Mixture Control Indicator

Discussion in 'Half VW' started by N8053H, Aug 17, 2013.

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  1. Aug 17, 2013 #1

    N8053H

    N8053H

    N8053H

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    Using the Zenith Carb on my 1/2 vw that has in cockpit mixture control. This carb uses a knob you turn. The problem one has you have no idea how many turns open or closed you are. I would like to make some sort of slider style indicator that will tell how many turns open this is. If you have made such a device please jump in with a design. If no one has made this device and would like a device such as this I am making one and will post some pics of the design once I start it.

    I am always looking to improve my airplane. This would be a big improvement.

    Tony
     
  2. Aug 17, 2013 #2

    Brian Clayton

    Brian Clayton

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    what about a knob with a graduated shaft that screws out or in of its mount as you turn it. Like some pressure regulators? I have seen something made like that, I just cant think exactly what right this minute.... The only thing that comes to mind right this minute is a old algon injector nozzle.
     
  3. Aug 17, 2013 #3

    Pops

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    On the Zenith carb on my 1835 cc, 4 cylinder VW, I just have to turn the mixture screw 1/2 turn between summer and winter. No adjustment from the cockpit needed. Completely trouble free. Dan
     
  4. Aug 17, 2013 #4

    N8053H

    N8053H

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    All last summer and the summer before I did just as Dan stated. Never really missed with the mixture control. I was always fouling spark plugs. I then listened to Mike Bush speak about leaning and every since have been doing as Mike stated. My plugs never looked better. But doing this I am always trying to remember how many turns I keep turning this knob. I never get it right. MY little 1/2 vw notices the weather change and I must lean or rich accordingly.

    I did notice leaning as Mike stated I have been able to get a few more rpm's out of my engine. I saw 3150 on the tach for the first time last evening. I never was able to get her over 3000 rpm's before.
     
  5. Aug 17, 2013 #5
  6. Aug 17, 2013 #6

    kent Ashton

    kent Ashton

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    Never flown behind a 1/2 VW but if you fly it like a Lycoming, the device shouldn't be necessary: Lean aggressively on the ground to keep plugs clean, use full rich for takeoff, climb and power settings above 75%. When less than 75% power or at any altitude above 8000', lean as much as desired. You can't hurt the engine when leaning below 75% power. My carb Lycoming is 8.5:1 compression. I imagine any air-cooled engine with similar CR can use the same guidelines.
     
  7. Aug 17, 2013 #7

    cluttonfred

    cluttonfred

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  8. Aug 17, 2013 #8

    Turd Ferguson

    Turd Ferguson

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    I agree with Dan, mixture control is a waste of time on an airplane that rarely ventures above 3000 ft.

    However, I owned a plane for several yrs with a C-85 continental and stromberg carburetor that didn't have a mixture control. Often flew it at 9500' on cross countries and it performed just fine.
     
  9. Aug 17, 2013 #9

    Vipor_GG

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    Be careful leaning an engine at high power loads. Too lean at high power can burn holes in even forged pistons and can damage aluminum heads. This sucks at the drag strip and could be deadly in the air.
     
  10. Aug 27, 2013 #10

    N8053H

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    Some carbs are altitude compensating not sure about this one you mention but some are. Everyone whom is commenting do you even try to adjust for LOP at cruise or do you just leave it alone?
     
  11. Aug 27, 2013 #11

    Jay Kempf

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    While that is a way to tell where the mixture control handle is positioned it is not a way to tell where you have set the mixture for the conditions and altitude if you have a non-altitude (mass flow) carburetor. There are two ways to measure mixture: in the tail pipe and at the fuel flow side. The fuel flow side only tells you the fuel flow and not the air to fuel mixture. Motorheads with old cars have been using simple tail pipe probes to set mixture for a long time. I have an old hot wire annemometer setup that does this and well for one data point at a time. Others use full spectrum O2 sensors in the tail pipe and a voltmeter to scaled to air to fuel mixture to watch the mixture. This is by far the best way to monitor. Head and exhaust gas temps are also great indicators of overleaning conditions.

    Here's a cheap easy AFM you can install: Amazon.com: Innovate Motorsports 3844 MTX-L Complete All-In-One Air/Fuel Ratio Gauge Kit: Automotive
     
  12. Aug 27, 2013 #12

    Pops

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    If you really want to do it on the cheap. Weld a spark plug bun on your exhaust system, and use a Bosh Oxygen Sensor Part # 0-258-001-027 ( 18 mm thread) and for an indicator, use a Newark Inone Part # 39C2800 LCD Display panel, ( $25.13)

    EMA 1710 - LASCAR - VOLTAGE METER | Newark
     
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  13. Aug 27, 2013 #13

    Dan Thomas

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    An EGT gauge is the way the aviation world sets mixture.

    Dan
     
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  14. Aug 27, 2013 #14

    N8053H

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    I built a 671 supercharged 350 and used something like this. You can see them in this very short video. Its kinda shakey for I had a broken back and could barley walk.

    supercharged s10 - YouTube

    I thought about using egt gauge in this system but not sure where to put the probes or even if I would get good results seeing my tubes are only maybe 10 inches long. Then where would they go within this 10 inches.

    When building this truck I stuck the probes after the collectors. As you will see she runs lean until warm. I had a head crack and that is why one exhaust pipe shows signs of heat. I replaced the heads and sold her for I could no longer work on her. It cracked under one of the valves. It was not real bad but I noticed this pipe and fixed it.

    I set my mixture in flight using my RPM gauge and my Butt. Not very scientific but I am getting good results. Plugs are lasting longer and looking a lot better.

    Tony
     
  15. Aug 28, 2013 #15

    Dan Thomas

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    Four inches below the stack's flange at the exhaust port.

    The problem with a mechanical position indicator is that it makes no allowances for air density changes. The position that's fine today isn't fine next month when it's colder or warmer and it isn't fine at a different altitude than where you found it fine when you set it. Only an EGT will tell you where peak temperature is.

    Dan
     
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  16. Aug 29, 2013 #16

    Topaz

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    +1. That's how I was taught to lean, along with watching the tach. Lean to where you see a slight RPM drop, then richen back up a little, and watch the EGT. Do it with any major altitude change, and maybe once or twice on a long cross-country "just because". I know you can get CHT and EGT probes for VW's. Spruce has them - or at least they used to. Haven't checked in a while.
     
  17. Aug 29, 2013 #17

    Jay Kempf

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    Which would all happen automatically and perfectly accurately if we would all use MAP, MAF and a wide band O2 sensor. Why people want to intervene in combustion I do not know. We aren't that good at it as a species. We were probably better at it when we had to smelt our own axe heads (checking forehead slope right now for any regression).
     
  18. Aug 29, 2013 #18

    Topaz

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    Oh, agreed. For a little "$100 breakfast" airplane, I can't see the justification for that kind of complexity but, for anything much more sophisticated, it's a real shame someone hasn't invested the time and money for a generic system that can be applied to most aircraft motors, with just a software change to account for each kind of powerplant.

    I suspect that, if you took that project to the "maker" community, you'd have a working system inside of six months. You could only apply it to experimentals - getting the STC for each installation variant of certified airplane engine in each kind of certified aircraft would be a nightmare.
     
  19. Aug 29, 2013 #19

    Jay Kempf

    Jay Kempf

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    Did and done. Works with a $39 Ford injector and off the shelf stuff.

    I wouldn't build an engine without fuel injections just for fuel savings.

    A three cylinder Geo engine comes stock with single throttle body fuel injector and MAP and MAF sensors as well as O2. Why would you take that stuff off and put on a carb? And why wouldn't you take all that stuff and put it on whatever engine you are doing.
     
  20. Aug 29, 2013 #20

    Topaz

    Topaz

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    You know me. I have a VW in mind. ;)

    Do you know how high (altitude) automotive fuel-injection maps are programmed for? Or are you talking making a custom map?
     

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