Author Topic: Brian Rupnow Modification to my simple carburetor design  (Read 9426 times)

Offline cfellows

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Brian Rupnow Modification to my simple carburetor design
« on: December 23, 2014, 08:27:54 PM »
Brian Rupnow has come up with a pretty nifty design alteration to my carburetor design.  His modification allows the throttle setting to go from idle to full open with just a quarter turn.  It also eliminates the threads in the venturi and any complications that introduces.  The PDF file is attached and can be rotated around in 3D for views from all angles... Thanks Brian!

Chuck
So many projects, so little time...

Offline Jasonb

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Re: Brian Rupnow Modification to my simple carburetor design
« Reply #1 on: December 23, 2014, 08:46:43 PM »
As the groove is not helical is there not a tendancy for the lever to bind at anything other than the position shown on the PDF?

Online Brian Rupnow

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Re: Brian Rupnow Modification to my simple carburetor design
« Reply #2 on: December 23, 2014, 09:21:44 PM »
The drawing that was posted here was incorrect and has been reposted.
« Last Edit: December 24, 2014, 01:14:02 AM by Brian Rupnow »

Online Brian Rupnow

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Re: Brian Rupnow Modification to my simple carburetor design
« Reply #3 on: December 23, 2014, 09:42:51 PM »
Maybe it's only my computer, but when I click on the link Chuck posted, all I get is a blank sheet with ENABLE 3D VIEW inside a blue box. If I click around on the blank page, a sub menu will open up at the bottom of the page with a "save" icon on it. If you save it to your desk-top and then open it, you will have the 3d view and you can then rotate it and view it from all sides.

Offline ozzie46

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Re: Brian Rupnow Modification to my simple carburetor design
« Reply #4 on: December 23, 2014, 11:44:15 PM »
  Brian, which pdf reader are you using.If I open it up in Foxit reader I get the same thing, but if I open it up in Adobe reader it works fine. 3D pdfs have to be read in Adobe Reader AFAIK.

  Ron

Online Brian Rupnow

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Re: Brian Rupnow Modification to my simple carburetor design
« Reply #5 on: December 24, 2014, 12:25:48 AM »
Whoops!!! I had it wrong. I had to get my model steam winch down off the shelf and have a second look at this mechanism. I had it "sorta" right, but not quite. The diagonal slot goes in the throttle shaft. A #5 or #6 shcs. has the end turned down to 1/16" diameter and is threaded into a tapped hole in the carburetor body, with the turned down portion extending into the diagonal slot in the shaft. The nut just locks the bolt in position. The barrel with the diagonal slot cut half way through it gets made a bit longer and the handle Loctites into a hole in the extended end of it.
« Last Edit: December 24, 2014, 01:14:29 AM by Brian Rupnow »

Online Brian Rupnow

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Re: Brian Rupnow Modification to my simple carburetor design
« Reply #6 on: December 24, 2014, 01:17:58 AM »
Here is  the corrected 3D pdf and the model showing all of the parts but with the carburetor body hidden.---Sorry Chuck---My imagination ran away with me earlier. The concept was good but the application needed to be tweaked.
« Last Edit: December 24, 2014, 01:23:00 AM by Brian Rupnow »

Online Brian Rupnow

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Re: Brian Rupnow Modification to my simple carburetor design
« Reply #7 on: December 24, 2014, 01:50:54 AM »
Here we go--This will sort things out.

Offline Jasonb

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Re: Brian Rupnow Modification to my simple carburetor design
« Reply #8 on: December 24, 2014, 07:38:52 AM »
Thats more like it

But I do wonder if the vibration from the engine will have a tendancy to make the top heavy leaver work its way downwards and constantly want to open the throttle.

I would tend to make it more like an RC slide carb where the barrel pulls straight out. Have the slot in the carb body run inline with the barrel, a short stud screwed into the barrel then the handle can screw onto the stud, a slight turn will loosen the handle so you can then use it to pull/push the barrel and then nip it back up in the desired position.
« Last Edit: December 24, 2014, 08:04:35 AM by Jasonb »

Offline Ian S C

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Re: Brian Rupnow Modification to my simple carburetor design
« Reply #9 on: December 24, 2014, 01:15:38 PM »
Jason, your design,but make the slot a helix, so that as you move the lever, it screws ouy/in, might give more accurate control.  Maybe not.
Ian S C

Offline Jasonb

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Re: Brian Rupnow Modification to my simple carburetor design
« Reply #10 on: December 24, 2014, 01:26:35 PM »
I was trying to keep it simple as not many have the facility to machine a helix, though it could probably be done on a rotary table by moving the Y axis a set amount for each 1degree of rotation if the slot were a slightly larger dia than the stud

Online Brian Rupnow

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Re: Brian Rupnow Modification to my simple carburetor design
« Reply #11 on: December 24, 2014, 04:14:37 PM »
The latest design I posted does not require a helix, just an angled slot cut into the shaft. I have no machinery here to cut a helix.  I may build one of these carbs to my new design after Christmas. I have no need for another carburetor right now, but the design intrigues me. In fact I may just build a new body for the Chuck Fellows carb I already have and re-use the needle valve and spray bar.

Online Brian Rupnow

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Re: Brian Rupnow Modification to my simple carburetor design
« Reply #12 on: December 25, 2014, 04:39:22 PM »
I really like the simplicity of Chucks carburetor, and the throttle as Chuck designed it does work. I know, I have built it and ran it on my different engines, even have a video of it somewhere. I am going to make a new carb with the modification shown, just to see how well it works and sooner or later I will try it on my Fat flywheeled Webster. I want everybody to remember--the Carburetor is Chuck's design. I am only claiming "design rights" of the different throttle mechanism.---Brian

Online Brian Rupnow

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Re: Brian Rupnow Modification to my simple carburetor design
« Reply #13 on: December 28, 2014, 04:35:03 PM »
I have built a new body and throttle mechanism based on what is shown in the drawing, and it does work quite well. I can not finish the carburetor today, because I have no brass to make the spray bar and my supplier is closed until tomorrow or Tuesday. The plan is to test it on my "Fat flywheeled Webster" engine and report here on how well (or how not well) it actually works.

Online Brian Rupnow

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Re: Brian Rupnow Modification to my simple carburetor design
« Reply #14 on: December 29, 2014, 10:20:57 PM »
Today I finished the new "Chuck Fellows Carburetor", with the modified throttle on it. That is Chucks's original design on the right , with a little handle added to the #8 shcs. That carburetor works great, but since the throttle is a #8-32 capscrew, it only opens 1/32" for each 360 degrees of rotation. On an engine running with no load, half a turn of the screw (.0156" travel) will take an engine from idle to "frighteningly fast". However, as I found out by experimenting with the carburetor on my side valve engine, if the engine is running under load, the screw will have to be opened 2 or even 3 full turns to give the engine enough air and fuel though-put to rev up. I was trying to come up with a design whereby a rotation of 90 to 180 degrees would take the throttle from fully closed to "wide open". The new design seems to work well (I will post a video) but as yet I haven't tried it on an engine. I have a good video of Chucks original carburetor running on my Webster engine,and hopefully tomorrow I will mount the new design carburetor on the Webster and see how it actually works. There is very little difference in the physical size of the two carburetors, and a very nice thing about Chucks carburetor is that there is almost no soldering required---in fact, the only soldering required is attaching the sewing needle to the knurled needle jet handle.