http://classicinlines.com/autolitecarbs.asp#55) How does the choke system work?
When the gas pedal is pressed all the way to the floor, when the engine is cold (at whatever ambient air temperature), the choke plate closes and air flow is reduced. Once that is done, a couple of pumps of the gas pedal will provide the initial charge of fuel for the engine to start. Once the engine starts, a choke unloader will open the choke plate about 1/8Ē. From there, as the engine heats up, the fuel requirements continue to lessen (it can run on a leaner mixture). Heat produced from a heat riser tube (from the exhaust manifold or header), or an electric choke, provides heat to a bi-metal spring inside the black choke cap. As the spring heats up it unwinds and gradually opens the choke plate to a vertical position, allowing more air to enter the carb. 6) Do I need really a choke?
We have people from warm climates tell us all the time that they donít need choke systems, however this is simply not true. Even though it may be 80 or 90 degrees outside 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 at full operating temperature it is approximately 600 degrees. 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 operating temperature. In the first ten seconds of operation the engine needs twice as much fuel than when it is hot. For that reason, we like to use choke assemblies on all carburetors. When properly adjusted, an automatic (hot air) choke (especially an Autolite 2100 or 4100) will allow a carbureted vehicle run almost as well as fuel injection.7) What is an Automatic Hot Air Choke?
Hot air is provided by the heat riser tube connected to a sealed passage in the exhaust manifold. This is a SEALED passage, therefore there are no exhaust gases traveling through the choke tube. It allows cold air from the air filter to enter one end of the exhaust manifold, which is warmed up and then pass through the insulated tube to choke cap on the carburetor. The heated air warms the bi-metal spring, 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.
Hot air chokes were only incorporated in Autolite carbs, and won't work if you swap your Autolite carb in favor of a Weber or Holley. Weber and Holley carbs come with various other types of chokes including manuel, electric, or even hot water. But 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 brings, 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. 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'tít need much help (fully open in about 45 seconds). It was used mainly as an emission device, not a totally electric choke.