Stromberg richness

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MontanaGN1
Posts: 4
Joined: Mon Jan 22, 2018 9:25 am

Stromberg richness

Post by MontanaGN1 »

Hi Everyone,

I made the first flight of my GN1 in August and got about three hours in before fall weather set in. It sure was fun! I look forward to more flying in the spring.

I have an A-65 Continental engine and was expecting the Stromberg to run rich. Sure enough, it runs quite rich, and leaves carbon deposits on the gearleg. All flying in this area of Montana is done at 4000+ feet, up to about 6000 ft. in this airplane. Maybe this would not be an issue at sea level but at this elevation it certainly is. We also have significant density altitude here, as well, in the summer. This Stromberg was set up by the book with float height as called out in the manual. It is also the correct dash number for this A-65 engine.

Has anyone had some success leaning up the rich condition with either a float height adjustment or installation of a different main jet?

Paul Gordon
Helena, Montana
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taildrags
Posts: 436
Joined: Tue Mar 07, 2017 10:39 pm

Re: Stromberg richness

Post by taildrags »

Paul; I'm assuming that your Stromberg doesn't have a functioning mixture control? The NA-S3A1 carb was designed with a mixture control; the -S3B was blanked off. Some of them have the mixture control 'guts' removed and a blank-off plate over the place where the mechanism goes, while others simply have the lever wired at full rich. If yours has the guts still in place, you can work with it to improve your mixture at your altitude. If you'd like to discuss it off-list, email me at taildrags@hotmail.com , but there are resources out there for mixture adjustment on Strombergs. If you read the ops manual for airplanes that were certified with the control (Cessna 120/140-?), the book will say not to adjust the mixture on them below 5000', but there is no logical reason to that. Hearsay has it that people have killed the engine trying to adjust the mixture while close to the ground, but that's no excuse in my opinion. If you know how the control works and you use it correctly, it's there to be used.
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MontanaGN1
Posts: 4
Joined: Mon Jan 22, 2018 9:25 am

Re: Stromberg richness

Post by MontanaGN1 »

Hi Oscar,

Thanks so much for your reply. Yes, I have A NA-S3B and the mixture control is totally blanked off. I researched locating all of the bits in the mixture control assy and I found that they are difficult to find, overpriced, and that it probably would not work very well anyway. So, I think I will be faced with adjusting float level incrementally. I have quite a bit of related literature and will pore through it a bit more. I just don't want to reinvent the wheel. I will report back when I have some new thoughts.

Even on my O-320, I never use full rich. It has to be a cold day before I get close to using full rich on that engine.

Ciao,

Paul
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taildrags
Posts: 436
Joined: Tue Mar 07, 2017 10:39 pm

Re: Stromberg richness

Post by taildrags »

Paul; the Stromberg is a relatively simple carb as far as number of parts, but it's a very clever design. Looking at the fuel and air passages and how each of them comes into play in various stages of the engine's operation, I'm not quite sure how adjusting the float level will change the mixture that the engine sees, but I'm very curious to hear the results of your experimentation with it. I will say that on my airplane at least (A75 engine), adjusting the float level is not a trivial matter. I safety-wire all the fasteners on the carb including the screws that hold the two halves of the body together, and it's nearly impossible for me to get the carb open without pulling it from the intake manifold. That takes a while too. Then once it's off the engine and cracked open, the float level is adjusted by using different thicknesses and combinations of gaskets by 1/64" increments under the float needle seat. Every time you change the float level, you have to go through the whole process in reverse and button the plane back up to try it out. It requires care and patience to get all the parts and pieces back in place and everything properly secured each time, so good luck-!
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taildrags
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Re: Stromberg richness

Post by taildrags »

Paul; if you're going to open up the carb, that would be a good time to look at the main jet. Take a look at the comparison table below that shows the jet sizes for the different engine displacements. The A65 takes a #49 jet (the number should correspond to the same numbered drill size, 0.0730") and if your carb was ever run on a different engine, it could be any one of the other jet sizes in that bunch. The #45 is 0.0820", or 9 thousandths larger orifice than the one that should be in a Stromberg on an A65. Also, don't take it for granted that just because your jet is stamped as a #49, that it actually is, because many, many people and shops have drilled them out either so that they can run on a different, larger engine or "just because" they think it'll buy them more power. If you don't have numbered drills in that range, go to a machine shop or find someone with numbered drills and check the orifice size. If your jet is good, that will be an easy "no, that's not it" possibility you can eliminate. And if you do have a larger jet and need the smaller one, I just looked at Aircraft Spruce and they are listed as $12.50 for the one for the A65... very reasonable.
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Oscar Zuniga
Medford, OR
Air Camper NX41CC, A75 power
tom kreiner
Posts: 62
Joined: Sat Feb 25, 2017 9:49 am

Re: Stromberg richness

Post by tom kreiner »

Guys,

Oscar has outlined some very good info in his posts, and I'm adding just a few additional notes.

As stated, the Stromberg carb is typically wired in the full rich position, and according to a few old timers, that’s because the Aircraft Sales guys never thought anyone would fly above 5000 ft, and that leaning wouldn’t provide a tangible benefit. While the attached article was written for the C120/140 group, the same applies to all of the A series engines using the Stromberg carb. As the article attached explains, the sales guys were wrong.

Anyone involved in the recent discussions regarding lean of peak operations will also know that you want to lean the engine properly whether the density altitude is located at sea level with 100° days or in the mountains with 75° days. Proper leaning will result in not only better economy, but cleaner internals, combustion chamber, and longer engine life.

Since we are involved in experimental aviation, you may modify a main jet by filling the orifice with solder into which you have placed a number 50 drill. (Shank end in the solder.). After cooling, Re-install this in your engine and see how it runs. If too lean, simply drill out to number 52 and try again. This process would be repeated with larger drill sizes until you have a properly leaned engine at your altitude. The best way to determine whether it is properly leaned is to observe the spark plugs and see whether they are sooty or chocolatey brown. At your altitude, you should shoot for slightly rich, i.e., black, but neither wet with fuel, nor sooty, when full rich, and capable of leaning using the mixture control at altitude. Per the article, the mix control on the Stromberg doesn’t work quickly; you'll need to be patient while leaning with this carb.

One way to determine the proper richness when at ground level is to pull carb heat full on... engine must NOT die due to excessively rich mixture. Needless to say, all testing should be done on the ground prior to flight...

In the past, I have done this very successfully on several engines ( I lived three years in CO). For best long-term results you would want to ensure that you have a solid piece rather than a soldered assembly. Don’t worry about the Solder melting, if the carburetor gets hot enough to melt the solder - which is immersed in gasoline - the whole airplane would have already burned up about an hour hour previously!

Take a look at the article I've posted and when done, let us know what your results were.
Attachments
stromberg_mixture_secrets.pdf
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tom kreiner
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Joined: Sat Feb 25, 2017 9:49 am

Re: Stromberg richness

Post by tom kreiner »

Oops, The first drill to try should be a #54, , then stepping up in size to make main jet richer. After cooling, twist the drill with pliers, and pull out; this will leave a smooth orifice.
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taildrags
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Re: Stromberg richness

Post by taildrags »

...and of course, numbered drills go in the opposite direction of what you'd expect. That is, a #45 makes a bigger hole than a #50. Tom, I had not thought about the solder trick but that sounds like a reasonable way to start leaning the mixture.

Back when I used to do a lot of deer hunting, we would drive up from south Texas to the San Juans (Pagosa Springs, CO... elevation 7,126') to hunt mule deer. My dad's Chevy Suburban with a big carbureted V8 could barely pull its own weight up some of the logging roads we took it on, because it would sit there chuffing these big black clouds from the tailpipe as it missed and staggered and hit on 6 or 7 cylinders most of the time. Too rich! A guy at the shop in town knew the trick to adjusting the mixture for the altitude, at which point the vehicle pulled much more like it was supposed to with that big engine.
tom kreiner
Posts: 62
Joined: Sat Feb 25, 2017 9:49 am

Re: Stromberg richness

Post by tom kreiner »

Forgot to mention...solder needs to be rosin core to adhere to brass, but not to steel drill.
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