From Veeduber@aol.com Thu Aug 22 16:59:50 1996 msgnum: msg16988 Date: Thu, 22 Aug 1996 17:58:34 -0400 From: Veeduber_at_aol_dot_com Subject: Re: automatic chokes >From: tim_at_sicom_dot_com (tim) To: Veeduber_at_aol_dot_com What is your opinion of the automatic choke. I hear all kinds of contradictory information. I have a 1970 bus equiped with a stock 1600 single port with a 30 pict 3 carb. "St. Muir" says to disconnect it altogether. If I keep it functional, how do I adjust it properly? Tim, The electrically powered automatic choke on Solex carbs is a good idea. Properly adjusted, they provide quick starts during cold weather and enhance warm-up without any negative effect during cruise. The choke consists of a heater coil that heats a bi-metallic spring. When the spring is cold it holds the choke-plate across the inlet of the carb. The spring tension is low enough to allow the choke-plate to be opened by the increased air-flow when the throttle is opened. When the bi-metallic spring is heated by the electric heating element it moves the choke-plate to the vertical position and holds it there against a stop located on the outer body of the carb. With the bi-metallic spring properly installed so as to engage the lever on the end of the choke-plate shaft, adjustment is nothing more than rotating the bi-metallic spring holder so as to bring the choke-plate to a nearly horizontal position. It will only move one way and the 'nearly' is defined by fine-tuning; if it does not start and idle reliably, rotate it a little more -- or a little less(!) until the engine starts reliably and will idle without any throttle. If you live where it snows you'll probably want to adjust the choke each spring and fall, providing more choking action for winter starts, less for summer. There are a couple of marks on the body of the choke to facilitate this. The range of adjustment is very small so don't get carried away. The choke is in good condition if the shaft is free to rotate, the heating element unbroken (does it get hot?) and the travel-limiting pin undamaged (the pin rides in an arc on the throttle-positioner quadrant-plate (the thing with the teeth against which the upper part of the throttle lever rests; look for the adjusting screw; it fits against the quadrant-plate) on the driver's side of the carb). If the heater element is damaged, replace it. The element, a coil of nichrome wire, is riveted into the housing. Replacement consists of replacing the housing. And yes, the element comes with different heat ranges, some that warm up faster than others for use in warmer climates. If the shaft does not rotate smoothly soak that portion of the carb in carb cleaner for 24 hours after first removing the plastic insulator behind the choke heater element. Since the choke sees virtually no motion, as compared to the throttle, it is unlikely that the choke shaft or bores will wear out. Failure to move freely is usually due to an accumulation of crud. Proper cleaning and a shot of low-residue silicon lubricant is usually all that's needed to restore smooth operation. But sometimes corrosion is a factor. If the body of the carburetor or the choke shaft is corroded, it must be completely dismantled and polished smooth. This calls for removal of the butterfly valve, the fasteners of which must be carefully straked on re-assembly. Failure to strake thee fasteners (ie, to peed them over) can cause them to be sucked into the engine. Feeding screws down the carb is never a good thing to do. The choke is electrical and starts working as soon as you turn on the key, meaning it's function is NOT directly related to the operation of the engine. Normally, it takes three to seven minutes for the electrical heater element to shut off the choke but expect it to take longer -- as it should -- during really cold weather, shorter during hot weather. The elegance of this system is that the function of the choke is 'conditioned' by the ambient air temperature. Cold day, longer choking action, warm day, less. Note that if you leave the key on WITHOUT starting your engine, the choke will still actuate -- and may be fully opened (unchoked) when you finally get around to starting the engine. If you fail to understand this point, and have a habit of turning on the key some time before starting the engine, you can easily come to the conclusion that automatic chokes 'don't work', as a lot of people have done. In the same vein, a seemingly non-related electrical problem can prevent the choke from actuating properly, leading to poor fuel economy and other ills. The electric choke is an intelligent, well-engineered replacement for the troublesome and failure-prone mechanical choke fitted to the early 28PIC carb. It offers a big step forward in engine management. Failure to understand -- or appreciate -- how the electrically operated choke operates has caused people to follow the advice of St. Muir, who obviously did not understand the thing, and tear it out. Don't do it. Instead, learn how it works and how to maintain it. You'll be rewarded with a vehicle that starts more reliably and warms up faster, plus an engine that will last longer. Since this question comes up quite frequently I am going to make this a general post. -Bob On a cold morning, simply depress the throttle -- once. This gives a shot of gas from the accelerator pump and causes the throttle positioner quadrant-plate to snap into position by the action of the bi-metallic spring in the choke. Now turn the key. The engine should start within three revolutions and should idle with your foot off the accelerator. If it doesn't, find out why and fix it. On cold mornings, let the engine warm-up at least five minutes before driving off. This has to do with proper oil circulation and will add years to the life of your engine. On REALLY cold mornings wait until you feel some heat coming from the vents.