words, if your idle jet is currently 55 you should go with a 60. But TRY the 55 first. Also consider the 34ADF on the 1756cc intake manifold. It's a great compliment to the 2000cc engine. Note that not all 34ADFs have the vacuum port for the distributor advance. If you run the stock ignition system then you need this port - ask for it or have it drilled by an experienced carburetor shop.

Cylinder Heads
The cylinder head on your car is likely the correct one for the model year. In most cases (1438cc, 1608cc, 1756cc, 1592cc) I say to stick with your existing cylinder head. But the 1995cc (2000 Spider) engines can benefit from the slightly smaller combustion chambers of the 1756cc cylinder head. The smaller combustion chambers result in increased compression - desirable for performance. From “seat of the pants” observations made by myself and many others who have performed this modification, you can expect better acceleration and better performance at high speeds. Best yet, there is no magic to doing it - if you can replace the head gasket then you can replace the cylinder head. Your existing 1995cc cam boxes, wheels, valves, etc. will all fit perfectly. Porting and polishing are techniques that your machine shop can assist you with. Getting the ports and chambers opened up (ported) and shiny (polished) results in better airflow throughout the cylinder head. Better airflow=more power.