Ford GAV carb adjustment

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Posts: 12
Joined: Sat May 27, 2017 2:36 pm

Ford GAV carb adjustment

Post by donbrewer »

I hope anyone with a Ford Model A or B can help me with this question. Does anyone have a connection to the GAV that will provide mixture control? Every a/c and photo I have seen, the GAV is wired in a fixed position or there is no control attachment at all. If this valve is ignored ,then there is no way to control mixture with an increase [or decrease] in altitude. Is the GAV set to about 1/4 to 1/2 turn open and then the resulting mixture then accepted? I know it will be a difficult cable attachment as the valve is reversed in position due to the engine being reversed. Please give me any info that you have.

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Re: Ford GAV carb adjustment

Post by taildrags »

Don; I had a similar question in my mind when trying to find out how KR2 builders with VW engines had made the mixture on the Zenith carb cockpit adjustable since the adjustment on those carbs is a tee-screw sticking out the bottom rear of the carb. The KR can easily leave an airfield at sea level and quickly be up at 12-15,000 ft for cruise, so mixture control is a must. For Piet pilots, a climb from field elevation to cruise may only be 2-3,000 ft of altitude change and mixture adjustment would not normally be a factor if the mixture was already adjusted for the departure field elevation. If you feel that you will be operating widely enough that you expect to operate out of fields and at altitudes that vary significantly enough to be a concern, then mixture control would be important so your engine can smoothly develop full power when needed.

With the Zenith on the VW, the adjustment range between sea level and high altitude cruise needed to be more than just 3/4 to 1 turn as it may only need to be on the Ford A or B carbs with GAV, so what was used was a vernier-style knob (not in-out but just rotational) with friction adjustment that allowed fine adjustment but would still hold position without vibrating off the setting. Basically just a Bowden cable with the outer sheath fixed and the inner wire connected to the mixture control screw so that it can be twisted in either direction to adjust the mixture. A gentle loop in the Bowden cable will let you make the 180 change in direction back towards the cockpit if the GAV faces forward on your setup.

If you don't expect to be flying between greatly varying altitudes, then I would think that the mixture should just be set for clean, tan spark plugs in the usual way and the GAV left there. Disclaimer: I do not fly a Ford on my airplane.

Brian Amato
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Joined: Fri Aug 31, 2018 9:23 am

Re: Ford GAV carb adjustment

Post by Brian Amato »

I'm not nearly that far on my Piet but it will have a Model A engine in it. I'm big into Model A cars....I drive a newly restored 1931 Tudor Sedan and President of the local Model A Club. I run my GAV at about 3/4 of a turn out for almost all my driving.
I wouldn't think it would be that hard to rig the same kind of rod from inside the cockpit out to the Model A carb, would it?
Traverse City, Michigan

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