Please Read the Comments section for further information. Scott Romey in the comments is a technician at D&G. His information can be directly followed on this matter. Applicability now contains list of individual carbs.
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DATE and REVISION: 23 June 2017. – Original Safety Alert on this subject.
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SUBJECT: Some MA3-SPA carburetors remanufactured for Corvair builders by D&G Supply in Niles MI, were jetted excessively rich. While done with good intention, testing and operation has conclusively shown that the stock, original jetting for a 10-4894 model works on all displacement Corvair engines from 2,700 – 3,300 cc.
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APPLICABILITY: Recommendation for inspection, MA3-SPA carbs rebuilt by D&G Supply
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Below is a file, listing all the individual carbs believed to be affected by this safety alert. Any builder with a question should directly contact D&G rather than make an assumption
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From Scott at D&G: “I just got done making what I think is a complete list. All we ask is to please call or email us before sending the carb in. so we can confirm it has a modified nozzle and not waste time and money on shipping”
https://docs.google.com/spreadsheets/d/1NP6szGNgx4C9cXVRAbWVo0usHuQgHA77HeJtg6aP-fg/pubhtml#
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EXCLUSION: This does NOT apply to any MA3-SPA carb which is known to have original model 10-4894 jetting. NOTE: We have never sold carbs. I have just recommended models and suggested jetting and suppliers. Thus, any comment that starts with “My Carb came from WW” is not a factual statement.
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COMMENTARY: Over the last several months, I have gradually become aware that some Corvair builders utilizing MA3-SPA carbs rebuilt by D&G supply had excessively rich carbs. This prompted a survey of builders, revealing that a number of builders had excessively rich carbs, but had not spoken with either myself nor D&G. Without such contact, the scope of the issue was not previously known. Today, I believe we are speaking of 35-40 carbs.
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Dan Weseman and myself have always used MA3-SPA carbs with stock jetting on all of our Corvairs. My run stand, which has operated several hundred Corvair engines has a completely stock MA3-SPA on it. This exact carb was used for the extensive computerized dyno testing we did in 2015 at John’s Speed Shop in Jacksonville Florida. Dan’s 3.3L Corvair ran one test to 147HP, and the instrumentation and data logging showed that the stock jetting on the carb worked perfectly. Jetting requirements are not directly displacement nor output related. All displacement and output Corvairs with MA3-SPA carbs in my work and testing have been shown to run well with stock jetting.
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The erroneous rich jetting was generated by one builder in Michigan, and his mechanic, supplying ‘information’ to D&G, without speaking to me about our testing. D&G, mistaking the supplied ‘information’ as typical data, made other rebuilt carbs richer. This misunderstanding has now been corrected, D&G is absolutely willing to re-jet the carbs, and it is up to builders to do their part to make sure their carb is jetted correctly.
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If you are running your engine at a density altitude of 5,000′ or less, the engine should run without issue with the mixture set at full rich. If the engine only runs cleanly with the mixture pulled back significantly, this is an indication that the carb is probably excessively rich.
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This excessively rich condition is a safety issue for three reasons: 1) The engine will not make full power if it is excessively rich, 2) It will have a significantly higher fuel burn, it will have reduced range and duration. 3) in the event of a go-around, pilots are taught to instinctively push the throttle carb heat and mixture full forward. If the plane will not run correctly with the mixture full rich, it will be an issue just when the pilots full attention needs to be on flying.
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Builders should not assume their carb is jetted correctly without verification. I recently spoke with a builder who was selling the Corvair he had removed from his flying Zenith after about 15 hours. He never called to discuss the issue, but he was convinced that he had been experiencing “Carb Ice” , and claimed that he knew this because when he had the throttle pulled back for some length of time, the engine ran rough. He never tried pulling the mixture, or calling, he just decided to remove the engine and replace it with a fuel injected one. I have spoke with the current owner of the engine, and can say the issue was simply an excessively rich mixture. The plane was not experiencing carb ice at all. It just needed the carb re-jetted. Instead, it got a completely different engine. Calling us when you have an issue can save a lot of time and money.
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SUGGESTED ACTION: I highly recommend that all Corvair engines with MA3-SPA carbs verify they have stock jetting. Carbs rebuilt by D&G came with paperwork which indicates the jetting. If the jetting can not be positively verified as stock, then the carb should be returned to D&G for inspection. If the carb was jetted richer than stock, this will be corrected by D&G. I have spoken with the owner on this, and he is more than willing to rectify this issue for builders. There is no excuse why any builder would continue to operate an excessively rich carb. Already having 10, 20, or even 100 hours of operation with excessively rich jetting without does not justify their further use without correction.
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http://www.dgsupply.com/contact-us
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This is a “Safety Alert” and I am issuing a “Suggested Action” because Corvairs are experimental engines, and as such, do not have Airworthiness Directives and Service Bulletins in the same form as certified engines do. I cannot require any builder to take any action, I can only appeal to his better judgment by making a serious recommendation. Airworthiness Directives are only issued by the federal government, and Service Bulletins are issued by certified part manufacturers, thus the difference in the Safety Alert.
This said, I appeal to builders to follow this recommendation. The most frequent form of push back on suggestions of this kind is a builder who is myopically looking at his one plane and making a conclusion based on his impression of his own plane. Conversely I get to see all the data, understand the extenuating or aggravating conditions, I had world class training in statistical decision making at Embry-Riddle, and I always further consider what still works, not just looking at what broke. I am not a genius, but for the above reasons, my recommendations on Corvair flight engines carry more weight than those of one guy with a flying plane, even a well intentioned one. We don’t have to speak of opinions of internet personalities that have no direct personal involvement nor experience with flying Corvairs.
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DISTRIBUTION: I ask that this information be shared with others who personally involved in building a Corvair flight engine. This should be done just by people who have read and understood the information themselves, who also are Corvair builders. For this safety message to have efficient, accurate and timely distribution, it should not be forwarded in part, nor by anonymous sources. I issue Safety Alerts very infrequently, and they need to be taken seriously. Any impediment to their accurate transmission to builders is an act contrary to the safety of builders.
William Wynne
WilliamTCA@flycorvair.com