Help With Carburetor Rebuild - Duplex Improved (Simmons)

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GEmering
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Help With Carburetor Rebuild - Duplex Improved (Simmons)

Post by GEmering » Tue Oct 01, 2019 4:57 pm

I would like to rebuild the carb on my 1924 Touring.
The carburetor is a Duplex Improved manufactured by Simmons.
I would like to find and buy a new needle and seat.
Can anyone help point me in the right direction?
Langs does not have.

Gene
Gene Emering
Newton, New Jersey

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Mark Gregush
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Re: Help With Carburetor Rebuild - Duplex Improved (Simmons)

Post by Mark Gregush » Wed Oct 02, 2019 12:37 am

You can polish up the needle. The needle and seat are not available from the suppliers. Jack Darron that made the needles passed away back in 2017. If your needle is really buggered up, you can cut down an NH one and re-point it. The seat is a bit different then stock NH, enough so, that the NH can't be substituted. If the flapper is there and in good shape it is a good start. If it is missing, I would suggest shelving the project and find a different carb. If you are not sure what the flapper is, I suggest googling; mtfca; Simmons or Western Auto Carburetor.
I know the voices aren't real but damn they have some good ideas! :roll:

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Re: Help With Carburetor Rebuild - Duplex Improved (Simmons)

Post by Kenny Edmondson » Tue Oct 08, 2019 9:47 am

All the parts are interchangeable with a Holley NH. Including the needle and seat. The differences is the main jet and needle are shorter due to not having the drop like in a NH. You must have a good flapper behind the choke flap for the carb to operate properly. Contact me off line if you need other help.

I think Larry Smith was making the original style needle and seats, not Jack Daron.

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Re: Help With Carburetor Rebuild - Duplex Improved (Simmons)

Post by Mark Gregush » Tue Oct 08, 2019 11:01 am

The seat is different then stock NH. I got my needle from Jack. Here is a side by side of the Simmons/Western Auto and NH carb needle seat/jet. The short one is Simmons/Western Auto. The Simmons/Western Auto has approx .505 length tube and the NH is approx .640. The base that screws in is the same both, but the angle of the dish is different. Sorry about the QT of the shots, best I could do with my camera at close range. Small change/addition; the needle does not go down to the seat in the Simmons/Western Auto, it is a jet. The needle seat is a brass insert in the neck.
Attachments
DSCF7231.JPG
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Last edited by Mark Gregush on Tue Oct 08, 2019 10:08 pm, edited 2 times in total.
I know the voices aren't real but damn they have some good ideas! :roll:

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Mark Gregush
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Re: Help With Carburetor Rebuild - Duplex Improved (Simmons)

Post by Mark Gregush » Tue Oct 08, 2019 9:08 pm

Is this helping? Do you have any questions?
I know the voices aren't real but damn they have some good ideas! :roll:

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Re: Help With Carburetor Rebuild - Duplex Improved (Simmons)

Post by GEmering » Tue Oct 08, 2019 11:08 pm

Mark,
Too much time at work and not enough time reading the forum.
Thank you!
Great help!!

Gene
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Re: Help With Carburetor Rebuild - Duplex Improved (Simmons)

Post by Mark Gregush » Wed Oct 09, 2019 1:58 am

If you need any more info we will try and help.
I know the voices aren't real but damn they have some good ideas! :roll:

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Doug Keppler
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Re: Help With Carburetor Rebuild - Duplex Improved (Simmons)

Post by Doug Keppler » Wed Oct 09, 2019 7:31 am

I have a question, why is that part behind the choke flap called a flapper? Is it suppose to move or is it a stationary part and what is its function?
1924 Touring car
There's No Substitute for Proper Lubrication

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Re: Help With Carburetor Rebuild - Duplex Improved (Simmons)

Post by Mark Gregush » Wed Oct 09, 2019 11:06 am

It moves. As the air speed increases it is pulled open. At idle it is mostly closed but is free to swing as needed and gives a richer mixture. The Kingston l thru L4 used about the same thing, only instead of hanging vertical it lays flat. Reports I have read says it gives a better bottom end over the NH straight thru. It is not just a flat piece of metal, it is a counter weighted white metal casting so should not take a lot of air movement to open and stay as needed. I am guessing the flapper also helps with directing the air flow at low speeds over the fuel orifice/jet in the throat and may help with atomizing of fuel and venturi affect.
I know the voices aren't real but damn they have some good ideas! :roll:

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Re: Help With Carburetor Rebuild - Duplex Improved (Simmons)

Post by Corey Walker » Wed Oct 09, 2019 1:35 pm

Here is a drawing I made from an original and one that I made that seems to work fine. I don’t think I was finished Roth it when I took the picture.
Attachments
572FAF57-CD7F-4402-B479-F3DF9440BF2B.png
EAC241E2-A443-4321-99E7-6DDEB4D5BDF1.png
99F6990F-CFF6-4617-BA67-035248E06743.png
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Re: Help With Carburetor Rebuild - Duplex Improved (Simmons)

Post by Kenny Edmondson » Wed Oct 09, 2019 6:05 pm

Mark, your picture is the main jet (or spray nozzle). The mixture screw is sometimes referred to as the spray needle. The correct reference to “needle and seat” refers to the valve parts that control the maximum amount of fuel that can enter the carb controlled by the float.


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Re: Help With Carburetor Rebuild - Duplex Improved (Simmons)

Post by Kenny Edmondson » Wed Oct 09, 2019 6:19 pm

The NH’s had an idle circuit. Probably to get around patent issues the Simmons style carbs had the flapper to create a little vacuum in front of the main jet for the idle fuel. I’ve successfully made some flaps, but the counter weight is critical. Too heavy and the mixture screw has to be leaned out to idle correctly but the engine starves for fuel at higher RPMs. Just the opposite happens if too light.
If I could find someone that casts zinc or what ever the white metal is, I’d have some made. I had a place in Chicago cast some but they used lead and were too heavy, plus I was afraid they wouldn’t hold up.

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Re: Help With Carburetor Rebuild - Duplex Improved (Simmons)

Post by Mark Gregush » Thu Oct 10, 2019 1:19 am

Very true re needle and seat. If Gene is asking about the float valve needle and seat, the NH ones will work. Sorry if I was going the wrong direction, I call it a float valve. The spray needle came to mind because I have seen so many missing.
I know the voices aren't real but damn they have some good ideas! :roll:

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Re: Help With Carburetor Rebuild - Duplex Improved (Simmons)

Post by Doug Keppler » Tue Oct 15, 2019 7:32 am

I am currently working on this carb with Gene, does anyone have a float setting spec for it. Also when I removed the float needle seat there were 3 gaskets on the seat. Is this right, why would the seat need to be shimmed like that? Thanks
1924 Touring car
There's No Substitute for Proper Lubrication

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Re: Help With Carburetor Rebuild - Duplex Improved (Simmons)

Post by Mark Gregush » Tue Oct 15, 2019 12:10 pm

The float level should be the same a NH. Re the gaskets, could be a different float valve was used at some point and needed the extra to get to match up or old gaskets were not removed and over time there were 3. If you have an NH float valve you might compare with the one you took out of the Simmons.
http://www.mtfca.com/discus/messages/25 ... 1338313676
I know the voices aren't real but damn they have some good ideas! :roll:

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Re: Help With Carburetor Rebuild - Duplex Improved (Simmons)

Post by Corey Walker » Tue Oct 15, 2019 12:59 pm

Here is a picture I took about a year ago of parts I took out of a Simmons compared with the same new NH parts. The seat body is .030” longer, but I can’t say if it was original. It probably was. Then a picture of a Simmons with a new NH seat with only one gasket. It worked fine.
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A0524E02-DDD4-4A8F-A60B-06FFF7A7356F.png
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Re: Help With Carburetor Rebuild - Duplex Improved (Simmons)

Post by Mark Gregush » Tue Oct 15, 2019 9:33 pm

Thanks Corey, re the float valve. I did not know that. Everything I have read in the past indicated all parts but the spray needle and jet were the same as NH. While it might not be be the original valve, I will pull mine and compare.
I pulled the one out of mine. It is the same length as the other NH float valves I have. Could it have been a replacement, who knows. As long as the needle rides on the bendable tab on the float and remains so when adjusted, should work fine.
I know the voices aren't real but damn they have some good ideas! :roll:

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