To have the 4 1 barrel carbs working great

[manofsteel]

Bought my 4 1 barrel carbs from Wolfs Enterprises down in Florida. They came perfect and he is very helpful with setting them up. I was told that after warmed up and at idle that there should be no suction from the secondary carbs on both sides. If there is I should unhook the linkage from primaries to the secondaries. On the left side this will be the linkage closest to the firewall. This will stop the suction. This should also smooth out the engine. Do all you engine and carbs gurus agree with this formula? I did this but not all of the way and with my linkage connected, I do have suction and engine NOT running smooth. I can’t wait for the feedback from all of youa’l
Jim H
1965 Monza Convertible 140
Slower Lower Delaware

[Dennis66]

Is the suction from the top of the carb, or from one of the vacuum ports? Dennis

[bbodie52]

The two primary carburetors in a 4x1 four carburetor system have choke systems, external vacuum ports, and idle speed and mixture screws...





The secondary carburetors are stripped-down models that lack any idle mixture or idle speed screws, or any choke mechanism or external vacuum ports.




All four carburetors have a throttle butterfly valve on the bottom. But only on the PRIMARY carburetors the throttle butterfly valve is held partially open by either the choke fast-idle mechanism or, when the engine has warmed-up, by the idle speed screw. This partial open setting allows the engine to idle, by letting a small amount of engine intake manifold vacuum to draw in air — to pass through the carburetor intake to mix with gasoline and keep the engine running with no throttle application from the driver. Under this condition, if you were to place your hand momentarily over the top of either PRIMARY carburetor, you would feel some suction on your hand as air is passing through because of the partially opened throttle butterfly valve on the carburetor bottom.

On the other hand, the two SECONDARY carburetors should have their throttle butterfly valves fully closed at idle. No air is admitted into the intake manifolds from the SECONDARY carburetors at idle. The throttle butterfly valves on the two SECONDARY carburetors are controlled by the main linkage, and it is PROGRESSIVE in nature. The SECONDARY carburetors are opened by the linkage only at higher engine speeds and under heavy application of the throttle by the driver. AT IDLE, BOTH SECONDARY CARBURETOR BUTTERFLY VALVES ARE FULLY CLOSED. WHEN PLACING YOUR HAND OVER THE INTAKE OF EITHER SECONDARY CARBURETOR AT IDLE YOU SHOULD FEEL NO SUCTION. BECAUSE THE SECONDARIES SHOULD BE FULLY CLOSED.

Since a secondary carburetor has no idle fuel circuit, it has no ability to mix any gasoline with the air if the throttle butterfly is slightly opened. Sometimes the throttle linkage is stuck partially opened by dirt, deposits around the throttle shaft, or an improperly acting throttle linkage mechanism. IF THE THROTTLE BUTTERFLY ON EITHER SECONDARY CARBURETOR IS NOT CLOSING COMPLETELY AND IS ADMITTING A SMALL AMOUNT OF AIR, A ROUGH IDLE WILL LIKELY OCCUR. This condition is essentially a vacuum leak through the secondary carburetor, due to a sticking throttle. The cause of such a vacuum leak must be determined, to allow the secondary throttles to fully close at engine idle, when the secondary carburetor is not supposed to be active.

The last few pages of the attached 1965 Corvair Assembly Manual - CARBURETOR & FUEL SYSTEM provide an illustration and discussion of the secondary carburetor linkage and adjustment. The attached DELCO ROCHESTER - Models H, HV Carburetor Service Guide also provided a technical description of the secondaries and their linkage adjustment.

[66vairguy]

Brad gave a good description.

Note: A "notch" in the primary carburetor throttle plate was added that aligned with the idle mixture port. This was done to promote better off idle response as the throttle was opened. I don't have my notes handy, but I think the change was made on the 1962 models. You can only install the throttle plate one way so the notch lines up.

The secondary carburetors have a solid throttle plate (no notch). The lack of a notch means that the throttle plate, with a beveled edge, can be installed upside down in the throttle shaft slot. If the beveled edge is facing the wrong way a poor seal will occur when the throttle plate is closed. The bevel angle is minor and easy to miss when assembling a carburetor.

The other issue is the throttle plate may be off center in the throttle shaft slot. I always snug up the screws, check with a bright light for gaps, and if all is good I tighten the throttle plate screws AND double check. The screw end opposite the head should be "peened" so it won't come loose (and end up in a cylinder and cause head damage). I've seen a couple pictures of carburetor throttle screws embedded in the top of the cylinder head chamber.

[manofsteel]

Guys that was a super response and what you all said confirmed of one reason why me carbs is allowing the engine to run smooth at idle. Getting these 4 carbs to all work together is a tough job especially since I never had 4 carbs on my Monza back in 1969 and that was a Monza 110 1965 also. Lot more simple then. If after all of this will my Monza 140 now run on only 2 primaries and blocking off the secondaries? Might be a lot more simple to having a smooth running engine. Thanks for replies
Jim H
Delawar

[Dennis66]

I kind of wondered about the secondary carbs maybe not having any vacuum ports or idle circuits. 1974 was a LONG time ago, and my 4 carb engine was a conversion, not big valve heads, but stock heads with extra flanges that bolted on. I do seem to remember my secondaries having no choke plates, but I also think they may have been 1960 carbs. I removed them and blocked off the mountings with aluminum plate. Dennis

[66vairguy]

I kind of wondered about the secondary carbs maybe not having any vacuum ports or idle circuits. 1974 was a LONG time ago, and my 4 carb engine was a conversion, not big valve heads, but stock heads with extra flanges that bolted on. I do seem to remember my secondaries having no choke plates, but I also think they may have been 1960 carbs. I removed them and blocked off the mountings with aluminum plate. Dennis

Over the years I've seen a few four carburetor engines that used primary carburetors (without chokes) for secondaries. After all these decades anything is possible. As others have said, Bob Helts Rochester book is a valuable tool to figure out what the carburetors are. The 1960 carburetors can work well as secondaries because they have the solid throttle plate AND an idle mixture circuit that was incorporated on the 68-69 secondaries per Bob Helts's book. It solves the occasional mis-fire at idle on 140HP engines. Since the simple 62-63 carburetor is easier to find, I use them for secondary bases and install the solid secondary throttle plate.

I've mentioned it before, but I always install Clark's throttle shaft return spring on secondaries. See https://ssl.corvair.com/user-cgi/search ... arch=c1916

I always tell new folks that the two carburetor 110HP engine is a real gem, then the club guys say "Why do all your engines have four carburetors?" I reply I like the look and the extra go. My Corvairs are hobby cars, so I put up with the extra maintenance. If you drive your Corvair a lot, and don't like to tinker, the 110HP is a better choice.

[acarlson]

To precisely adjust your carbs get a uni-syn gauge - Clarks C1443:

https://ssl.corvair.com/user-cgi/catalo ... nd_page=58

[bbodie52]

To precisely adjust your [PRIMARY] carbs get a uni-syn gauge - Clarks C1443:

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 tune-up 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.

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.

viewtopic.php?f=55&t=13170&p=90875#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
viewtopic.php?f=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

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.

[acarlson]

The uni-syn can also tell you if you have a linkage problem that is not allowing the secondary butterfly to close completely.