Ongoing Carburetor testing.

Builders,

The previous story covered updating the aluminum pushrod tube installation in my own personal Corvair engine. This was half of a particulars day of testing. The other half was to run the particular NAS-3A Stromberg carb pictured below. It has a different set of jetting in it, and we are working to fine tune it, and add that set of data to our carb knowledge.

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Strombergs are a traditional carb, not only for Corvairs, but for US light aircraft in general. The have a long track record of very good service. The particular one has a variation on what we have previously done before, and thus a test run was in order.

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Above, freshly overhauled Stromberg, running on my 3,000cc Corvair. The Fuel filter is an Earl’s unit available from Summit Racing, it has an accessible element and -6 AM male fittings on each end. My test stand has had one for years, and I also have one on my plane. Be very careful not to install it in a plane in a position where it could trap water.

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The photo doesn’t quite capture it, but the jetting or setting was on the rich side. Under some circumstances, it was producing visible black smoke. Look at how dark the tailpipe is. Keep in mind this is running on pure unleaded car fuel.  The Exhaust piped on my test stand have had 18mm threaded ports in them for the last 10-12 years, and I have used them with a wide band O2 sensor to know the actual air fuel mixture going to the engine. That is the next step in gathering data here.

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This was the afternoon on November 17th at our airport in Florida, still pretty green down in the sunshine state. The season slowing down with the approach of the holidays and the arrival of cold weather up north, we will have many afternoons to test ideas and parts in the coming months.

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Wewjr.

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10 Replies to “Ongoing Carburetor testing.”

  1. William,

    Coincidentally, I have been trying to determine the jetting on a NA-S3 in order to build a “Super Stromberg” as you and Dave Vargesko developed several years back. In looking at the Stromberg jet sizes for their 1 3/8” venturi carburetors used on C-90 and C-85 engines, as best as I can surmise, a Super Stromberg would be built with a #44 main metering jet and a #60 main air bleed jet. I am interested in seeing what you determine through testing with the O2 sensor to be the optimal jetting and if I am correct.

    Like another poster, I am interested in the downdraft Ford carb, as well. Even though it may perform similarly to a Stromberg it seems to me it would be less expensive to purchase.

    Doug Wright
    Stillwater, OK

    1. Doug, Where is this topic being discussed, because after I wrote the story, 3 people called or emailed Dan questions about this, and its too coincidental so Im guessing there is a discussion on this I’m missing? Glad to share the information, but I would like to know who its going to. In the last 3 years we have had a lot of difficulty with overly rich jetting, all brought on by an ‘Internet expert” who started a large mess which did a lot of damage to the good name of Corvairs.

      1. William,

        If this topic is being discussed elsewhere on the internet I am not aware of it. Your blog, the Matronics Pietenpol forum and Pietvair.net are the only other sites I visit. I have not been on the latter two in the last few weeks so it may be being discussed there. Don’t know.

        This post about Stromberg jetting is not what piqued my interest. I have been researching this topic the last week but had not read this post until this morning. On my part it was, in fact, coincidence.

        Doug

      2. Thanks Doug, I plan on following up with more comparative tests and an examination of the specific jetting in the next 10 days. Keep following, I’ll share the results

  2. William,

    Now that I think about it, the other Corvair related site I visit is the Facebook Pietenpol group. I don’t remember this being discussed there and can’t imagine it was in that most of the topics on that page are technically unsophisticated. Why those folks don’t use the wealth of information on the Matronics site is beyond me.

    Doug

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