Flowing Jets

Marshall57

Marshall57

Senior Member
I have rebuilt a few carburetors and have been having a problem that might be solved with a little extra brain power applied.

I have sealed up all the air leaks I think existed and cleaned the passages, but they all seem to be a little rich at idle. Changing jets from other carburetors or from ones purchased from parts houses seem to have the same result. I did have the manifold faced and it is new and square with the block.

It will run when cold at 1/4 turn out on the choke rod adjustment, but after it warms up anything less than all the way down and tight makes it too rich.

I live at about a mile above sea level and because of this I am wondering if the reason that I can't get a perfect idle is that between standard jets and thin air I am getting a rich idle.

The car has a new engine (now with 3000 miles) and when I went to get it, the thing was purring like a kitten, but it has never been able to idle quite as well for me. I have rebuilt the distributor and I'm pretty sure the problem isn't coming from that end of the equation. It does idle with no problems, and doesn't die when stopping or leak or anything like that, it just sounds fat and somehow less smooth than I know it should.

I have seen and read as much as I can but still don't have a nuts and bolts handle on flowing jets. I would like to try and restrict one or two and try it to see if that would make the difference I'm looking for.

The problems I see is that if you solder up the jet and resize it to the size you are after, it seems to me the solder mess inside the jet would or could do crazy things to the fuel flow.

Any Ideas and/or pictures of rigs set up to flow these jets would be very helpful and appreciated.

I am at the beginning of this adventure and don't want to waste any time and effort rediscovering or reinventing the wheel. Covering ground someone took the time to research and discover is what I would like to avoid.

Thanks for your insights.

 
Last edited:
I've had my share of carb rebuilds (from Whizzers to DC-6) and theory classes too. I agree with you that the high altitude will cause a richer mixture. I must believe that Ford (or after-market) offered smaller jets for your situation. I don't know where to find them though...sorry.
 
Lowering the float level a little will make it run leaner. Not a jet solution, but food for thought...
 
Google "Renners Corner" he sells flowed jets. Give him a call and he can probably fix you
up.
 
When I got my Phaeton, the PO had reduced the size of the jets by stripping the insulation from a piece of ordinary electrical wire. He had 3 pieces in the main jet with the ends bent over so they stayed there. I made the mistake of taking them out and it never ran as well again on a Zenith. The old guy knew what he was doing!
A little trial and error will get it right. The less of the latter, the better.:D
 
ItsA31 said:
Lowering the float level a little will make it run leaner. ......
Click to expand...
not the idle it wont. And it would make a barely perceptable change if any at all ( (unless reaaaalyy low) on main and cap jets .
Build yourself a flow tester as shown in several books, it's certainly not rocket science... even I can do it :D
 
Marshall57 said:
I have rebuilt a few carburetors and have been having a problem that might be solved with a little extra brain power applied

I have sealed up all the air leaks I think existed and cleaned the passages, but they all seem to be a little rich at idle. Changing jets from other carburetors or from ones purchased from parts houses seem to have the same result. I did have the manifold faced and it is new and square with the block.

It will run when cold at 1/4 turn out on the choke rod adjustment, but after it warms up anything less than all the way down and tight makes it too rich.

I live at about a mile above sea level and because of this I am wondering if the reason that I can't get a perfect idle is that between standard jets and thin air I am getting a rich idle.

The car has a new engine (now with 3000 miles) and when I went to get it, the thing was purring like a kitten, but it has never been able to idle quite as well for me. I have rebuilt the distributor and I'm pretty sure the problem isn't coming from that end of the equation. It does idle with no problems, and doesn't die when stopping or leak or anything like that, it just sounds fat and somehow less smooth than I know it should.

I have seen and read as much as I can but still don't have a nuts and bolts handle on flowing jets. I would like to try and restrict one or two and try it to see if that would make the difference I'm looking for.

The problems I see is that if you solder up the jet and resize it to the size you are after, it seems to me the solder mess inside the jet would or could do crazy things to the fuel flow.

Any Ideas and/or pictures of rigs set up to flow these jets would be very helpful and appreciated.

I am at the beginning of this adventure and don't want to waste any time and effort rediscovering or reinventing the wheel. Covering ground someone took the time to research and discover is what I would like to avoid.

Thanks for your insights.
Click to expand...

Lots of jet size info on my web site.

Model A Ford Garage ~ Carburetor Jet Sizes & Flow Rates
www.fordgarage.com/pages/jetflowrates.htm

.
 
Last edited:
Synchro909 said:
When I got my Phaeton, the PO had reduced the size of the jets by stripping the insulation from a piece of ordinary electrical wire. He had 3 pieces in the main jet with the ends bent over so they stayed there. I made the mistake of taking them out and it never ran as well again on a Zenith. The old guy knew what he was doing!
A little trial and error will get it right. The less of the latter, the better.:D
Click to expand...

I did the same thing in the 70's on my 62 Chevy 283 with overdrive, but still never could top 18 MPG. I also did it to a few customer cars to lean them out a bit.

The car has a new engine (now with 3000 miles) and when I went to get it, the thing was purring like a kitten, but it has never been able to idle quite as well for me.

Are you using the same carb now that was on it when it was purring like a kitten?
 
Here are the photos of my flow test stand.

It is made of 3/4” PVC with a column height of 36 inches from centerline of the test port connection to the centerline of the overflow at the top of the column.

It has a submersible pump and a valve downstream of the pump so you can throttle the flow to just get overflow at the centerline of the overflow at the top of the column.

Using the column in a bucket with a pump I have found to be more convenient than using a constant flow from a hose or other source.

picture.php


picture.php



When you solder you will affect the flow characteristics of the jet, and to get the correct flow the jet may need to a little oversize from the original. See photos of original and soldered jets below.

picture.php


picture.php
 
On Vince's web site for jet sizes it only shows the main jet being different for high altitude, as you are having idle problems your engine maybe idling to fast, the GAV should have no affect at idle, get the idle down to 400 or close and adjust air screw for best idle, this should work providing there is no leakage at the throttle shaft.
 
When I did my jets, after soldering the end shut I used a drill bit on the inside of the jet, larger than the intended jet hole to clean out and smooth the inside before using the proper bit to size the jet. Also after sizing the jet. You can look at the water flow and see when you have a good even flow. If the hole isn't right you can see the turbulent flow.
 
Information also at Model-A.org, link below.

Left hand margin "Component details" then select the jet "Main", "cap", "comp", or "idle" and you will get the specifics for each jet, function, installation, orifice size, resizing info , desired flow rate in milliliters per minute), and more.

http://model-a.org/default.html
 
Here is my flow tester. Does not need any pumps, pvc pipe etc. Just an old milk carton, rubber tubing and some plywood. It is just as acurate as any other but simple KISS.

Bob
flowtest01.jpg
 
Attached photos are of a jet flow test stand I built a number of years ago and have used continually. It has a 36" water column. The pump is a water fountain pump obtainable from Home Depot. To mount the jets I purchased some water faucet blank screw-on devices and drilled and tapped them A valve is included to turn the flow to the jet on and off. The water column is mounted to a discarded Model A brake drum.

Tom Endy
 

Attachments

  • flow test stand-1.jpg
    flow test stand-1.jpg
    66 KB · Views: 64
  • flow test stand-2.jpg
    flow test stand-2.jpg
    58.5 KB · Views: 57
ItsA31 said:
Lowering the float level a little will make it run leaner. Not a jet solution, but food for thought...
Click to expand...

I do run my float just a little low, but have never had any of the problems that I read about, like dyeing at a stop or problems on an incline.;)
 
[QUOTE
Are you using the same carb now that was on it when it was purring like a kitten? [/QUOTE]


No, and that's what is making me crazy. I did get the engine built in Turlock and he did an exceptional job. The rub is that he used his carburetor and distributor on a stand. He fires them up and runs them for a while to check them out and warm them up before they go out the door. I also think he likes the look on the customers face when their new engine is running like a Swiss watch in front of them.
I know that I would have a really great carburetor if I were to be showing off my work, and I'm guessing it is perfect for his shop at sea level.
Just for the record, I couldn't be happier with the engine, and though I did have trouble getting it running correctly due to a pile of warped manifolds, the folks at Berts in Denver faced the set on my car.
I pulled them in their parking lot and had them done in just a few minutes and back on. It was great to have anything you might need right there, and they bent over backwards to accommodate me, what a great experience and group of folks.
 
One more messages of thanks to all of you who helped and especially those who sent me the PM's and web sites and picture/descriptions of your flow appliances, they are really going to help.
This is the information I was looking for and there is a mountain of it. Tapping this resource has always impressed me and the folks here are really the greatest, thanks again and I hope you all know how valuable this is for everyone, so again thank you for taking the time and putting out the effort to help put the pieces together,,, again!
 
You must log in or register to reply here.
Back
Top