Autolite Carburetors – Q&A

Classic Inlines offers rebuilt 1100-1V carburetors which are re-calibrated to eliminate the problems commonly found in factory calibrated carburetors, such as hesitation and/or flat spots. We currently have a fairly large inventory of 1V carbs in stock, which are rebuilt and ready to ship, however we’re always looking for more cores. If you happen to have one (or several) that your not using, please let us know. We’d be more than happy to buy them, as long as the cores are complete (no missing parts) and in reasonably good condition. Please don’t send cores that have been laying outside in the dirt for the past twenty years. You know, the ones that are pitted so bad, they look more like a moon rock, rather than a carb.

Why do Autolite Carbs require less maintenance?
Why are Autolite Carbs safer to use?
Why should I buy an Autolite carburetor from Classic Inlines?
Is bigger really better, or a myth?
How does the choke system work?
Do I need really a choke?
What is an Automatic Hot Air Choke?
How does a Manual Choke work?
How does an Electric Choke work?
What is the difference between the 65-67 and the ’68 Autolite 1100 carb?
What is Annular Fuel Discharge?
What is the formula to calculate CFM?
Adjusting a new or rebuilt carburetor?
What sizes are available in the 1100-1V and 2100-2V series carbs?



1) Why do Autolite Carbs require less maintenance?
Autolite carburetors will virtually run forever, or at least until dirt gets into the carb. Due to the one piece base, there are no gaskets to dry out, crack, and/or more importantly, leak. Not only does this result in lower maintenance, it greatly improves fire safety, especially when the carb is sitting directly over the exhaust manifold or header, as is the case with our inline sixes.

2) Why are Autolite Carbs safer to use?

See answer #1

3) Why should I buy an Autolite carburetor from Classic Inlines?
Our rebuilt carburetors are completely disassembled, including the throttle shaft and choke assembly, then soaked, media blasted, polished and/or re-plated when necessary. Once the parts have been thoroughly cleaned and inspected, the carbs are re-assembled using the highest quality kits available. Finally, the carburetors are re-calibrated and adjusted to overcome the inherent problems that were common with the factory OEM carbs, such as hesitations, flat spots under acceleration, and hard starting. Our rebuilt carbs come with a new manifold gasket, a phenolic spacer, timing & installation instructions, and a one-year warranty (from date of shipment).

Note: Click here for installation instructions for your rebuilt 1100-1V Autolite carburetor.

4) Is bigger really better, or a myth?
For years, people have had the notion that “bigger is better”. That concept is simply not true. When an oversized carburetor is installed, low end performance suffers without any appreciable gain in top end performance. An oversized carburetor will run “lean” off idle through the normal range operating range and then dump too much fuel at the top end, and run “rich”. On the other hand, a correctly sized (and functioning) carburetor will provide a constant air/fuel ratio through most of the operating range.

The idea is to choose a main body with a large enough bore and venturi area to allow maximum airflow through the carburetor, based on the engines requirements. At the same time, the venturi must be properly sized (small enough) to promote a high-speed airflow signal to the carburetor. This signal is a measurement of air speed that the carburetor reads in order to determine how much fuel to deliver into the incoming air stream. In theory, if the bore and venturi are too large, the signal will be weak at low engine speeds and the fuel will not be pulled from the carburetor’s discharge ports accurately. The opposite of this effect is when the carburetor’s bore and venturi are too small for the engine’s airflow demands. While throttle response will be outstanding, the engine’s maximum airflow, or power potential, is diminished. The ideal carburetor is large enough to move the maximum amount of airflow through the carburetor, yet small enough to maintain the strongest possible airflow signal.

Therefore, it is very important to use a CFM calculator, thus ensuring you have selected the proper size carburetor for your CFM requirements. However, it should also be noted that the calculated results are just that, calculated. Once you have done the calculations, consider the following “Rules of Thumb” before you make your final decision. Just remember, it’s always better to start small.

Rule of Thumb
Bigger Carb
Smaller Carb
More Horsepower
More Torque
Higher RPM Range
Lower RPM Range
Higher Compression Ratio
Low Compression Ratio
Higher Rear Gear Ratio
Lower Rear Gear Ratio
Lighter Vehicle Weight
Heavier Vehicle Weight
Not Enough Cam Duration
Too Much Cam Duration
Manual Transmission
Automatic Transmission
High Stall Converter
Low Stall Converter
More Mechanical Adv.
Less Mechanical Adv.

5) How does the choke system work?
When the engine is cold (at ambient air temperature), press the gas pedal all the way to the floor to close the choke plate. This reduces air flow and richens up the A/F mixture for starting. Next, pump the gas pedal once or twice, to provide the initial charge of fuel required to start the engine, then hold the gas pedal down about half way. Once the engine starts, the choke unloader will automatically open the choke plate about 1/8”, providing a slight increase in air flow, there-by leaning out the mixture. From there, the air flow requirements continue to increase as the engine heats up, eventually requiring the choke plate to be in a fully opened position. This is done either manually or automatically, depending on the type of choke mechanism used on the carb. A manual choke requires the driver to open the choke plate by means of a choke cable, whereas an automatic choke does it automatically. Some carbs use an electric or hot water choke, but most Autolite carbs use hot air to open the choke plate. (the hotter the air, the wider the choke plate opens). Hot Air Chokes use heat produced from a heat riser tube (also called a hot air choke tube) which brings hot air up from the exhaust manifold or header. This hot air heats up a bi-metal spring inside the black choke cap, and as the spring heats up, it unwinds and gradually opens the choke plate to a fully opened position, allowing more air to enter the carb.

6) Do I need really a choke?
We have people from warm climates tell us that they don’t need a choke system, however this is simply not true, even if the outside temperature is 80 or 90 degrees in the morning. The cylinder walls, pistons and valves inside your engine are going to be the same temperature, or even a little colder, when the engine is cold. On the other hand, when the engine is at full operating temperature, it’s approximately 600 degrees. As such, the fuel requirements of a cold engine (90 degrees is cold compared to 600 degrees), are dramatically different than they will be when the engine is at full operating temperature. In the first ten seconds of operation, the engine needs twice as much fuel than when it is hot, and for that reason, a choke assembly should be used on all carburetors.

7) What is an Automatic Hot Air Choke?
Hot air is provided by a Heat Riser Tube (also called a Hot Air Choke Tube), which is connected to the exhaust manifold or header. In a stock application, this is a SEALED system, therefore there are no exhaust gases traveling through the choke tube. Instead, it draws cold air from the air filter into one end of the exhaust manifold. The heated air is then piped to the choke assembly by means of an insulated Heat Riser Tube, which warms the bi-metal spring in the choke cap, which in-turn unwinds and opens the choke plate. This process, at 40 degrees, takes 5-7 minutes, which happens to be about how long it takes your engine to reach it’s normal operating temperature. We like hot air chokes because the full opening of the choke plate corresponds with the time that it takes for an engine to reach it’s normal operating temperature.

What happens if you have an Autolite carb and you install a set of headers? That’s OK too, you can still use an automatic hot air choke. Instead of using the factory pre-bent stainless steel choke tubes that press into the exhaust manifold, we offer an extra long bendable insulated tube that clamps to the outside of the header pipe. These Hot Air Choke Tubes are available from Classic Inlines and can be ordered separately, or as an option when ordering a carb and/or headers. The open end of the tube, which is clamped to the header, pulls in fresh air which is heated and drawn up to the black choke cap in much the same way as the original tube. The only drawback is that the open end may draw in dirt, which could clog the choke assembly and prevent it from working properly. As such, we are working on a new choke tube which will be even longer, and will draw fresh air from the base of the air cleaner, there-by keeping out any dirt that could enter and clog the choke assembly.

NOTE: Hot air chokes were only used on Autolite carbs. All other carbs, including Weber, Holley, Carter, Edelbrock, Stromberg, and every other carb I can think of, used manual, electric, and/or hot water chokes.

8) How does a Manual Choke work?
If you spend enough time around older classic vehicles you will surely be familiar with the manual choke system. They consist of a knob and cable for the driver to be able to open and close the choke plate. These certainly have their place in trucks, farm equipment, lawn mowers and in some passenger cars. We do not like to see them used unless they were original to the vehicle. There are people that just prefer to be in CONTROL of the choke system and will install a manual choke for that reason alone. Manual choke conversions are really not a good option because of the unavailability of parts that are reliable enough to stay working. We very seldom do these types of conversions for that reason, except on high performance applications.

9) How does an Electric Choke work?
Electric choke assemblies differ from hot air chokes by the fact that the heat comes from the cap itself. Inside the black choke cap is a heating element, much like the heating element on your electric stove. It gets red hot and provides heat to the bi-metal spring to make the choke plate open. We do not prefer electric chokes because they go from closed to fully open in about 45 seconds. As stated earlier, it takes an engine 5-7 minutes to reach operating temperature, and in less than a minute the engine is not ready for such lean air/fuel mixtures that are going to be introduced into the engine. This causes driveability issues which include hesitations, flat spots, surging and dying. Anytime our clients will listen to us we try to discourage the use of electric chokes. The Ford electric choke caps that were first introduced in 1973 are unique. First, they operate on 7 volts, as opposed to the usual 12 volts. The 7 volts comes off a special terminal on a Ford alternator. In addition, they have ambient air temperature sensors built in and will not work below 60 degrees. Anyone who tries to use the original Ford electric caps alone will find they are pretty much useless. All of the Ford Motor Company vehicles 1973 and newer not only had the electric assist choke cap, but also had the hot air tubes running through the exhaust manifold. The idea was that the electric assist would open the choke cap at warm ambient temperatures when the engine didn’t’t need much help (fully open in about 45 seconds). It was used mainly as an emission device, not a totally electric choke.

10) What is the difference between the 65-67 and the ’68-69 Autolite 1100 carbs?
68-69 Autolite 1100-1V carburetors differ from the 65-67 carbs in 2 ways. First, they do not have a Spark Control Valve (looks like a power valve). For the engine to function properly with this carb, the distributor must have centrifugal advance (spring loaded weights inside) along with the vacuum advance unit. However the ’67 and older carbs (except ’66 and ’67 California Emissions) utilized the Load-O-matic distributor, which had vacuum advance only. The second difference is the CFM. In 1968 Ford put a 170 CID size carburetor on a 200 CID engine. If you ever looked at the engine specs, in 1968 the 200 CID engine is rated at 115 HP (this was generous, it is probably more like 105 HP). The 1967 and older engines were rated 120 HP. By changing the venturi inside the 1968 carb to the larger 1967 and older size, we can substantially increase your performance. The difference in the standing quarter mile is about 6 MPH. The cost for this upgrade is $30.

11) What is Annular Fuel Discharge?
Many enthusiast consider the Autolite 2100 (2V) and 4100 (4V) carbs to be
the best carb ever built. The engineering involved in their design was tremendous, and they were offered in several sizes so they could be used in unlimited applications. Unfortunately this feature was never incorporated into the Autolite 1100 (1V) series carb.

One company redesigned the 1100-1V carb, which incorporated annular discharge nozzles, however they were plagued with quality control issues (leaky carb bodies, faulty floats, etc). While these carbs were produced for a couple years, they are no longer in production, as far as I know (long story).

Annular Fuel Discharge carburetors produce greatly enhanced torque in the lower RPM range, more peak horsepower and torque, as well as better combustion and fuel burn through-out the entire RPM range. This results in superior fuel economy, improved throttle response, and it enhances overall performance. This is state of the art technology was patented by Ford Motor Company in 1957. As such, Autolite carburetors were the only carbs produced using this unique technique of metering, distributing, and mixing the fuel into the air stream for the next fifty years.

Down-leg boosters, found in most other carbs of this time period, utilize a single orifice to discharge fuel. Annular boosters, on the other hand, employ a series of several smaller orifices, which instantly change the fuel from it’s liquid state to a gas vapor. And as you probably already know, it’s vapor that burns, not liquid.
At lower engine speeds, slow air speeds in the venturi’s create a weak signal, which reduces the amount of fuel moving through the boosters. However annular discharge boosters offer multiple points for the fuel to enter the venturi, as opposed to a single discharge point. This yields measurable advantages, especially when large-volume carburetors are used in conjunction with a long duration camshafts. Annular-discharge boosters can greatly improve throttle response and driveability, even when a weak manifold-vacuum signal is present at idle, partial throttle, or under sudden acceleration.

12) What is the formula to calculate CFM?
Click here to calculate your CFM requirements.

13) Why am I having problems adjusting my new carburetor?
The number one problem in the industry concerning engine driveability is ignition timing. Most of the problems that you are experiencing are probably due to late timing, simply because the factory timing specs are just too retarded to get anything done. However, the engine really wakes up when you advance the timing properly. Most people use timing lights to set their timing, but timing lights may not be reliable. The reason for this is very simple. The timing marks are located on the harmonic balancer, which is mounted in rubber, and over the years they MOVE, when the rubber dries out. This is why we recommend replacing your harmonic balancer whenever you rebuild a motor (see our tech article on Harmonic Balancers).

Whenever customers call us concerning driveability problems (hesitation, flat spots, surges) 99% of the time, the problem is ignition timing. We will share with you an accumulation of many years of experience and if you follow our GOOF PROOF method -you will be rewarded with the best driveability and performance you have ever experienced.

All Ford engines run better, deliver more power, and give better fuel economy with the timing advanced BEYOND factory specifications. We should also note that premium unleaded fuel is highly recommended, especially in six cylinder engines. After you have adjusted your timing properly, the engine should not quite “ping” on full acceleration, or under load. If the motor PINGS, it’s an indication that the timing is advanced too far. Do not leave it like this…. PINGING, or pre-ignition, can and will severely damage the engine in a very short time (minutes).

For your engine to run properly the carburetor must be sized properly. There are several carbs that will work on the small six, including Autolite carbs, but not limited to them. Autolite offered eight different sizes in the 2100-2V series, as well as the 1100-1V, which was offered in three different cfm ratings.

14) What sizes are available in the 1100-1V and 2100-2V series carbs?
CFM Ratings are as follows:

Autolite 1V Carbs
Autolite 2V Carbs