Jet Flow Rate Testing Rig..

[Kevin in NJ]

Many moon ago I started building a carb jet flow rate tester.

I had some chunks of thin copper tubing and some attachments. I found a tube chime from a cheap grandfather clock in the trash. I liked the nice sharp edge at the one end so I knew I could be real exact on the length. PVC pipe did not seem a nice an edge to me.

Back then I set it up for a 36" column and never really used it.

So recently I dug it out. Set it up for the 37.25" Ford spec and printed out the stuff from Vince's website.

So as you can see in the picture it is not pretty like Tom makes stuff. The cup on top is one of the old sippy cups from my sons with some silicon glue to catch the overage. I jambed a fitting I had laying around and I had some clear tubing that just fit in the hole so it drains back down to the bucket. The wire hangar on the top was bent to one side to make the tube level because of the weight of stuff below. The pump is borrowed (with permission) from my neighbors fish pond. It has a hose the kind of fits in the hole and is wrapped with electrical tape to hold it in place and keep the water from spraying.

I have some regular 3/8" copper tubing at the 37.25" point. The ID is a bit big for the 5mm threads of the jets. I managed to get some solder in the pipe and tapped it the common 5mm X .80. The correct thread is 5 X .75, but good luck getting that one. In fact on the of cheapo china ones is advertised as 5 x .75, but they send a .80- so watch out. As it turns out the .80 is close enough and it is real soft anyway so it works fine for this.

So at this point I have done 3 different types of original jets. The NOS looking jet came in perfect the first time. The other 2 needed some cleaning. By cleaning I mean a bare wire about the right diameter just rubbed some. This usually cleans off the hard stuff with out changing the diameter. The 2 were off by around 5 ml low. When I cleaned and tried again they were mid range Ford specs.

I have to add that I do not have the correct size measuring cylinder. I have one that goes to 150ml and it goes by 10ml increments. I have ordered a 250ml by 1ml cylinder. When that one arrives I can look closer at the accuracy of my set up. Then I will work the 50 or so jets I have laying around.

[MikeK]

You do not necessarily need a graduated cylinder. Since 1g of water = 1 ml you could use a gram scale. Just weigh the empty container first. Arguably more accurate than an inexpensive uncalibrated and uncompensated graduated cyl measurement.

[Kevin in NJ]

Originally Posted by MikeK

You do not necessarily need a graduated cylinder. Since 1g of water = 1 ml you could use a gram scale. Just weigh the empty container first. Arguably more accurate than an inexpensive uncalibrated and uncompensated graduated cyl measurement.

You know I did not think of that...

So I tried it with my Harbor Freight cheapo small scale that is a bit beat up.
It kept coming out lower then I thought it should. So I used by 20ml and put in 2ml of water and it weighed 1.6 grams. Guess that scale is not so good

[MikeK]

Originally Posted by Kevin in NJ

You know I did not think of that...

So I tried it with my Harbor Freight cheapo small scale that is a bit beat up.
It kept coming out lower then I thought it should. So I used by 20ml and put in 2ml of water and it weighed 1.6 grams. Guess that scale is not so good

More likely a reading error on the meniscus. Try filling it to 20ml and weigh it. That will reduce the visual meniscus error effect by a factor of ten from the 2ml trial. If your scale is fair you should read between 19 and 21. If not the scale may have spent too much time at the bottom of the 'Harbor'.

[BILL WILLIAMSON]

Since Rube Goldberg isn't here to help me, I'll just BUY some flow tested jets from Renners' Corner.
Bill Simple

[Jon]

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Mike makes a very good point. If you use a larger volume and then divide you will get a far better reading. The starting, stopping, and timing can all induce errors.

[Kevin in NJ]

Originally Posted by Jon

Mike makes a very good point. If you use a larger volume and then divide you will get a far better reading. The starting, stopping, and timing can all induce errors.

Keep in mind it is a minute of collecting.

The start and stop errors are way in the weeds.

I consider all these items when I approach these tests. Something about being a scientist for my real job has be ask a lot of questions.

My first concern was to consider the repeatability of measurement. I was getting a fractional difference in volume which I attribute to collection in a bigger container then pouring off to a smaller container to measure. Then I worry about left over water in the container and so on.
I did a bit of measuring and realized my measuring was not repeatable with enough accuracy for what I thought I should see. So I spent $6 for a proper sized measuring tube.
Once I get that I will see how accurate I can repeat measurements and wind that up into my error equation.