How to: Jet flow test?
 

Hi,
I have bought myself a Zenith Carb rebuilt set from Snyders and plan on testing the jets with the 36 inch water column. I have some difficulties finding accurate information on how to properly setup the test. My question is:

I have some small diameter silicone hose which perfectly can be squeezed onto the jets obtaining an automatic water tight seal. I guess the unstretched inner diam. of the hose/tube is 5mm which is a little less than 1/4 inches. I can extend the hose 36 inches upwards and plug it into a large bucket or container which I could fill with water still observing that the top water level in the bucket stays at 36 inches. However, I do know that a small diameter tube restricts flow due to internal resistance, so is my tube too narrow? And is there a minimum diameter?

Lucas

Re: How to: Jet flow test?
 

The flow won't be restricted by that diameter but with the set up you describe you may have a problem measuring the flow out of the jet whilst at the same time keeping the height of water at 36 inches . Do a search on this forum eg http://www.fordbarn.com/forum/showth...w+testing+jets and you should get some ideas. I made a rig from copper tubing off cuts and some plumbing left overs I simply connect it to the water tap rather than having a pump recirculating the water as some of the rigs are. If you get stuck email or let me know and I'll send you some pictures. Give my love to Denmark. John B

Re: How to: Jet flow test?
 

Yep, I used to do that for newer cars back in the 70's, including my 1962 Chevy 283 with stick and overdrive. Still couldn't get the mileage above 18 MPG.

Re: How to: Jet flow test?
 

That's no way to do it. You need a solid tube to serve as the vertical column of water, e.g., a piece of copper plumbing tube or PVC, and allow the water to spill over the top with the top open while the water is fed into the tube from the bottom by way of a hose attached to a faucet, your kitchen or shop sink for example. You need a piece for the column about 40 inches long with an O.D. of about 7/8". This extra length is needed so you can attach a cap or inlet at the bottom of the column tube for the water to enter and then up on the side 36 inches from the top to attach a tube which will be the attachment point for the jets under test. Attach a small 1/4 inch O.D. tube in the side at that point for that purpose. If you use copper then you can soft solder the parts together.

A piece of Tygon plastic tube 3/8 inch O.D. is used to connect the main, cap or compensation jet to the stand. A small 1/4 inch O.D. piece of Tygon inside the 3/8 inch O.D. tube will hold the idle jet. Connect the other end of the 3/8 Tygon to the 1/4 O.D. tube referenced above on the side of the column.

At the top of the column tube you can rig up a wire hook or something by which to hang the tube in a vertical position over the sink so the water can spill over the top and fall into the sink instead of on the floor. The jet being tested is installed in the 3/8 O.D. Tygon tubing and the water is turned on. When the vertical column tube is full of water and it spills over the top, the faucet is adjusted so that the spill-over is minimized. There should be a fine stream of water coming from the jet being tested. Catch the water in a flask or container, marked in cc's or ml's, for a 60 second period. The results will be your cc's per minute per jet. One cc or cubic centimeter is the same as one milliliter or ml.

According to Larry Brumfield and his work, he prefers the following flow rates which I have had good results with:

Main jet = 159 to 163 cc/min
Cap jet = 176 to 180 cc/min
Comp jet = 152 to 156 cc/min
Idle jet = 46 to 50 cc/min

Readings greater than these ranges mean that the fuel flow will be too rich. Lower readings mean the fuel flow will be too lean. And of course you will have to adjust if necessary by lightly reaming the jet if it's too small or soldering up the end and then drill/ream if the jet is too large.

Re: How to: Jet flow test?
 

The carburettor that was on one of my cars when I got it had 3 or 4 pieces of copper wire through the main jet and bent over top and bottom so they didn't come out. The wire had been stripped from an piece of ordinary electrical wire. The car ran VERY well and returned good fuel economy and did so for many thousands of miles till I put a down draft on it. Has anybody come across this method of adjusting fuel flow?
I would rather have a jet of the correct size but one only ever hears stories of repro jets being close but not quite right. I am not familiar with the 36" tests spoken about above. Where do I find all the nitty gritty details?

Re: How to: Jet flow test?
 

I think Edmondclinton has just answered my question. Thanks. Now I can set the flow rates with confidence and hopefully, good results. (maybe by putting strands of wire in the jets that are too large!!!)
I hve been told by a well experienced motor mechanic who specialises in older cars that soldering up a jet and redrilling it is only a temporary fix because the fuel gradually dissolves the lead out of the solder. Has anybody heard of this? If it is so, then the person who put the strands of copper wire in my jets must have really known what he was doing.

Re: How to: Jet flow test?
 

Here is the setup that I use. It does not have to have flowing water. I fill up the milk carton the to appropriate level before each test. I test for 1 minute. Because the milk carton has a large cross section at the height of the water level the drop after each test is a fraction of an inch and does not cause a problem. The rubber tubing I use has an inside diameter many times larger than the jets so it works fine.

Bob


http://www.modelahouse.com/images/flowtest01.jpg

Re: How to: Jet flow test?
 

I have found that a soft solder repaired main jet, for example, flowed exactly the same after 4 years of use as when it was first repaired.

Re: How to: Jet flow test?
 

One for false. Any more?

Re: How to: Jet flow test?
 

Yes, many variations are possible.

Nobody said that the water had to be flowing but my method always ensures that there is an accurate constant 36 inches head of water pressure that does not waver or drop. Based on my research of the Zenith carburetor plant and their methods, I feel that my rig will give test data every bit as accurate as the original factory method. But as with everything, to each his own. Thanks.

Re: How to: Jet flow test?
 

If one was concerned one could use lead-free solder.

Re: How to: Jet flow test?
 

Re: How to: Jet flow test?
 

Here's how Zenith did it

http://www.zenithfuelsystems.com/doc...istory2009.pdf

Re: How to: Jet flow test?
 

Mike there is no bottom, I cut it off. No problem with air pressure.

Re: How to: Jet flow test?
 

Hi bikemaniac, do a google search for PERFORMANCE TUNING OF THE MODEL A ZENITH CARBURETOR and download the document. I'm sure you will find it most helpful.
Runner

Re: How to: Jet flow test?
 

here is the set up I have, it has a submersible pump in the pail feeding the bottom of the column. The centerline to centerline distance from the overflow to the test port is 36 inches

http://www.fordbarn.com/forum/pictur...ictureid=17466

http://www.fordbarn.com/forum/pictur...ictureid=17465

Re: How to: Jet flow test?
 

Here is another approach. The inlet is fastened to an external water outlet and the valve is set to just barely let the overflow drip slightly, (like in the first photo) maintaining a constant head pressure.

Attachment 209450

Attachment 209451

Attachment 209452

Re: How to: Jet flow test?
 

Your method is basically the same as mine except I use the kitchen faucet to feed the bottom of the tube. The distance from the end of the tube opening to the test port is 36 inches on mine as well.

Re: How to: Jet flow test?
 

Mine operates basically the same way in that the faucet is adjusted to allow only enough water to dribble over the top of the tube while at the same time a steady stream of water is emerging from the jet being tested.

Re: How to: Jet flow test?
 

There is a technical article that may be of help. Go to the web site of the Santa Anita A's of Arcadia, California at santaanitaas.org. On the home page put your cursor on "Technical Reference". My name will appear below, click on it, and it will bring up a menu of articles. Scroll to "Model A Ford Zenith Carburetor Restoration Tips". This is a long how-to pdf file article with many photos. there are several showing a flow tester in use. You are welcome to download the article and print it out.

Tom Endy