Continental A65 Mixture

[Smithfield Slim]

Re: Continental A65 Mixture

Back when I had an A65 on my bird, the best I could do was 12,000' ASL. I coughed and sputtered over the Uinta Mtns. After I put mixture control parts in my Stromberg, I went right up to !8,000', where I gave up because my feet were freezing. i.e. The mixture control worked great , but the heater didn't........ Don't try this at home.

[Jim Meeker]

Re: Continental A65 Mixture

Cpirrmann
As I understand it, the mixture control on the Stromberg Carb is really an altitude adjustment control (you are adjusting the float level). That is why when you pull it all the way out on the ground it will not starve the engine of fuel enough to kill it, it will just run rough. Consequently it is not effective unless your altitude or density altitude is high enough above sea level to require an altitude adjustment for the fuel air mixture. My experience is that you have to be at least 5,000 feet for it to make a difference. If you never fly above 5,000 it won't do much, and it is my understanding that is why so many are wired shut back east. However, out west, where I often fly at 9,000 + ft it can make the difference of 150+ rpm and reduce fuel burn from 4.2 to 3.8 gal per hour. It also appears to run best with the throttle wide open (full throttle above 5,000 gives me approximately 2150 rpm). Mine does not leak but if I am done flying for the day I usually pull the fuel shut off and burn all the fuel out of the carb on shut down. Rob Ray (aka> > Smokey F16 Guard and SW pilot, he put out the Taylorcraft calendars back in 1997) once talked to the designer of the carb and sent me an email on the design principle, I will copy it below:

The first email was in 11/18/95
“About the mixture control: I ran into an old gentleman (geezer) who had been flying small continentals since they were built. He talked to the Stromberg carb guy personally who designed the mixture control for operating the A-65 above 5,000 ft MSL. He said the original instructions went like this. When operations above 5,000 ft are necessary, open the throttle (full) and allow the rpm to stabilize. Slowly pull the mixture control out until the rpm slightly decreases. (very slight change on mine) Then push control in to maintain rpm. I have found through experimentation on many trips that above 5,000 I pull the control out about half of what I use above 10,000 which is all the way out. The old guy said to run the A-65 wide open above 5,000 ft and if your rpm was higher than 2350 get a new prop. (or re-pitch the old one). The key is rated rpm. The A-65 is rated 65 hp at 2300 rpm. You can only run it like that above 5,000 ft, so the secret is to fly high and leaned out and wide open to get total performance. 5,500 seems to be the best in my experience.”

11/30/95
Follow up email where I queried about a friend who told me his practice was to lean mixture even at sea level in a C172 and where I asked a few follow up questions to the message above. “About leaning: I grabbed all of my lycoming and continental service bulletins and talked to my resident ‘expert’ and compiled this info for you. Lycoming
engines require ‘aggressive’ leaning. The book recommends leaning for peak egt even at sea level. (when I towed banners with 180 hp Scouts we always leaned as it brought our fuel consumption down.) As far as C-172’s go, all of them have marvel schebler carbs on them. (idle-cutoff capable) Continental recommends full rich on climb on all of their six-cylinder engines regardless of altitude unless %rpm is a problem. 172’s came out with Lycoming engines after 1973 so maybe the one Mike rented had a lyc up front which would definitely require leaning at sea level. A lot of people still lean out continentals on climb, but cylinder head temps could cause damage if not monitored. So what does this mean to us yahoos who operate little A-65 continentals with mixture controls? According to the late, great Bud Miller who lived up here (South Dakota) and flew Tcrafts and Luscombes starting in 1935 and was a 40+ year A&P he said: the bendix-stromberg carb (one we have on A-65) is the finest carb out there. It atomizes the fuel better than the Marvel carb and has less moving parts. The mixture control was designed by a bendix engineer who later designed the first fuel injection system for light planes. Yes you can pull it out below 5,000 ft msl and yes it will work, but only slightly. The difference is that the Bendix mixture changes the atmosphere pressure of the floatbowl (highly efficient) to lean the mixture, where the Marvel meters the fuel directly. Below 5,000 msl the atmospheric pressure change is small, but there none the less. Extremely small movements produce big rpm reductions below 5K so use it sparingly. Used correctly though, it can cut your fuel burn a lot. Bud also said that the Bendix engineer designed the venturi of the carb to be almost “ram air” efficient with the throttle wide open. In other words, the less blockage in the throat, the better, so go high enough where wide open is the best setting. Hope this helps
Jim

[VictorBravo]

Re: Continental A65 Mixture

I wonder if Grace Huntington had a mixture control back in 1940 when she flew her T-Craft to an altitude record of 24,000+ feet!

I don't think they had JATO then!

Flying in the right part of a Mountain Lee Wave will beat a mixture control (or even JATO) any day

[Tom G]

Re: Continental A65 Mixture

I wonder if Grace Huntington had a mixture control back in 1940 when she flew her T-Craft to an altitude record of 24,000+ feet!

I don't think they had JATO then!

[NY86]

Re: Continental A65 Mixture

BTW, I saw an e-mail to Ron W. in which Neal gave Ron permission to use his Stromberg material; he sent the same e-mail to me, for permission to share it with the Taylorcraft group when we were with Topica.

Yeah, he doesn't mind sharing, but he has told me that he prefers folks link to the Cessna site as that's the only place where he keeps things current. I know at one point he was a little peeved with someone for proliferating copies indescriminately. Anyhow, I always refer folks to the Cessna site, that way they get the most recent version.

[larrysmith1016]

Re: Continental A65 Mixture

Yeah, Mr. NY86, that's Neal, a treasure trove of information. Thanks for the link; most readable and helpful!

BTW, I saw an e-mail to Ron W. in which Neal gave Ron permission to use his Stromberg material; he sent the same e-mail to me, for permission to share it with the Taylorcraft group when we were with Topica.

[NY86]

Re: Continental A65 Mixture

The files on the fly baby site are "bootleg copies." The latest versaions are at the Cessna 120/140 site

[larrysmith1016]

Re: Continental A65 Mixture

there is a fellow on this forum who is an expert on Bendix Stromberg carburetors, and he has asked me to help him write up some notes and instructions on them. I will be glad to do so, as soon as he and I can set aside the time to do it.[/QUOTE]


By all means you should do so. I have rebuilt several but don't enjoy it. I have 2 more to rebuild and dread it. Some interesting and helpful material on Strombergs may be found on Ron Wanttaja's Fly Baby website. The author's moniker is Cougar, and he's from Sacramento, iirc. Using Cougar's pdf files, I made one of those neat little tools for measuring the fuel level in the float chamber and it works well.

Getting the shims under the seat just right is a trial-and-error operation and a pita.

[NY86]

Re: Continental A65 Mixture

I'd like to think I have a few good years left, too...

[VictorBravo]

Re: Continental A65 Mixture

I cannot speak for him, and he has more than once told me that he is not very interesteed in rebuilding too many of these old carburetors anymore..... BUT, there is a fellow on this forum who is an expert on Bendix Stromberg carburetors, and he has asked me to help him write up some notes and instructions on them. I will be glad to do so, as soon as he and I can set aside the time to do it.

[cpirrmann]

Re: Continental A65 Mixture

Or some of us better learn how to work on the 'older' stuff. Hey anyone interested in holding workshops?

[taylorcraftbc65]

Re: Continental A65 Mixture

I have noticed that when I fly at 8 to 10 thousand feet, out here in the desert in the summer, I get about 50 RPM better with the mixture control set leaner. I also have MUCH cleaner plugs, and yes, it stretches out my range too. The only reason that I will probably go to an MS carb at some date is that the only person in the area who knows how to work on the originals is getting very old, and talking about retiring soon. When that happens all of us flying the old stuff will have to choose between letting someone who has never even SEEN one of these carbs learn on ours, or go with something that they are comfortable working on. Brie

[larrysmith1016]

Re: Continental A65 Mixture

A properly operating Stromberg mixture control may get you an additional 50 - 100 RPM at 8 - 10,000 ft. More likely it'll just cut a gallon or so off your burn rate. Does this mean it's junk? I don't think so...

Q: Why does my plane perform so much better now that I have this Marvel-Schebler carb?

A: Because your wallet is so much lighter.

TMSAISTI[/QUOTE]

I use a mix control on a Stromberg here in WNC. I don't have any fuss with it, and you CAN use it to shut off the engine. Run the engine up to 1500 rpm then pull out the mix control, then firewall the throttle. Your A-65 will shut down. Not recommended, though.

[NY86]

Re: Continental A65 Mixture

Do as everone has said,wire it full rich or as Forest said plate it.

If you "plate" it, contact me. I'll give you something for the parts you remove!

[Karl Rigdon]

Re: Continental A65 Mixture

The Stromberg mixture control is known as a back suction type. The mixture contol is used to reduce the pressure in the float bowl by using the lower pressure in the venturi. This will reduce the pressure across the main jet therefore reducing the fuel flow. It was never ment to be a idle cutoff. Never was real effecive. Do as everone has said,wire it full rich or as Forest said plate it.