Corvair Carb Reference page for 2020.

Builders, Here is our Carburetor Reference page for 2020. It is a collected index of stories and videos about Carb Options for Corvairs.

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It is my personal recommendation that new builders plan around using one of two carbs, either a brand new Rotec TBI or a new Marvel Shebler. MA3-SPA. You can read though the stories presented here to gain more insight, and understand what has historically been used, and how we get to the current recommendation. Here are the most current Stories:

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New video on Rotec carbs for Corvairs.

Information on why this is the new ‘standard’ recommended carb

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Stromberg carb procedures in 2020, With video link.

Outlines why these are no longer a primary recommendation .

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New MA3-SPA – Available from SPA/Panther

The source for new MA3-SPA carbs

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Here is a sampling of recent testing:

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Shootout at the Stromberg corral (2019)

This is how we identified issues

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Stromberg Shootout, Pt #2 (2019)

This was looking for solutions and retesting.

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MA3-SPA Test Runs. (2019)

Testing to verify the quality of overhauls.

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Safety Alert: Excessively Rich MA3-SPA Jetting. (2017)

Alert  about some rebuilt MA3-SPA carbs which were jetted richer than stock.

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Critical Understanding #10 – Carb Ice (2017)

An article which became part of the MOP manual

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Inexpensive carb testing (2017)

We still look for solutions which would keep flying affordable.

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Critical Understanding #4, ANY loss of RPM is Detonation. (2016)

Understanding that lean operation leads to detonation.

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The notes below cover the broad variety of Carbs that have flown on the Corvair, and some thoughts on why I choose simplicity when it is available, and the development of our intake manifolds.

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Above, an overhauled NAS-3. While a proven workhorse, I no longer encourage new builders to plan on this carb. 

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An intermission to remind that very little good comes from discussion groups:

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Internet speculation vs First hand experience….. . 

A drama filled example of people “Chiming in” on discussion groups, and how inane some of the comments are.

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Speculation vs Experience Pt #2, Actual issue identified.

How I understood the issue by having personally tested the builders engine at a west coast college…..It was a propeller adjustment.

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Below is a list of stories have written on Corvair carburetors. You can click on any color title to read the whole story:

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Air / Fuel ratios on Corvair carbs.  (2016)

A look at the range of air fuel mixtures we use, and how we test this.

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So you like the idea of auto gas…. (2018)

Corvair run on auto fuel, but you have to know stuff like this.

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New Ellison Carb supplier, NV Aero.com (2016)

Steve Glover bought the rights to and all the tooling for Ellison carbs.

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Ma3-SPA carb orientation, (2016)

A dumb story about how internet discussion groups miss the point.

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Carb Orientation Pt. 2: Internet Reading Comprehension Failures.  (2016)

A second example of why discussion groups are better for drama than tech info.

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Running your engine “Over-square”? (2015)

Info on why not to lug your engine and why 2700rpm is min. static rpm.

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How I became a genius in 6 minutes (2014)

Why you don’t use a British car carb on a plane

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Fuel Injection – Corvair flight engines reference page  (2013)

Because in any Carb discussion, someone will incorrectly assume I have never tried FI on a Corvair.

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Stromberg Carbs  (2013)

The world’s most prolific light plane carb, but this is an older story, read the update at the top.

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MA3-spa carb pictures, Wagabond notes.

The MA3 is the most popular carburetor on Corvairs today. Please read the more current story above.

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Carb applications, choices people make

A story of why builders professional background tend to choose carbs.

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Intakes and Internet myths

Notes on why the intake works so well.

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In Search Of … The Economical Carburetor

A story of testing a $160 carburetor.

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A question of Carb location…..

A warning about top mount carbs.

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Deal of the Day,simple MA3 carb. (Sold at 1 am, 9/1/13)

Good photos of a straight MA3.

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Below are the Group numbers of our intakes and the numbers we assigned to the popular Corvair carbs. You can see how this is part of our Group numbering system by studying the complete numbering system on the “Prices” section of our main page, FlyCorvair.com. These are all discussed in my Conversion Manual

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Intakes and carburetors  group (3600)

3601(S)- Standard Intake manifolds

3602(A)- Marvel MA3-SPA

3602(B)- Stromberg NAS-3

3602(C)- Ellison EFS-3A

3602(D)- Sonex AeroCarb  –  38mm

3602(E)- Zenith 268

3602(F)- Rotec TBI 34mm

3602(G)- 1 barrel Carter downdraft

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Commentary on Carbs:

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When it comes to carbs, I have always liked Strombergs and MA3s because they have literally millions of hours feeding air and fuel into flight engines. I know them and trust them, but in recent years we have had trouble with rebuilt ones having consistent quality for builders to use them directly out of the box. In years past it was not this way, but today it is. These carbs were always my first choice to put on a plane because they are aircraft carbs, they are not just playing the role. They are doing the job they were designed to. Today, my recommendation is that builders focus either on a new Rotec, or a new MA3.  These are not the cheapest path, but without question, they are the most reliable.

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My father,William E. Wynne Sr. 1925-2017 was a lifelong military engineer who spent a lot of time working in places where the people who don’t like your project are literally going to try to kill you. He upheld that the piece of machinery that has the greatest reliability requirement is the combat firearm. In these tools, reliability is an absolute requirement. All other considerations about them – weight, accuracy, firepower, cost, etc. – all are meaningless if you ever need to use one and squeezing the trigger produces a soft noise rather than a loud one.

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Notice that the requirements of aircraft carbs are very much like combat firearms. When you push the throttle in, you really want to hear a loud noise, not a soft one. If your glide path leads to a place 200 feet short of the runway threshold, and pushing the throttle in gives the undesired soft noise, you will not be comforted by thoughts of how cheap, how light, how available, easy to tune or install it was, or any other factor that made it attractive in the hangar. Reliability alone gets you back to the airport.

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Consider this: The MA3 was designed about the same time that the Soviet Red Army adopted a device called the AK-47. Sixty plus years later, both of these devices have been used in countless numbers all over the  globe. Both are often criticized as outdated, inefficient, inaccurate and stone age. Notice that their continued use in the face of all criticism is justified by the same three word sentence, “It is reliable.” People who have held either one in their hands, stared at its metal parts and though about how they would need to count on it, will have some appreciation for that three word sentence. If I can teach you only one thing about experimental aircraft, let it be this: There is no characteristic more important than reliability. Anything you could get in trade for reliability isn’t worth it.

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Thoughts on ‘Alternative’ Carbs:

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It is my strongest recommendation not to use any type of motorcycle carb. This includes a Revflow, a Keihin, an S&S, an Altimizer, a Mikuni, a Harley-Zenith, and especially not a Bing. If I were required to list all the ways that a motorcycle or other non-aviation design carb could fail, I would have a long list. For example, the Bing throttle isn’t connected to the cable, and many CV motorcycle carbs have this “feature.” The two biggest failures  that I can name is  throttle systems that are operated by bicycle cables and the fact that most  motorcycle carbs don’t have any way in which you can attach a serious fuel line.  A piece of fish tank tubing and a hose clamp is not serious, and if it works on a Rotax 503 in a cowl-less pusher application, that doesn’t mean it will live in a sealed engine compartment in a traditional aircraft. Throw in that they have no mixture control, and often don’t fit where aircraft carbs do, and you get to a better understanding why there isn’t anyone saying how well the combination worked on the first 100 hours on his Corvair powered plane. My least favorite carb in this genre is the Bing. It has a tendency to lean out on long manifolds, and it will actually shut off if subjected to ram air. In 2012, we had a builder who insisted on using one and did $3,000 in detonation damage to his engine on the first flight. The same plane would have flown perfectly fine on a $500 Stromberg. I am sure the bystanders to this event were far more willing to see the issue as a Corvair problem than to understand that it was caused by a poor German motorcycle carb mis-applied to a proven engine. Carbs salvaged off snowmobiles, outboards, imported cars and lawn equipment are never going to have a good record on planes, and their advocacy is limited to people who wish to impress others with cleverness, but never actually impress people by going flying. Again, I don’t find it my responsibility to define all the ways that will not work for people who don’t wish to go with something proven. I spend my time trying to illustrate positive examples of how to do things that will work economically, but above all else, reliably.

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Thoughts on part #3601- Intake Manifolds:

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The Intake manifolds that we make for Corvairs evolved slowly over time and testing. Originally we made individual manifolds out of welded sections of mild steel tubing. We tested both 1.375” and 1.5” tubing, both on the ground and in the air. After a lot of evaluation, we went with the larger size from 2001 on.  In 2003, we started having the main tube of the manifolds bent by a CNC tubing bender as a single piece. This eliminated a lot of welded joints and gives the manifolds a much cleaner appearance. We looked at several different materials and selected thin wall 304 series stainless steel tubing. The primary reasons for this choice are that it is essentially immune to stress cracks when TIG welded and purged correctly, it remains clean on the inside and will not rust even if the aircraft sits for a long time in humid weather, and it is as light as an aluminum manifold because the aluminum would have to be made much thicker to have the same strength and crack resistance. After 15 years of continuous production, our manifolds still have a perfect track record.

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When first looking at the layout of the manifold, many people think that it will not have sharp throttle response, or the length of the runners will hurt the power output. A builder with a background in motorcycle racing confessed that he first thought of a steamship’s engine telegraph where the bridge swings a big lever on a pedestal that rings a bell in the engine room and makes a hand on a clock face point to the words “Full Ahead.” After he built his Corvair engine, he was surprised to find out that the throttle response on it was just as fast as a typical car. On aircraft, the limiting factor on how fast it can change rpm is the moment of inertia of the propeller assembly. On Corvairs, this is inherently low and the engine accelerates noticeably faster than other aircraft engines, even with a long intake tract.  Look at any modern car; designers are going to great trouble to make the intake runners much longer, not shorter. They are after more torque in the rpm range that direct drive engines fly at. A long intake tract doesn’t mean less power, and I am not sure where that myth started, but you can take a look at things as diverse as a tunnel ram with dual quads on a V-8 and see that even 7,500 rpm drag cars benefit from longer runners. But you need not be concerned with theory.

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I have years of dyno testing of most every type of intake length and carb configuration that conclusively shows that the length of the intake run has no effect on power output.  For years this was a favorite Internet debate topic among people who had never seen a Corvair turn a prop, but felt certain that the world needed to hear their impression of how it worked in their imagination. A number of these people also advocated putting the carb on top of the engine. I am going to flat out say that I have never found a single good reason to do so, and there are a number of very good safety reasons to have it on the bottom. I have seen people run every carb on top from Bings to Webers, and none of these installations worked nearly as well as even Bernard Pietenpol’s 1960s installations that featured tractor carbs mounted below the engine. I have seen more than one person plan on running an AeroCarb with a fuel pump mounted on top of a Corvair engine. Such a combination is virtually guaranteed to leak fuel onto the engine in operation. If a person is that interested in cremation, they should just find the professional service in the Yellow Pages and skip all the hassle of building a plane. I will not knowingly assist anyone who puts a carb on top of an engine or uses the leak prone stock Corvair mechanical fuel pump, and especially not in combination.

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There are always “experts” who claim that individual runners to each intake will make more power, that something is wrong with the offset intake pattern on the Corvairs intake log, or that the log should be removed. These are all myths that I long ago disproved with our dyno on back to back runs. In section 3700 look at the photo of Mark Petniunas’ EFI engine running on my dyno; it has individual runners and made no more power; the offset intake patter appears on many other aircraft engines such as Rangers and Allison 1710cid V-12s (good enough for P-38s P-40s and P-51Bs, probably good enough for homebuilts). The log part of the head is an important part of the mixture distribution, and it is structurally part of the head. If you mill it off you will weaken the head and blow the head gasket because the upper row of head bolts will no longer have a stiffener. Do not listen to anyone who suggests such modifications to the heads.

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We make several different manifolds for the Corvair. The most common is the 3601(S) which is the standard manifold for anyone mounting a Stromberg, MA3 or any other float type carb on their engine. This fits all the Zeniths, KRs, Tailwinds, etc. The second design is a 3601(E) which is the same manifold with the carb flange rotated 13 degrees forward. This is specifically made to serve Zenith builders who are putting a flat slide carb like an Ellison, Rotec or an AeroCarb on a tricycle landing geared airframe. The rotated carb flange provides clearance to the nose gear.  The 3601(C) manifold is specifically made to fit a Corvair into a Sonex or Waiex airframe using the Wesesman’s installation components. They have ones specifically for Panthers also. If you need further guidance, look at out parts catalog or give me a call or send a note.

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