Inside the Venturi

AA Ford Discussion Group relating to the repair and restoration of your AA Ford.
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captain marty
Posts: 208
Joined: May 13th, 2009, 6:58 pm
Body Type: firetruck
Model Year: 1928
Location: Tulsa

Inside the Venturi

Post by captain marty »

The venture in the carb I’m working on refuses to budge and I do not want to destroy the upper body. I’ve decided to leave it in place and use it. Question: How smooth does the inside of the venture be?
Captain Marty
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Brady
Posts: 361
Joined: October 21st, 2003, 1:38 pm
Body Type: None
Model Year: 1930
Location: Norwich, NY 13815

Re: Inside the Venturi

Post by Brady »

Marty: Just buff it good to smooth and clean, and not so much that the angle or dimension changes at the smaller inside diameter. You can feather it out at the very top and not change the dynamic of the venturi effect. The biggest thing to concentrate on is how clean and clear the passages are. If you have some books, there will be methods to open, clean, and re-plug the passage ends. Have fun, and don't worry too much - they're pretty forgiving as long as the cast iron isn't damaged. I've heard that the 'govt-gasahaul' can ruin the vitron tip of some float valves. Keep reading and enjoy the work.
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captain marty
Posts: 208
Joined: May 13th, 2009, 6:58 pm
Body Type: firetruck
Model Year: 1928
Location: Tulsa

Re: Inside the Venturi

Post by captain marty »

Thanks Brady
I have it pretty smooth inside but can not be certain the small ID is exactly where it was. I bet it's going to work fine.
Marty
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Brian T
Posts: 400
Joined: December 27th, 2008, 9:57 am
Body Type: 82A
Model Year: 1929
Location: San Diego

Re: Inside the Venturi

Post by Brian T »

Marty,
If you leave the venturi in place you will find the bowl gasket will not fit, if you have to destroy it to remove it, they are reasonably cheap to buy.
Nothing can be made fool proof, fools are ingenious bastards.
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Brady
Posts: 361
Joined: October 21st, 2003, 1:38 pm
Body Type: None
Model Year: 1930
Location: Norwich, NY 13815

Re: Inside the Venturi

Post by Brady »

Thanks Brian: That's right, and I wasn't thinking that far ahead for a "good" rebuild. I have in the past jut cut and worked it around on the underside of the top half, but that was for a "doodlebug grade" operation. I guess Marty should go ahead and use that venturi puller tool and get the old one out, broken or not - I'm sure he would feel much more comfortable after having put a lot of work into getting his carb back in shape. Thank you for posting. FB
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captain marty
Posts: 208
Joined: May 13th, 2009, 6:58 pm
Body Type: firetruck
Model Year: 1928
Location: Tulsa

Re: Inside the Venturi

Post by captain marty »

My venturi is stuck in the top piece and is seated well. It comes together well with gasket so I don't see a problem there.
I did receive my "Zenith Model A Carburetor Restoration Guidelines" book written by Mr. Steve Pargeter, which goes into so much good detail. I recomend this book to anyone rebuilding a carb.
Marty
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TruckMan
Posts: 132
Joined: March 10th, 2009, 10:36 am
Body Type: Garwood Dump
Model Year: 1928
Location: Wisconsin

Re: Inside the Venturi

Post by TruckMan »

For fuel in my AA, I use premium without ethenol. Sure it costs more but this is not my daily driver, so it costs peanuts over the course of time. I do the same for my lawn mower and snow blower. It is worth it for trouble free operation.
TruckMan
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1crosscut
Posts: 877
Joined: December 25th, 2010, 7:22 pm
Body Type: 82-A
Model Year: 1929
Location: Lincoln, NE

Re: Inside the Venturi

Post by 1crosscut »

TruckMan wrote:For fuel in my AA, I use premium without ethenol. Sure it costs more but this is not my daily driver, so it costs peanuts over the course of time. I do the same for my lawn mower and snow blower. It is worth it for trouble free operation.

I agree with not using ethanol if at all possible. Here in Nebraska ethanol free fuel has been easy to come by. Now that is going to change though.

I personally avoid using premium as it give less mileage and performance.
The only reason to use premium is if you have a high compression engine that is prone to knocking due to pre-ignition. Premium fuel is actually harder for your engine to burn. The higher the octain number the harder it is to ignite the fuel.
Dave
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Dave
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captain marty
Posts: 208
Joined: May 13th, 2009, 6:58 pm
Body Type: firetruck
Model Year: 1928
Location: Tulsa

Re: Inside the Venturi

Post by captain marty »

I used to use hi test until I was told about regular burning better and that these trucks were built and ran on gas that not all that good in terms of today. I always add a little Marvels Mystery Oil
Marty
Bladehorse
Posts: 112
Joined: November 9th, 2009, 9:22 pm
Body Type: 185-A
Model Year: 1930

Re: Inside the Venturi

Post by Bladehorse »

I have had luck taking a piece of 1/4" rod ,slitting it lengthwise from the end and slipping a piece of emery thru it. Into the drill it goes, and insta flapwheel. Does a good job of polishing insides, and unlike the purchased flapwheels, does not remove a ton of metal. That being said, if you want to remove the venturi, you can always melt it out, as potmetal melts about 1000* below cast iron. Try soaking it in phosphoric acid to dissolve the oxydation between the 2 pieces. this helps allot too. And like you say,, Why remove if it doesnt have to come out?
Bladehorse
Posts: 112
Joined: November 9th, 2009, 9:22 pm
Body Type: 185-A
Model Year: 1930

Re: Inside the Venturi

Post by Bladehorse »

Oh and as far as fuel goes, for a long time I was buying paint thinner at home despot for 1$/gallon when gas was 3$/ mixing to a little less than 1/2 a tank. Was a little stubborn to start, but lotsa torque. Sadly all the thinners are more than gas now :x

Oh an interesting sidebar to venturis. Apperantly they dont need to be there! We only run zeniths, tho we have 3 tillotsen also. I went thru a carb on one at work, and had a odd hesitation problem, unless the mainjet was open a turn. I found all the jets in the carb loose, so i thought this was just the new way of running. It accelerated great, and idled perfectly.I found a week later when I found 2 venturis on the bench when there was only 1 carb. I installed the venturi, then backed off the mainjet to closed. Then found the idle completely unstable no matter how I adjusted things.
Go figure. It accelerated much better, and runs better than the tillotsen it replaced as a temp carb (Even without the venturi!)
Seems the tillotsen had a real hard time of vaporizing the fuel. it took about 1-2 mins to warm up every time it was started so the car could move. And the whole time surging the throttle to keep from dying.
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