1 or 2 carburetor

[airworks]

110 daily driver. Rebuilding heads now . I will be needing carburetor s. I have 2 carburetor to send back to Clarks and replace them with new rebuilt ones.Or I can buy 1 carburetor and use it I have the single carb plenum. It was on a car I purchased. Looks like cost will be close to the same. What single carb would I use if I go that way . Like the looks of single carb.

[66vairguy]

For a daily around town driver I would stay with the two stock carburetors. They are a bit more work to get sync'd, but once they are they are reliable if you use a good external fuel filter (carb inlet filters are not that great).

The single carb setup is simple, but without heating scheme for the inlet "runner" (like the old VW's) fuel tends to drop out at idle and low RPM resulting in poor throttle response and surging. There are ways to get around some of the single carb issues, but it's easier to just go with the stock two carb. setup - IMHO.

[airworks]

That what I was thinking. I was read about the 140 / 4 carburetor . Though maybe 2 would not be as bad . I will do the 2 with 2 single chrome air filters. I like the look also.

[bbodie52]

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.

http://www.corvairforum.com/forum/viewt ... 875#p90875


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
http://www.corvairforum.com/forum/viewt ... 225&t=6007

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

...I bought a Uni-Syn and only used it once. It seemed to me that at idle, there was barely enough air flow to raise the ball. It pissed me off and I put it away...

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.

UNI-SYN Carburetor Balancing Instrument Instructions.pdf

UNI-SYN Carburetor Balancing Instrument Instructions

(56.72 KiB) Downloaded 18 times

[airworks]

I have watched a lot of YouTube and read a lot . Wright now I have pulled the head off one side and removed valves. Will do one side at a time. THE leak down test failed on #6 exhaust valve. Added liquid to head and leak through. A friend ground the valve s and checked the seats. Now I will lap them.
Order the 2 head kit also stock rockers & valve seals from Clarks. I will order the carburetor in couple weeks after get the heads finish.
2. Valves had a T on face
#6 had a L that was the one that was leaking by . Is there a difference .
My first engine disassembly.