MA3-SPA Test Runs.

Builders,

In the last week I have been running several back to back test of two Marvel MA3-SPA carbs.  The Carbs are mechanically identical, but have two different histories.

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Above, two MA3-SPA carbs, perfect for Corvairs. To be correct, they must be, as specified in my manual, part number 10-4894, or the exact equivalent. And that doesn’t mean another MA3.

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If your aircraft plans say the spar is to be made of Aircraft Grade Sitka Spruce, you can’t use white pine from Home Depot; If you plans say the longerons in your plane are 6061T-6 Aluminum, you can’t replace them with screen door material from Ace Hardware; and if you are building a “WW Corvair” , you can’t just use any MA3 because you found out the right one cost more than wanted to pay.

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Good News: the 10-4894 is the most common of all MA-3’s accounting for 50% of total production.  Once set, they hold their adjustment and do their work  a very long time. Look at the two carbs above, the silver one has been used on my test stand nearly 20 years. It has run 100’s of engines, you have seen countless videos of it starting brand new motors in one or two seconds of cranking……I have never done any work to it, and it has never been overhauled, and the serial number indicates it is as old as I am.  This is an example of a well designed machine.

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The black carb pictured is from my personal aircraft. It was rebuilt by D&G fuel systems about 6-7 years ago, and I paid the same $600 every other builder pays. In very carefully instrumented test runs, this carb ran perfectly, even on Justin Peters’s 3.0L motor and on Mark Borden’s 3.3L . The carb does not have to be re-jetted to do this, it does it all on its own, because it is an excellent design.

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For more info on carbs, look at this: Corvair Carb Reference page for 2020.

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WW.

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