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Old 03-06-2017, 05:24 PM   #1
Jim M
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Default Bench test Carb?

My 29 Roadster has been leaking fuel if I forget to shut off the gas when parking for the day. Rebuilt the carb just about 2 years ago but has not had a lot of use. Hooked up the float tester and don't know if it was an accurate reading but the gas was WAY over where it should be so I took the carb off and went to the bench and spent a lot of time cleaning, specially the surfaces where the bottom joins the top and where it mounts to the manifold. Trying to hook up the float tester while the carb is on the car is a PIA. Is there a suggested way to bench test it BEFORE mounting on the manifold (and get accurate test results)? Any suggestions will be appreciated. Thanks, Jim
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Old 03-06-2017, 08:57 PM   #2
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Default Re: Bench test Carb?

I obtained a plastic gas tank from an old lawn mower and added a plastic shut off valve and the correct fitting on the outlet so it would connect to the carburetor.


I then took a piece of angle iron drilled it so I could mount the carburetor, and I drilled a hole between the mounting holes so I could look in the throat area.


Put the angle iron in a vice, level it, bolt the carburetor on, and put a pan under the carburetor for spill collection.

Hook up the gas line, hang the lawn mower tank at the approximate level of a model a tank and test away.
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Old 03-06-2017, 09:09 PM   #3
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Default Re: Bench test Carb?

Based on what I've read here on the barn and my own experience, I think most if not all carbs will leak if the fuel is not shut off at the tank when parked.....

I let mine idle with the fuel shut off to empty the carb bowl when parking for extended periods of time...like overnight...
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Old 03-06-2017, 09:41 PM   #4
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Default Re: Bench test Carb?

Quote:
Originally Posted by Jim M View Post
My 29 Roadster has been leaking fuel if I forget to shut off the gas when parking for the day. Rebuilt the carb just about 2 years ago but has not had a lot of use. Hooked up the float tester and don't know if it was an accurate reading but the gas was WAY over where it should be so I took the carb off and went to the bench and spent a lot of time cleaning, specially the surfaces where the bottom joins the top and where it mounts to the manifold. Trying to hook up the float tester while the carb is on the car is a PIA. Is there a suggested way to bench test it BEFORE mounting on the manifold (and get accurate test results)? Any suggestions will be appreciated. Thanks, Jim
You may have a messed up input valve(I don't know the real name for it but it is the one the float pushes up to shut off the gas). If it sticks open you can tap the carb and if the gas stops, then it could be this valve. Then replace it.
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Old 03-06-2017, 10:35 PM   #5
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Default Re: Bench test Carb?

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Originally Posted by 1955cj5 View Post
Based on what I've read here on the barn and my own experience, I think most if not all carbs will leak if the fuel is not shut off at the tank when parked.....

NO, only carbs that are not properly restored leak.

If your carb leaks, for your safety please fix it properly.

I had a local guy once tell me a constant stream out of the carb on his truck was just the truck's personality. I offered to help fix it and he did not feel it needed to be fixed.
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Old 03-06-2017, 10:56 PM   #6
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Default Re: Bench test Carb?

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"if the fuel is not shut off at the tank when parked"
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Old 03-07-2017, 01:24 AM   #7
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Default Re: Bench test Carb?

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Originally Posted by Kevin in NJ View Post
NO, only carbs that are not properly restored leak.

If your carb leaks, for your safety please fix it properly.

I had a local guy once tell me a constant stream out of the carb on his truck was just the truck's personality. I offered to help fix it and he did not feel it needed to be fixed.
Doesn't need to be fixed now,
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Old 03-07-2017, 12:35 PM   #8
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Default Re: Bench test Carb?

Of course I understand the need to repair an obvious fuel leak.

Somewhere I have a picture of a nice looking Willys wagon suffering the same fate as in Mike's picture..

Jim's first comment was that the roadster leaks if he forgets to shut the fuel off at the tank when parking for a day. He didn't say if it left a puddle or if it was just damp from fuel.

Now I was taught somewhere along the way to always shut the fuel off at the tank when parking the Model A...same with the old tractors and hay equipment that used gravity fed fuel systems.

When parking overnight or longer I also let the Model A run with the fuel valve off until it dies of fuel starvation. I've read here on the barn that this is a fairly common practice.

Isn't this done to prevent a full carb fuel bowl from seeping either through the vents or jets due to thermal expansion or due to a small amount of fuel getting by the float valve if the supply/tank valve is left open?

I know when I first brought the truck home the tank valve would allow a small amount of fuel to pass when in the closed position. In the morning the carb would be damp from fuel even though it was dry when parked. A replacement fuel valve fixed this problem.
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Old 03-07-2017, 03:52 PM   #9
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Default Re: Bench test Carb?

Several good reasons for shutdown procedure of main gas shutoff and run carb dry. Not to say the float valve shouldn't be able to seat properly and not weep. Your car, you can do what suits you. Takes some knowledge, and some experience fixing the carb correctly. That is a good reason the rebuilders need to charge enough to pay for their work, and their experience. Flea market buyers have convinced me that most people don't expect a simple zenith to be a challenge to repair/restore. and therefore, shudder at my valuation.
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Old 03-07-2017, 07:37 PM   #10
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Default Re: Bench test Carb?

Thanks for all the good ideas and comments. I try to remember to shut the valve off and let the car run to use up the reaming gas but at 73 doesn't always happen. That being said I am going to put a new float valve in and take the suggestion of putting 2 washers on it. The carb was leaking more that just getting damp - there was a small spot on the floor when I forgot to shut it off. Not good and definitely potentially very dangerous. I will post the results when I get finished. Jim
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Old 03-08-2017, 07:38 AM   #11
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Nice graphics Mike!

they look SOOOOOOOOOO real!
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Old 03-08-2017, 08:30 AM   #12
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Default Re: Bench test Carb?

Quote:
Originally Posted by Jim M View Post
My 29 Roadster has been leaking fuel

<snip>

Trying to hook up the float tester while the carb is on the car is a PIA. Is there a suggested way to bench test it BEFORE mounting on the manifold (and get accurate test results)? Any suggestions will be appreciated. Thanks, Jim
Jim-
There is a simple procedure for adjusting the carburetor float height on the bench, as you asked for, that is more commonly used than the fuel level gauge. It is called the "Dry Float Height" adjustment.

You take the top half of the carburetor in your hand, with the float valve, gasket(s) and float installed, and hold it upside down from how it is mounted on the car. Gravity makes the float close the float valve, just like fuel in the bowl will do when it's in the car.

As you hold the carb top in one hand, you measure with a ruler the distance between the machined carb gasket surface (no gasket!) and the soldered seam of the float. You want it to be 1 inch. You usually need to have more than one fiber washer in there, under the valve, to get enough height (unless someone has modified the float).

I wish I had a picture of this, but I don't. I looked online for one and could not find a good one.

Some vendors sell thick and thin versions of these fiber gasket washers, so you can mix and match the washers used to get closer to your target 1". I have also taken a thick fiber washer, when that's all I had, and rubbed it with my finger across some 400 grit sandpaper on my workbench to make it thinner. You can sand a bit, then test fit and measure, sand a bit more and measure. Pretty soon you're at 1".

It is better to err slightly on the "over 1 inch side" than it is to be "under 1 inch", because under 1" here means you get a higher fuel level, which is more prone to drip.

Do not bend the float to get this 1" Dry Float Height. Add gaskets.

You can confirm that this Dry Float Height gives you your target fuel height in the bowl later, when the carb is installed. Unless you messed something up, it will be.

I hope this helps. If you have any questions, let me know.
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Old 03-08-2017, 08:08 PM   #13
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Default Re: Bench test Carb?

Jim,

Thank you soooo much for your response. That is exactly what I was looking for. I have ordered the new style float valve and will put it in when I get it. I have the washer from the existing valve so I will try it first with one washer then two if needed. Seems like most of the posts indicate it is needed. I will make sure I will err slightly over the 1" . I hope to get everything I need by weekend and put the carb back on on Monday and give it a test. I will make sure to report my results. Thanks again to everyone for their help!

Jim
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Old 03-08-2017, 08:26 PM   #14
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Default Re: Bench test Carb?

Jim's response was right on the money... FYI brattons carrys different thickness gaskets in this .95 kit
https://www.brattons.com/zeinth-floa...-shim-kit.html
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Old 03-08-2017, 08:52 PM   #15
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Default Re: Bench test Carb?

Would Jim's method of measuring work for the Marvel carb as well? Meaning 1", etc?
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Old 03-08-2017, 08:58 PM   #16
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Would Jim's method of measuring work for the Marvel carb as well? Meaning 1", etc?
Better yet here is a nice marvel thread
http://www.fordbarn.com/forum/showth...ght=dissection
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Old 03-08-2017, 09:32 PM   #17
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Default Re: Bench test Carb?

[QUOTE=Jim/TX/GA;1439698]Jim-...................................I wish I had a picture of this, but I don't. I looked online for one and could not find a good one....................../QUOTE]


Jim's recommendation is 1" to the soldered seam.

Here is a page from the Model A Ford Carburetors by Paul Moller.
Paul's setting is 5/8" to the top of the float.
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File Type: jpg Scan0040.jpg (27.4 KB, 14 views)
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Last edited by 160B; 03-08-2017 at 09:47 PM. Reason: added cover photo
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Old 03-08-2017, 09:38 PM   #18
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Default Re: Bench test Carb?

Quote:
Originally Posted by Mitch//pa View Post
Better yet here is a nice marvel thread
http://www.fordbarn.com/forum/showth...ght=dissection
That is a very detailed thread, thanks!
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Old 03-09-2017, 12:26 AM   #19
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Default Re: Bench test Carb?

Had issues with a couple of Marvel's with throat leaks. The solution that has worked so far is to find a viton tip original style valve for the float valve set up and to check for no pinholes in brass float. The float was adjusted to sit about 1/32" higher than the carb body mating surface dimension for added insurance as in the prior post photos. The grose jet type ball valve was found not to seat well but that could have been unique to my carbs.
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Old 03-09-2017, 02:28 PM   #20
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Default Re: Bench test Carb?

One item that is overlooked is removing the wear spot on the float bracket where float valve rides. If this wear spot is not removed it will affect the travel of the float and thus the float valve will not fully seat, thus causing a leaking carburetor.

If you take very fine sand paper 400 and sand on the float bracket where the float valve rides this wear spot will be easier to detect.
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