- Corvair of the Month
- Posts: 9675
- Joined: Mon Aug 06, 2012 12:33 pm
- Location: Lake Chatuge Hayesville, NC
I would like to encourage you to expand on your earlier post and tell us more about yourself, as well as about your Corvair. If you can provide your personal assessment of your mechanical skills and abilities, that would help a lot. Members of the Corvair Forum love to be helpful in assisting other Corvair owners with technical support and advice, but it helps a lot if we have some understanding of your technical background and mechanical abilities, your Corvair-related knowledge, etc. Helping us to know more about you will help us to write comments to you that are tailored to your needs and experience. Knowing your specific location is also useful, because knowing where you live can sometimes suggest possibilities.
Effective troubleshooting, fault isolation, and repair by "remote control" over the Internet is difficult at best. It would be easy to jump to a conclusion based on your brief description and point you in the direction of a vacuum leak, faulty carburetor, bad ignition system, etc. But at this point we simply know too little about you, your car's history and symptoms, and your ability to test and repair the car yourself. If you have automotive repair experience, tools, a place to work, etc., we can help guide you with Corvair-specific information. Your approach may be quite different if you have little or no experience as a "shade tree mechanic". Professional mechanics with Corvair experience are somewhat rare. Corvair owner's clubs (CORSA — Corvair Society of America) are scattered around the nation. Correcting your problem, if you lack tools and experience, may require some assistance from a local club (if there is one near you), or a Corvair mechanic.
The link below will provide you with a list of useful websites that are Corvair-related. Some of the links will lead you to an extensive technical library that will allow you to download shop manuals and other technical references in Adobe Reader format at no cost. There is also a link that will help you to locate nearby CORSA (Corvair Society of America) club chapters. While the Corvair Forum can be very helpful as you work on your Corvair, having local friends and contacts in your region who are knowledgeable about the Corvair can also be very helpful. These family-friendly CORSA chapters often offer picnics, group scenic drives, technical training and assistance, car shows, and competition events that can greatly enhance your enjoyment of Corvair ownership. You will also find a list of essential Corvair parts suppliers. Clark's Corvair Parts in Shelburne Falls, MA is the biggest and oldest Corvair supplier in the world. You will find a link that can provide you with a series of videos that amount to a tour of the Clark's Corvair Parts facilities. I think you will be amazed at the quality of the reproduction components they offer — particularly the interior carpeting and re-upholstery items. Parts suppliers such as this truly make our Corvair hobby possible.
Common and Useful Corvair Websites
bbodie52 wrote:There is no simple, or compressed method to tune and troubleshoot a Corvair engine. A certain amount of knowledge or understanding is essential for the person doing the tuneup to interpret the results and then to be able to make logical adjustments accordingly. I would encourage you to do your homework, ask questions for clarification when needed. and follow the guidance below and in the shop manual to ultimately get the desired results with your Corvair.
If a carburetor overhaul appears to be appropriate, some of the info below may be of help...bbodie52 wrote:Here is a fair amount of tune-up info, but if you can work your way through it the explanations may help with your understanding of how the various subsystems interact with each other, and why the proper sequence should be followed so you don't end up adjusting one area improperly to compensate for another area that isn't functioning properly.
The dwell tachometer and timing light are the most common items thought of when working with an older engine in a classic car. As previously mentioned, however, there are ways to work around the lack of these tools. Adjusting the ignition points gap with a flat feeler gauge is a substitute for having a dwell tachometer. Setting the dwell with an electronic instrument is more accurate, however. The tachometer portion is needed to measure idle speeds and possibly to perform other tests where engine speed measurement is needed. It is possible to static-time your ignition system with a strip of paper placed between the ignition points. The engine timing mark can be manually positioned to the desired setting on the crankshaft pulley, and the distributor can be slowly rotated until the points just start to open and release the strip of paper. The distributor is then tightened and the mechanic has established an initial static timing setting. Of course, having a timing light makes things much easier, improves accuracy, and permits visual confirmation that the centrifugal advance is functioning. A vacuum gauge can be used for carburetor synchronization and other carburetor tests, and most vacuum gauges also double as a pressure gauge for measuring fuel pump output pressure. A UniSyn gauge, as shown below, measures airflow through each carburetor throat, and is an accurate way for synchronizing multiple carburetors at idle speeds and at partial throttle. A multimeter is a useful tool for troubleshooting and diagnosing electrical and charging system problems.
Many ignition systems in Corvairs have been upgraded by fitting an electronic ignition system to the distributor. These electronic ignition systems eliminate ignition points and condenser, which makes engine tuning somewhat easier and eliminates the need to periodically replace worn ignition points. The breakerless ignition system utilizes an optical or magnetic trigger to control the ignition coil. The system eliminates the need for a dwell meter or flat feeler gauge for ignition points adjustments. (A wire-type feeler gauge is needed for adjusting spark plug gaps). The tachometer portion of a dwell-tachometer, however, is still useful.
Learning to work with the two Rochester primary carburetors on the Corvair really isn't all that difficult. But you should take the time to review the shop manuals and other attached manuals to get a better feel for what you are trying to accomplish. It is important to perform tuning steps in the right sequence, as outlined in the shop manuals and in the video below. Many of the tuning steps can impact the results found in other steps. There is a logical progression in tuning a Corvair engine, and skipping around or tuning components in a random order can only serve to confuse the outcome. The Delco Rochester service manual that I have attached is a good supplement to the Corvair shop manual. About half of the manual is dedicated to explaining the various subsystems and components of the Rochester HV carburetor. To some extent these carburetors perform as you would expect a computer-controlled fuel injection system and ignition system to operate — but they were designed at a time when computer-controlled systems that were designed to respond to sensor input throughout the car would only have been a dream. The various carburetor and ignition subsystems respond to engine temperature, engine speed, airflow and vacuum changes, etc. much like a modern engine — but without all of the sophisticated electronics and sensors. Engineers were attempting to accomplish the things we do now, but with much less sophistication — but still making changes as engine speed, throttle position, engine vacuum, and fluid and air flow characteristics varied. If you take the time to read through the Delco Rochester manual, you might come to understand how the choke system functions, what an accelerator pump does and why it exists, and how the distributor is designed to adjust timing at low engine speeds and at higher engine speeds using both a vacuum advance and a centrifugal advance to provide the correct timing at various engine speeds and load settings. A good understanding of how these systems work and what they are supposed to do can be a great help when tuning and troubleshooting your engine.
The links, videos, and attachments below should help you to understand how to work with a dual carburetor engine. Try not to be intimidated by two physically separated carburetors. They really function very much like a single two-barrel carburetor, but are physically separated from each other out of necessity due to the layout of the flat air cooled engine with cylinders opposed to each other. The Corvair engine layout is in many ways similar to many motorcycle engine configurations. It usually takes an experienced automobile mechanic a little adjustment time to get used to the way things are done on a motorcycle. The aluminum, air cooled flat six Corvair engine often is seen as a challenge to an automobile mechanic, who is not used to the "strange configuration" found in a Corvair.
The entire shop manual and many other Corvair technical references can be downloaded at no cost using the following link...
Common and Useful Corvair Websites
Watching the video presentations below helps to provide insight and understanding about proper sequencing of the tuneup steps and procedures. Skipping around can insert obstacles and problems with getting the engine properly tuned.
The portion of the first video segment toward the end (Part 1, 5:10) and at the beginning of the second segment discusses throttle linkage adjustments and carburetor synchronization.
Tuning the Corvair Engine — Part 1
Tuning The Corvair Engine — Part 2
bbodie52 wrote: The Uni-Syn Carburetor Balancing Instrument is a tool that I remember as far back as the 1950s and 1960s. It was designed for use in multi-carburetor automobiles, motorcycles, etc. that were initially common in European vehicles, but were later found in American vehicles like the Corvair.
The Uni-Syn is an airflow gauge that must be calibrated to match the specific engine airflow moving through the carburetor throat. The flow control in the center of the Uni-Syn is mounted on a threaded pin. Rotating the flow control raises or lowers it, which increases/decreases the air gap, which impacts the air velocity passing the oriface that allows some airflow to pass through the gauge. With the Uni-Syn held firmly on the carburetor intake with the engine idling, the flow control is adjusted so that the plastic float is approximately centered in the glass sight tube. Once calibrated, the Uni-Syn can be moved back and forth between the two primary carburetors to compare airflow at idle. The goal is to play with the idle speed screws to get an even airflow level that matches between both carburetors, and at the same time produces the desired idle speed. Before fine-tuning this idle balance with a Uni-Syn, the ignition system, idle speed and idle mixture should have been adjusted following the standard procedures as described in the factory shop manual. The balancing step with the Uni-Syn gauge is added at the end of the tuning procedure to measure actual airflow though both carburetors at idle, and balancing that airflow using the airflow meter as a measuring tool, rather than simply relying on a physical balanced "calibration" using a strip of paper to detect initial contact between the idle speed adjustment screws and the carburetor linkage, followed by counting the screw turns needed to obtain the desired idle speed (and ensuring that the same number of screw turns are applied to each screw). That procedure achieves a fairly close initial setup. The use of the Uni-Syn airflow gauge as a final step ensures balance between the two carburetors by measuring actual airflow.
Once the balanced idle airflow and desired idle speed have been achieved, a similar procedure can be used to synchronize the airflow when the carburetors are held open at a faster engine speed by the throttle linkage. Again, the shop manual procedure can be used to set the initial mechanical balance between the two sides of the throttle linkage. The linkage segment connecting the accelerator pedal to the cross-linkage between the two carburetors is temporarily disconnected, and a turnbuckle is temporarily attached to hold the throttle opened against the pull of the throttle return spring.
The turnbuckle can be adjusted to hold the throttle open at approximately 1500 RPM. The Uni-Syn center flow control is readjusted to re-calibrate the float to a position somewhere in the center travel of the sight tube, based on the increased airflow through the carburetors at the higher steady RPM maintained by the turnbuckle arrangement. As with the idle synchronization procedure, the re-calibrated Uni-Syn is used to measure the airflow moving through the two carburetors. The goal is to fine-tune the threaded portion of the carburetor actuation linkage so that the same airflow reading is attained on each carburetor, but this time with the throttles held open by a pull on the throttle linkage, instead of by the setting of the idle speed screws. When the airflow has been balanced using the throttle linkage adjustment, the balancing procedure has been completed and the normal accelerator pedal throttle linkage can be reconnected.
TIPS & CLARIFICATION...
With the engine at idle, you want to open the Uni-Syn flow control as much as possible, but still keep the float in the sight glass at about mid-level. Then check the other carburetor, which you want to read the same flow rate. You may have to adjust the flow control a few times as you adjust the carburetor settings. Just remember to check each carburetor with the flow control set at the same point, and to keep the sight glass in the vertical to prevent the float from hanging up in the tube.
The wheel in the Uni-Syn venturi controls the flow through the tube, or in other words how high the bead is in the cylinder for a given engine speed. You need enough flow to not strangle the engine, and the bead works just as well in the lower third (which still lets good air flow through). Make sure the idle speed doesn't drop when you place the tool on the carb: if it does, open it up.
Before setting the carbs, make sure that the ignition is right: points and timing set, good wires and plugs. Rich running is often blamed on carbs when in fact it's a weak, retarded spark. Check the throttle shafts: loose ones let in air and lean the mixture, raising idle speed, as well as throw off the linkage action. Check the linkage that connects the carburetors. if it's loose, one will open before the other. Make sure there are no vacuum leaks.
With a twin carburetor set up, disconnect the linkage that connects one carburetor to the other. Set the idle speed with the linkage screws first. Use the Uni-Syn to check that each carburetor is drawing equally at idle. This may take a few tries until you get both drawing equally at the speed you want. Blip the throttle to see if they come back to those settings (worn throttle shafts can fool you). Set the idle mixture screws in accordance with the shop manual instructions. Check the balance again. Hook the linkage back up. If one carburetor now draws more, adjust the linkage until it's back to roughly equal.
Once the carburetors are drawing equally at idle, hold an engine speed: at about 1500 RPM. This checks that the mechanical linkage is pulling equally. You'll need to open up the Uni-Syn center wheel to draw more air and bring the bead down in the tube. If both carburetors are within a bead's thickness of each other, that's good. If one is definitely off from the other, the higher flow carburetor's linkage is being pulled more than the other. You'll need to figure out why that's happening mechanically to rectify it.
One of the key factors when troubleshooting, tuning, and working with Corvair carburetors is careful synchronization of both carburetors. If it has been some time since your carburetors have been overhauled, I would suggest that cleaning and rebuilding both carburetors would be appropriate, since this is the first step in ensuring that your fuel system is properly balanced and in good operating condition. The Rochester carburetors on the Corvair are relatively simple. I rebuilt my first carburetors at age 16 without difficulty. But I would suggest reading through the material below and browsing through the attached documents and manuals prior to tackling this project. If you have any questions you should ask them here on the Corvair forum prior to starting your carburetor cleaning, rebuilding, and engine tuneup. The training videos below should also help you with better understanding of the concepts behind properly maintaining and tuning your engine.
The carburetors must be completely disassembled to allow you to soak the metal components in carburetor parts dip. Rubber components and plastic items, and gasket material would not survive the chemical cleaner solution. All of these items are included in standard carburetor rebuild kits. The components you would need can be found in the Clark's Corvair Parts online catalog. I would suggest browsing through pages 55-59 of the catalog to familiarize yourself with the items that are available. I know that I've given you a lot of material to look at, and it is not my intent to overwhelm you with details. But if you take the time to review the manuals that are attached, watch the tuneup videos that were written by GM to train their mechanics, and then ask your questions here on the Corvair Forum, you should find yourself to be well prepared for the actual project.
http://www.corvair.com/user-cgi/catalog ... ow_page=55
I hope that the material I write below will serve to clarify some things and not just overload you with technical information...
I wanted to start by making sure that some important insulators were not accidentally omitted when your car was worked on in the past…
Carburetor rebuild kits often contain a thin gasket to seal the underside of the carburetor where it mounts on the intake manifold. The Corvair carburetors need a plastic insulator to isolate the base of the carburetor from the intake manifold, which prevents the gasoline inside the carburetor from boiling or vaporizing if excessive heat is allowed to transfer from the hot aluminum intake manifold on the cylinder head to the carburetor body. These plastic insulators can be easily damaged when removed. Clark's Corvair Parts bundles gaskets and insulators together. They are listed near the top of page 56 in the catalog http://www.corvair.com/user-cgi/catalog ... ow_page=56.
After reading through the above material please let me know if you need any further clarification. The attached DELCO ROCHESTER - Models H, HV Carburetor Service Manual may help you somewhat with the carburetor identification. It will also help you to understand each of the carburetor subsystems and many of the factory changes, so that you can better understand what the changes were and what they were intended to accomplish.
- 1961 Chevrolet Corvair Shop Manual - Section 6a - Engine.pdf
- 1961 Chevrolet Corvair Shop Manual - Section 6a - Engine
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- 1961 Chevrolet Corvair Shop Manual - Section 7 - Engine Tune-Up.pdf
- 1961 Chevrolet Corvair Shop Manual - Section 7 - Engine Tune-Up
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- 1961 Chevrolet Corvair Shop Manual - Section 9 - Fuel & Exhaust Systems.pdf
- 1961 Chevrolet Corvair Shop Manual - Section 9 - Fuel & Exhaust Systems
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- 1962-1963 Supplement - Chevrolet Corvair Shop Manual - Section 6a - Engine.pdf
- 1962-1963 Supplement - Chevrolet Corvair Shop Manual - Section 6a - Engine
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- 1962-1963 Supplement - Chevrolet Corvair Shop Manual - Section 7 - Engine Tune-Up.pdf
- 1962-1963 Supplement - Chevrolet Corvair Shop Manual - Section 7 - Engine Tune-Up
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- 1962-1963 Supplement - Chevrolet Corvair Shop Manual - Section 9 - Fuel & Exhaust Systems.pdf
- 1962-1963 Supplement - Chevrolet Corvair Shop Manual - Section 9 - Fuel & Exhaust Systems
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- 1962-1963 Supplement - Chevrolet Corvair Shop Manual - Section 12 - Specifications.pdf
- 1962-1963 Supplement - Chevrolet Corvair Shop Manual - Section 12 - Specifications
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- DELCO ROCHESTER - Models H, HV Carburetor Service Manual.pdf
- DELCO ROCHESTER - Models H, HV Carburetor Service Manual
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Lake Chatuge, North Carolina
1966 Corvair Corsa Convertible
Check to see that the main jets are clear, sounds like it's running lean on progression. As for the difficult hot restarts, my car had the same issue. Turned out fuel wasn't being pumped to the carb- electric under tank pump and mechanical pump delete will solve that once and for all.
- Corvair of the Month
- Posts: 9675
- Joined: Mon Aug 06, 2012 12:33 pm
- Location: Lake Chatuge Hayesville, NC
Here is a post from Facebook today that shows what kind of help is sometimes offered in a solid CORSA club chapter...
the combined action of a group of people, especially when effective and efficient.
DETROIT AREA CORVAIR CLUB (DACC)
https://www.facebook.com/groups/1754042 ... highlights
John Allesee wrote: (7/2/2018)
I would like to thank the Garage Squad for making an appearance at my house on Saturday morning. Pete Koehler, Ian Charles Smith, and Gary Komora showed up about 9:45 am and promptly started to get my engine removed. I had already disconnected most of the stuff and had the wagon on jack stands, so things went fairly quick. The engine was pulled, mounted on a stand, and we removed the left head. We found the problem with my non-existent compression in #6 - both compression rings were broken. We replaced the rings and with a little backyard mechanic ingenuity, we got the cylinder back in place. Torqued down the head and re-mounted the engine, leaving me to do a valve lash and reconnect all the wiring, fuel lines, vacuum lines, and generator. All of this was done in under 3.5 hours. At 1:15 we were all washed up and enjoying burgers and drinks. Thanks again guys, your help is greatly appreciated.
Lake Chatuge, North Carolina
1966 Corvair Corsa Convertible