C85 Conversion Complete!

[N96337]

I don't know... it's only worked for 73 years.... I think I'll take my chances. Last time I went through it, I put in a new needle and seat.... wasn't very expensive.
John

[astjp2]

For what it's worth, core value for the Stromberg is about $300 when exchanging for a marvel. I was lucky to have a buddy with a marvel core laying around.

Are you ready for toe brakes yet?

[3Dreaming]

Are you ready for toe brakes yet?

Why? I have over 7500 hours flying time, and around 1300 in airplanes with heel brakes. Personally I see no reason to switch, they work just fine.

[Scott]

I don't know... it's only worked for 73 years.... I think I'll take my chances. Last time I went through it, I put in a new needle and seat.... wasn't very expensive.
John

exactly, the Stromberg is a simple reliable carb, and because of that I think they end up in service without much attention for a long time. Eventually the throttle shaft wears to the point where odd things start to happen that get blamed on the absence of a throttle pump or the "innovative" mixture control (plus perhaps a little fear of the unknown).

I salvaged mine by machining .005" off the throttle shaft and machining undersized bushings to suit. It already had the steel float valve so all I had to buy was a gasket kit and new screws. (I can't imagine paying, or charging, $900 for this work)

Works fine, including the mixture control.

[N96337]

Amen, Scott! I'm not saying the Marvel wouldn't be great!! I'm just saying that my money would be much better spent on gas in my opinion, and use what is working fine and has for many years!
John

[PA1195]

At this stage of the discussion cold weather ops typically gets injected...it's a yes, but what about in this situation argument. Under certain regimes transition from low to higher power is aided by an accelerator pump device in the carb. A few million road and other vehicles that require something beyond what a stationary power plant or farm implement needs for example. I also suspect a heavy prop - metal vs the traditional wood - adds resistance to and can slow engine spin-up.

No doubt Strombergs work but there are some local old timers I've talked with that flew them pre and post WWII that developed survival techniques prior to the Marvel's pump. I don't recall any that missed the Stromberg if the situation called for a quick power recovery. I know two that were left with damaged planes that refused to fly in the cold when needed. Warm ops...well not so risky I was told.

I had a Stromberg on both my Taylorcraft 85's. Truly both were the Prince of Cold Weather Silence until I installed a Marvel, but that may have been just my lack of technique.

Gary

[Scott]

I understand the assumption that the absence of an accelerator pump equals no enrichment as the throttle is advanced, but this is an assumption not a fact.

Fuel injection systems have no throttle pumps but the mixture is enriched when you advance the throttle. This is achieved by sensing air pressure/mass at different points in the induction system.

Believe it or not the Stromberg does the same thing. It uses ventury pressure verses ambient pressure to increase/decrease fuel from the main jet. At the point of throttle advancement the mixture is richer and as ventury pressure changes mixture gets leaner. Ventury pressure is also used to reduce the head pressure in the float chamber which causes a leaner mixture. The mixture control varies the amount of ventury pressure applied to the float chamber.

All this to say that if the stromberg is the correct part number for the application, and it is properly set up and maintained, there are no issues.

I flew my aircraft on skis at temps down to -25C (with a metal prop) and never had a dull moment! At that time the mixture control was wired full rich. Since I rebuilt it I use the mixture control just about every flight and other than the fact that a little extra patience is needed, it works just like any other mixture control (except no idle cut off).

As I've learned more about the Stromberg, I've become more impressed with it's uncomplicated yet sophisticated design. Somebody did their homework 75 years ago!

[PA1195]

Thanks Scott for absolute facts and challenging a 45 year personal and extended to others experience with the above theory. Without sarcasm intended respectfully I can now inform that Marvel carbs are not better in cold temps or otherwise. In Alaska Strombergs are replaced when able and where -25C is still warm. But seriously if you like them run them but I assume you're well insured. Few still do in colder climates and that includes millions of road vehicle owners without patience when needing response. This is one reason why Taylorcrafts as equipped are selling for less than value compared with others.

Come on up someday and we'll go ski flying in the cold. I'm open to actual new experience.

Gary

[PA1195]

Another issue in colder weather is fuel condensation in the induction system. Depending on air and engine temps, in-cowl airflow, and baffling fully or partially atomized fuel in the cylinder intake air can condense and attach to nearby cold metal. When that happens the air fuel mixture goes leaner than desired and proper running can become a problem.

I and others have had that happen primarily on initial startup and on descents to landing. Carb heat can help keep the fuel from condensing to a point, but low power produces less heat which eventually dissipates and the help diminishes. There are lagging /covering kits that are intended to prevent overcooling of the induction tubes and oil sump but typically the induction spider and cylinder intake elbows remain exposed to cold air.

No carb is perfect and in reasonable climates I'm sure a properly maintained Stromberg works as well as intended.

Gary

[Kerbs]

I wasn't looking to debate the merits of which carburetor. Just simply stating in my case, I am enjoying the marvel carb more than the stromberg I had previously. That said, I would not have replaced the stromberg on my A65. The only reason I replaced it on the C85 was because I needed a carb and elected to go with an overhauled Marvel vs tracking down and overhauling a stromberg. Obviously strombergs work, these planes have been flying a long time on them, a lot with little maintenance to the carb over the years.

[Scott]

Another issue in colder weather is fuel condensation in the induction system.

I and others have had that happen primarily on initial startup and on descents to landing. Carb heat can help keep the fuel from condensing to a point, but low power produces less heat which eventually dissipates and the help diminishes. There are lagging /covering kits that are intended to prevent overcooling of the induction tubes and oil sump but typically the induction spider and cylinder intake elbows remain exposed to cold air.

No carb is perfect and in reasonable climates I'm sure a properly maintained Stromberg works as well as intended.

Gary

Interesting. I have not heard about this before. Is this a mogas thing or 100LL as well? The latter of course being designed to include operation at altitudes where temperature is always in the low double digits. Our engines also have the induction system in the the relatively warm zone of the cowling i.e. downstream of the cylinders and their dissipating heat. The lower pressure in the induction system would also tend to lessen the likelihood of condensation of fuel.

Also I was under the impression that gasoline does not really vapourize in an induction system but "atomizes" i.e. the state of the fuel-air mixture is tiny droplets of liquid suspended in air. So is this actually condensation of gasoline in the induction system, or some form of coalescance?

I can understand water condensing out of the air (and fuel if it has ethanol or other contamination) in the induction system, this is the essence of carb icing, but can't really get my head around condensation of gasoline (which has a flash point of -43C) and is mostly in the liquid state already. Would like to understand more if you can elaborate or point me to and article about this.
Thanks
S

[astjp2]

In the process of the gas being discharged out of the nozzle, it cools the intake air and when it gets too cool, the fuel droplets fall out of suspension, carb heat helps reduce this phenomena. Lycomings have their induction air go through the oil pan, it make for a consistent air charge and therefor less issues when flying in cold weather compared to a small continental. Tim

[PA1195]

Not intended to drift Kerb's thread, but here's some disconnected comments to agree or disagree with.

Warm climate/engine and cold climate/engine ops require different air/fuel conditions. And from the automotive world but could logically extend to aviation > https://www.waybuilder.net/sweethave...Num=2&modNum=3

Here's some further info on methods to support the phase change of fuel from liquid to vapor: https://www.hotrod.com/articles/unde...is-hard-to-do/

Most would agree from experience that cold engine components and fuel require a richer fuel mixture (even if only temporary) to start and run properly. Chokes, primers, injectors, and accelerator pumps provide the excess fuel as required. There is also a transitional lag in carburetors between air flow and fuel flow...it takes time for fuel to be discharged into a rapidly increasing air stream if the throttle is quickly opened. As a result throttle movements in flight should be measured unless additional fuel can be quickly available. Alternatively, warm or heated induction air creates a less dense/lighter weight air which alone creates a richer mixture. We add carb heat to both discourage carb icing and maintain that richer mixture when needed.

For liquid fuel to provide combustion it experiences two transitional stages-initial raw fuel to fine particle atomization and then vaporization and mixing with the intake air (the optimum gaseous air/fuel mixture of around 12.5:1 +-). Raw fuel burns poorly when cold as it's the vapors from the fuel that quickly oxidize/ignite. As ambient temps lower, cold unheated intake air gets heavier while fuel flow and weight remains relatively constant. That's controlled by the number of the carb's air mixing and diameter of the fuel jet orifices. Then there's fuel vaporization rate controlled through seasonal blending...more for auto fuels than aviation which is stable.

As air temps decline the engine progressively runs leaner as evidenced by increasing EGT and eventual loss of power as the A/F ratio exceeds optimum and goes lean. As temperatures chill, carbureted engines typically require larger orifice jetting to maintain the desired air/fuel ratio and performance, or preheated air is added. Temperature sensing fuel injection can be designed to compensate.

So how does all this relate to engine hesitation or potential stoppage in cold climates? Any time the induction system is excessively cooled during a power-reduced descent there's a potential for a lean air fuel ratio condition. Continental engines without the oil sump heat provided to the induction system by Lycomings are more susceptible. Ensuring the idle mixture is set rich for expected air temps (results in the approximate +50 rpm rise at idle cutoff we set) and having an accelerator pump available to quickly add fuel can minimize a power response problem in my opinion and experience.

Gary

[N96337]

Mine with the Stromberg was persnickity to start when it was really cold. That being said, I always figured it was a sign that it was too cold for me to be out flying. However, I don't have the long extended extreme cold spells that Gary has to deal with on a regular basis. I'm kinda a fair weather guy. If my circumstances were different, I'd probably go a different route if it gave me trouble.
John

[PA1195]

As I age my low temp ops have decreased. I also fly less now as I've had almost enough of unexpected adventures. Things can happen quickly in real cold. Previously I'd fly a pre-heated FI engine and cockpit down to -50F but was careful about power applications. Carbed Lycomings would run ok for me to -40F but maintaining oil and cylinder temps were a concern. These small Continentals have me wary below -20F as they never really warm up and maintaining adequate fuel flow can be a challenge. Carb heat in cold can be used if carb icing is monitored. I've had cowl flaps and cooling air baffling on the FI and carbed Lycomings but not yet with the small Continentals.

Another thing is that Marvel carbs with accelerator pumps offer adjustable discharge volumes. The link from the throttle arm to pump piston can be altered by selecting one of three connection holes. The max discharge hole #3 is usually selected, but in warm climates less can be set.

Gary