1800 get up and go!

[racydave]

Do'nt overlook the small things that lead to a good tune. A dial-in timing light is very usefull in determining the total ignition timing. I would shoot for a total advance around 36BTDC and go from there. Also, are the Carb secondaries working properly? And is the exhaust free-flowing? My exhaust was full of rust and junk.

[So Cal Mark]

first check the basics before attempting performance upgrades. Your car should have decent performance. Start with checking compression and cam timing, Then move on to basic tune up and carburetion function. After you've determined that all of the basics are perfect, consider upgrades

[mbouse]

100% agreement.

that little engine should be peppy, especially with the USA emission equipment gone.

getter in tip top condition with the standard things first, then look at SPENDING money on mods and upgrades.

[thechadzone]

Once you're sure you've got a well tuned stock 1800, I recommend a carburetor upgrade.

I'm pasting some good stuff from Brad Artigue's essay about fiat performance, if you email me I'm happy to send you the complete document. It is one of the best I've seen, and it'd give me a chance to give info on this board instead of getting it... For more local performance advice, I've found your mates at http://www.turbo124.com to be very knowledgable, and very cool.

-Chad

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 type of operation, the secondary category is type of cold start device.
These concepts are as follows:
Modifications that Make Sense
Carburetors (continued)
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.
Modifications that Make Sense
Carburetors (continued)
Carburetors by Type of Operation, Type of Cold Start Device
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.
ADHA and DFH carburetors are not easy to rebuild; the ADHA can still be purchased new.
Vacuum Operated Mechanically Operated
Manual Choke DFH DMSA
ADHA
DHSA
Automatic Choke ADF
ADL
ADHA
Electrical Choke DFEV
Modifications that Make Sense
Carburetors (continued)
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. Anyone can learn to install and tune a DMS carburetor.
If you intend to use the DMS on a later model car (where the throttle lever is cam-box mounted) then you
will have to order a different throttle "pull" assembly for the carb. This is easy to replace and costs about
$10.
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. Vehicles will still pass 49-state emission
control laws.
If you intend to use the ADFA on a later model car (where the throttle lever is cam-box mounted) then
you will have to use the throttle "pull" assembly from your ADHA. If you intend to use the ADFA on a pre-
1975 model year car, you will have to install the heater pipe (runs under the exhaust manifold) from a
1975+ model year Fiat 124. This heater pipe has the necessary fitting for running the ADFA’s waterheated
choke. You will then have to run coolant hoses from this heater pipe and the intake manifold to
the carburetor choke assembly.
Carburetors (continued)
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.
A great performance increase over any stock Fiat carburetor. Available new. Parts interchange with ADF
and ADL series carburetors - and these parts are easy to find and cheap. Can be used under Fiat air
cleaners, although a "free flowing" type is suggested. Vehicles will still pass 49-state emission control
laws.
The 34ADF is expensive - average price is $400 to $500, not including the Single-Plane manifold (if
needed) which average about $75. If you intend to use the ADFA on an pre-1979 model car (where the
throttle lever is manifold mounted) then you will have to use the throttle "pull" assembly from your
existing ADFA or DHSA carb. If you intend to use the ADFA on a pre-1975 model year car, you will have
to install the heater pipe (runs under the exhaust manifold) from a 1975+ model year Fiat 124.
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.
Available new (but rare!) and much easier to find in Europe than in the U.S.. The 36ADL is a remendous
performance increase over stock. To be truly effective you need to increase the compression in your
engine to at least 8.9:1 and possibly add higher lift/duration camshafts. I ran a 36ADL on a stock
compression 2 liter engine with an 1800 head and stock cams with wonderful results.
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. A wire leading from the coil to the choke works well.