Zenith Carb In-Flight Adjustable Mixture?

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I've been reading about the Thatcher aircraft, and they run Zenith Carbs without mixture controls.

Can mixture controls be added to a Zenith Carb or would that require a different carb?
 

Pops

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Marc W

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I made my mixture control with these items from Ebay: https://www.ebay.com/itm/105-Degree-Angle-1-4-inch-Extension-Hex-Screwdriver-Drill-Bits-Holder-Adapter-US-/192580835257?hash=item2cd6b657b9
and https://www.ebay.com/itm/1-4-Hex-Drill-Bit-Flexible-Screwdriver-Extension-Socket-Holder-Adapter-30cm/392292611785?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l46252

I put a piece of 1/4" aluminum hex shaft on the mixture screw. I made an aluminum collar to attach the angle drive to the carb and the flex drive goes through the firewall. From that, I have a shaft back to where I can reach it to twist the drive. No pictures but I could take some next time I am at the airport. The cowl is off right now since I adjusted the valves today.

It does work good. I do adjust it when we have wide temperature swings like we do this time of year.
 

Pops

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Looks like that would work very good. Thanks.
 

lakeracer69

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Good Idea Marc. Would love to see some pictures when you get the chance. Do you use it as an idle cut off as well to shut the engine down, or just mixture adjustment?
 

Dana

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I had a cockpit adjustable mixture on my Zenith. I think it was the kit Mosler used to sell, with two universal joints. It didn't make much difference; you can't use it as a shutoff, it won't close it down that far, it's just a fine adjustment. Like Pops I mainly just adjusted it in the spring and fall.

Most people don't fly VW planes high enough to need to mess with the mixture in flight.
 

Turd Ferguson

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I've been reading about the Thatcher aircraft, and they run Zenith Carbs without mixture controls.

Can mixture controls be added to a Zenith Carb or would that require a different carb?
I had a Cessna 120 for several yrs. It had a Stromberg carb with a back suction mixture that was safetied to full rich, as most of them are.

Before I owned that plane I didn't think you could do much with a plane that didn't have a mixture control. I was wrong. I flew that plane at 9,500 ft on 600 mi cross country flights with no issues. Not having a mixture control is not a handicap. As Pop's says, if it's not there is is 100% reliable.
 

Pops

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The Zeith carb on a VW is a better carb than a Stromberg carb on a small Cont. Just needs an idle shut off.
 

Marc W

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I took some pictures of my mixture control today. The needle is leaking so the carb needs to come off anyway so it worked out to get pictures of the parts. Anyway, first pic is my cockpit control. The shaft is 1/2" aluminum tube and the handle is a bit crude but it works!
upload_2019-11-1_19-5-58.png

I cannibalized a 1/4" hex drive extension for a socket to connect the shaft to the flex drive. The socket is held in the tube with a set screw. The set screw is partly hidden behind the top of the aluminum tube.
upload_2019-11-1_19-9-48.png

This is the connection to the carb.
upload_2019-11-1_19-13-13.png

One end of the collar that attaches the angle drive to the carb. This end clamps to the angle drive.
upload_2019-11-1_19-15-20.png

The top end of the collar is attached to the carb with three set screws.
upload_2019-11-1_19-16-26.png

Finally the piece of 1/4" hex aluminum that attaches to the mixture screw. The inside hole and the cross hole are drilled oversize in order to avoid any side loading on the mixture screw. The hex is attached to the mixture screw with the original roll pin that I shortened.
upload_2019-11-1_19-21-29.png

It is simple and cheap and works well. There is a little spring in the flex drive when it is rotated to the left but it isn't enough to cause any problems.
 

N8053H

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I use the mixture control to shut my engine down on my Zenith carb. I also use it to run LOP while on the ground. Doing this my plugs always look just like they do when you take them out of the box.
 

Pops

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I use the mixture control to shut my engine down on my Zenith carb. I also use it to run LOP while on the ground. Doing this my plugs always look just like they do when you take them out of the box.

So you lean it out until the engine stops with the cockpit adjustable main mixture screw. Wish the Zenith had a fuel mixture shut off like on a Marvel Schebler Carb.

With mine being not cockpit adjustable, I shut the engine down by turning the fuel valve off then the mag.
 

N8053H

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So you lean it out until the engine stops with the cockpit adjustable main mixture screw. Wish the Zenith had a fuel mixture shut off like on a Marvel Schebler Carb.

With mine being not cockpit adjustable, I shut the engine down by turning the fuel valve off then the mag.
Turning this needle stops the inflow of fuel into the float bowl. It is used to adjust the high speed mixture. At idle it is not really leaning anything. Even though you set this needle before adjusting the low speed side of this carb. You adjust the high speed side first then the low speed side. All you are doing when closing this needle is shutting of the fuel supply to the carb. It takes a few mins for the float bowl to run dry then for the engine to quit. Shutting of the fuel valve does the same thing. I always let the engine run out of fuel and die before shutting off the mag. I reference this to unloading a gun. I don't like leaving my engine sitting with fuel in the carb for this leaves the engine loaded or ready to run. The way I do it, even if the mag is left on the engine will not start. If someone comes along and turns the prop the engine will never start. I don't leave my engine loaded. I unload it before putting the plane away.
 

Pops

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I agree, I prefer to unload the gun. So for a restart you turn the cockpit adjustment out the same amount you turned it in. One time my neighbor was in his hanger and walked by the prop of his C-172 and happen to bump the prop and the engine started and he was up against the inside of the hanger door with both hands holding against the tip of the spinner while it was running trying to keep the airplane from moving forward, hollering for help.
 
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