Safety Alert: Excessively Rich MA3-SPA Jetting.

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. 


DATE and REVISION:  23 June 2017. – Original Safety Alert on this subject.


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.


APPLICABILITY:      Recommendation for inspection, MA3-SPA carbs rebuilt by D&G Supply


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


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”



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.




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.


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.


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. 


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.


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.


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.




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.





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.




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



36 Replies to “Safety Alert: Excessively Rich MA3-SPA Jetting.”

  1. This explains exactly why I crashed my Zenith CH-750 twice, thinking it was a carb ice problem.
    I corrected the problem with carb by adjusting the cable to prevent the carb from being in the full-rich condition

    1. Doug, I do not want to conclude that until I hear from Mac Morris, the current owner of your aircraft, after he has the carb internally inspected. BUT PLEASE NOTE: You didn’t ‘correct’ the problem by adjusting the external control, that only masked it. The only thing that can be called Correcting the problem is re-jetting the carb back to its original configuration. I emphasize this because I want people to understand that changing the exterior controls is not acceptable, the plane must run at >5,000’DA with the arm on the carb in the “R” position, on the stop. -ww

  2. William, I would like to compliment you on the professional tone of this communication. It is straightforward, clear, with valuable content. And, it certainly expressed respect and confidence to the builders, a significant morale boost to many of us. Definitely to me! Well done, sir. Thanks, Mike

  3. This goes counter to my experience with what I received from D&G. Mine was a to lean condition and was never rectified by D&G nor had talking with you provided anything but general clues. The Dyno testing, Venturi and jet changes seem to be working quite well now after 300 plus hours of flight testing. 28 degrees of full advance seems to work well also even though I’m using 100LL.

    1. Ron, Your plane, and your experience does not represent the fleet of Corvair powered planes, nor my nor Dan’s experience. Nor has your Dyno owner ever been PIC in a plane with a mixture control. It was not in D&G’s power to cure other issues your plane was experiencing.

      We have researched this safety alert very carfully before writing this, and I have identified a number of engines which ran great on the stock 10-4894 at Colleges, later flew poorly on overly rich carbs, then after jetting to stock specs, ran perfectly. I suspect that the one of a kind nature of your aircraft produced a different result which should not be used by anyone else.

  4. Hi William, Do you know the date D&G started jetting these carbs rich? I have a carb from them but I have not yet used. If I got it back from them after the date they started jetting them rich I will send it back, if you don’t have that info Ill just call them. Thanks for all you do and keep up the good work.

    1. David, I want to leave all the contact to direct communication between D&G and the people they sold the carbs to. Please call them for more information if your paperwork doesn’t specify stock jetting.

    2. Look at the inspection report if in the section above where it list parts used if it says nozzle and lists some numbers and then = approx. a prectange. then your nozzle was modified. We have been modifying these for about 2-3 years based on info that we thought was good feedback and has now turnout to be not so good let’s just say. tomorrow we will be working on a list of serial numbers I don’t yet know how complete it will be but we are going to try. The best thing you can do though is check your inspection report.
      The guy who most likely built you carb

    1. Ron, I am not in the business of rebuilding carbs, nor do I pretend to be. My own carb was rebuilt by D&G. They are an FAA certified Fuel System Repair Station, they have all the data, they are more than willing to work with builders who they sold a carb to. It isn’t my intention, nor responsibility to publish lists of internal carb parts for other peoples customers. Having a few part numbers, and a ‘friend’ who is a car mechanic who thinks he knows everything doesn’t make someone a repair station, it makes them dangerous, as they will inevitably try to dissuade builders from following this safety alert.

    2. Tomorrow we are going to work on a list of serial numbers. I don’t know how complete we can make it but we are going to try our best. The easiest way to tell is look at the inspection report if in the section above parts used it says some numbers and = approx a percentage then your carb has a modified jet.

  5. I asked D&G if my MA3 would be yellowed tag from him. He said no becouse he rejets them. This is why he stamps a C for Corvair after the model number on the data plate so it can never go back on a certified engine. So I would say if you have a C stamped on your data plate then it was rejetted.

    1. Paul, YOU ARE WRONG. Please read the last sentence on the safety alert, and understand it was aimed at comments like yours. The “C” designation on a Carb from D&G has nothing to do with the jetting, Both Woody Harris and Ken Pavlou have 500+ hours on MA3-SPA “C” carbs, and neither of them has rich jetting, so you are wrong. The “C” designation is no indication of jetting. There is no need, for you nor anyone else to attempt to “interpret” the applicability of this safety alert for any other builder. The method of compliance is simple and direct, and wrong comments like yours are a serious impediment to this being implemented. If you have made any comment like the one above on any internet discussion group, you may serious wish to go back and correct yourself right away. Red my comments to Ron to understand why you may seriously wish to avoid making incorrect statements which could be considered a recommendation, even when you are not selling anything to the recipient.

      1. William, The information that you provided in this safety alert was not or will not be retransmitted in any way to any other form by me. Per your request.
        I will be talking to D&G about my carburetor. I will ask him about the stamp again. Because he told me he had to stamp the data plate when he rejetts them so they would not go back on certified airplanes. There might be other reasons why he stamps them.

      2. Paul did you read WW post correctly?

        William, The information that you provided in this safety alert was not or will not be retransmitted in any way to any other form by me. Per your request.

    2. Actually the c is behind the part number. And in this case you will have a
      10-4895c. Which is basically an o-300 carb body’s with 10-4894 guts and works just the same as the 10-4894. So the “c” has nothing to do with the jetting of the nozzle. The reason this was done is so that years from now if someone wants to convert that carb back to a o-300 carb they can. This is coming from the guy who most likely built your carb if it has been done in the last 5 years at dgsupply

  6. “If the jetting cannot be positively verified as stock, then the carb should be returned to D&G for inspection.”

    The rest of the posting is background info. But the action item is the quote above. I do not understand how anyone can argue with that sentence or try and parse or interpret it. From a risk management standpoint, it is simple. Just get your carb checked if there is ANY doubt.

    Simple as that.

  7. Scott and WW


    I will be checking my paperwork tonight.

  8. William
    I was looking fwd to first eng run on the aircraft this week, but carb is on the way back to D&G as it was one that had been richened. I remember when speaking to Russ when ordering the carb that he mentioned enriching the carb. At the time I assumed he had discussed this with you or Dan. My mistake, I should have questioned him at the time. Thanks for the alert.

    1. Keith, Sorry about the hassle, but it was an honest error, and D&G has been sterling on being willing to correct this. Without making a drama of it, the data that was presented to them was from a one of a kind installation, where the people working on it ‘discovered’ the alleged need for this. I tend to say complimentary things on my website about people, and if D&G looked, nothing about the information suppliers would have raised an issue. I have worked with D&G for more than 10 years, but have never been to their shop, nor have I met Russ and his crew in person, I just know them by their work. Frankly, how they are covering this tells me more about their character than all the years without issue. It is just a simple issue to be corrected. Thanks for taking the information seriously. ww.

  9. Ok I just got done making what I think is a complete list. My dad should be emailing it to WW today and hopefully he can post it soon. 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

  10. William-
    I purchased my carburetor and it was shipped to me on 11/24/2014. It is jetted wrong. Anyone that either purchased a named carb since 11/24/2014 falls into the MUST CHECK category.

    1. Bill, I have just posted a link in the alert to a list that Russ sent me, it list the individual carbs affected. I appreciate your shared experience, but I want to emphasize that builders have to verify their individual carb. Your point is correct that anyone after your date obviously must check, but I don’t anyone reading it to incorrectly think that no carb before your date is in this. -ww.

      1. WW

        The link is not working for me…Yes I am a needy one

      2. Bob, yet again, I demonstrate that I’m not kidding when I say I am a troglodyte, have no computer skills, was kicked in the head by a pony at age 5, hit by a car at 10, and had a serious accident at 19 which left me with a two digit IQ. -ww.

      3. Scott,

        Thank you. D&G is top notch.

  11. Sent my carb to D&G on Monday and had it back by Thursday evening. Test run this morning. Excellent job by D&G.

  12. My ma3spa from D&G operates flawlessly right out of the box. I am getting 2775 static @ 32degrees full advance with warp drive prop set at 8 degrees. Mixture operates as it should and idle mixture needed no adjustment. I only needed to set idle speed screw about 1/2 turn. I think my carb was bought before the jetting change but I will definitely check numbers. This is excellent information. I am only the airworthiness certification away from first flight. Ironically, the 750 builder was getting flight training at Buzzair Flight Academy while I was there last week for transition training. He mentioned carb icing on the corvair and decided to go a whole other firewall forward route. These are the kind of things that give me an uneasy feeling whenever I mention to someone that I am using a corvair. Bad information gets out there and people believe it. It’s ok though, just the nature of the beast. I still believe that built properly, the corvair will serve well.

  13. William,
    Thanks for your effort on this matter. D & G was stellar! My carb is on the way back. Thanks again.

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