Author Topic: Building small carburetor with throttle  (Read 12407 times)

Online Brian Rupnow

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Re: Building small carburetor with throttle
« Reply #15 on: December 15, 2014, 01:22:29 AM »
This is what a view "down the hole" looks like from the intake side, with the throttle barrel in place and drilled out to finished size. I'm pleased. There is no "step" evident, just a nice smooth taper almost up to the throttle barrel, then a plain round hole with parallel sides all the way out thru the rear (threaded side) of the carburetor. There isn't a lot of "meat" left between the root of the 5/16" external thread and the 0.195" diameter thru hole, only about .035" wall thickness at the root of the thread.---However, this is enough, although I wouldn't want to crank very much torque on that carburetor body when assembling it to the intake manifold. A view from the rear side shows that the hole ended up nicely concentric to the outside threaded diameter---Something I always hope for, but don't always achieve.


Online Jasonb

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Re: Building small carburetor with throttle
« Reply #16 on: December 15, 2014, 07:57:38 AM »
Good to see you have upped the bore, no doubt did not want to make a smaller taper bit ;)

I suppose its a legacy from using quite a coarse thread on the engine, When I make carbs that screw on and that is mostof teh ones on the hit & miss engines which tend to mount via a lenth of tube I tend to use 40tip threads. May be worth adding a note to your drawing if you are going to share them that a finer thread may be a bit stronger if starting from scratch or just the plain spigot option?

J

Online Brian Rupnow

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Re: Building small carburetor with throttle
« Reply #17 on: December 15, 2014, 05:17:05 PM »
Of course, every carburetor with a throttle needs a throttle handle----How else could you get your  engine make those really neat VROOM, VROOM noises. I know that the head of that air bleed screw looks awfully close to the underside of the handle, but it does clear.

Online Brian Rupnow

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Re: Building small carburetor with throttle
« Reply #18 on: December 15, 2014, 06:06:22 PM »
Moving on to the spray bar and needle valve, I am going to try something I first seen suggested by Chuck Fellows. Although I CAN drill holes smaller in diameter than 1/16" in my lathe, I am not terribly comfortable with doing so, and I often wonder what degree of concentricity I really am achieving. The local hobby shop sells rigid brass tubing which measures .062" on the outside diameter, and as far as I am able to measure, .031" inside diameter. The sewing needle in the picture measures .035" in diameter, and will fit into the end of the brass pipe about 1/4" before the diameter conflict won't let the needle go in any farther. Instead of attempting to drill a .031" hole thru the nose of the spray bar, I will drill a 1/16" diameter hole and solder a short section of this brass tube into it, and solder the needle into a threaded section with a knurled o.d. to become my needle valve.

Online Brian Rupnow

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Re: Building small carburetor with throttle
« Reply #19 on: December 15, 2014, 10:03:16 PM »
I must admit, I don't have a warm, fuzzy feeling about this upcoming silver soldering job. it sounded like a good idea, but how that I see the size of what I have to do, Oh Boy!!! Ah well, nothing ventured, nothing gained---Wish me luck!!!

Offline cfellows

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Re: Building small carburetor with throttle
« Reply #20 on: December 15, 2014, 10:19:02 PM »
Brian, I didn't use silver solder, just soft solder.  I also coated the outside of the 1/16" tube with common plumbing flux before inserting it into the large opening.
So many projects, so little time...

Online Brian Rupnow

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Re: Building small carburetor with throttle
« Reply #21 on: December 15, 2014, 11:32:56 PM »
Oh Sure Chuck!!!---Soft solder, the man says!!! You know what happens when I use soft solder, don't ya---I fill the whole friggin' carburetor full of solder. I've been down that road before. Soft solder works just great for me on copper plumbing pipe where it wicks into all the places I want it to---- on carburetors, not so much.  I like silver solder because it doesn't wick very well. The inside of that largest piece of brass is full of #10-40 threads and the outside of the smaller diameter is all #10-32 threads. if I can keep from melting that very small piece of 1/16" diameter pipe and not fill all my threads full of solder I will be amazed. It doesn't show up very well in the picture, but I did run my smallest countersink into the 1/16" diameter hole in the end of that larger piece to make a "well" around the 1/16" pipe. I REALLY want to fill that well full of solder and nothing else.

Online Brian Rupnow

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Re: Building small carburetor with throttle
« Reply #22 on: December 15, 2014, 11:58:12 PM »
This shows a method I have used (with varying success) over the years to keep silver solder out of areas I don't want it to go.  The secret seems to be in letting it dry really good before putting a torch on it. I have learned however, not to use it on knurled knobs. The Wite-Out keeps the silver solder away, but seems to flame harden into something almost ceramic like that is damned near impossible to get out of the knurling. --It can be removed easily from an external thread by running a die over it to clean it up.

Offline Stuart

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Re: Building small carburetor with throttle
« Reply #23 on: December 16, 2014, 08:22:03 AM »
Brian

Why go to all that trouble and mess , I have silver soldered nipples to 1/16 OD copper pipe without bunging up the works

Just use silver solder paste ,no flux required , no masking .

Just smear the paste on the joint before assembly and heat you will see it flash round the joint ,it will not spread like normal method can do

Now I know you are across the water cupalloys sell it but I am sure that it's available on your side , it's a bit costly but a tube lasts a ver long time

http://www.cupalloys.co.uk/low-temp-silver-solder/

Look down the page

Going on to tin lead solder that to is available as a pre mixed paste use as above but with less heat


Stuart
My aim is for a accurate part with a good finish

Online Jasonb

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Re: Building small carburetor with throttle
« Reply #24 on: December 16, 2014, 09:18:49 AM »
Or just soft solder paste it does not need the strength of silver solder, if you don't have that snip of a very small piece of soft solder sit it in your CSK and apply heat that way you just get a small amount of solder.

I drilled mine with a 0.8mm drill no problem.

Online Brian Rupnow

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Re: Building small carburetor with throttle
« Reply #25 on: December 16, 2014, 03:23:52 PM »
Jason--see previous post. Stuart--that looks very interesting. I didn't know there was such a thing. I will pursue that from my end and see if it is available here.---Brian

Online Brian Rupnow

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Re: Building small carburetor with throttle
« Reply #26 on: December 16, 2014, 04:24:12 PM »
It seems that the soldering Gods have smiled on me.--Either that or I'm getting better. I put the smallest tip I have on my oxy acetylene rig, held my breath, and actually got the silver solder where I wanted it and no where else. I did have to set the part back up in the lathe and cut away the "cone" of silver solder that formed around the 1/16" diameter pipe a little bit, but all is well. The dance isn't over yet though. I still have to solder the fuel inlet pipe to the side of the "spray bar". First though, I have to set it up in the rotary table and mill the large diameter into a hexagon.

Online Brian Rupnow

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Re: Building small carburetor with throttle
« Reply #27 on: December 16, 2014, 07:54:35 PM »
Sometimes ya just need that third hand. I bought this little gizmo at a yard sale for $2 but I see that they are still sold brand new. They really work great for soldering wires together when you need one hand for the soldering gun and one for the solder----and it's great for carburetor work. There is a 1/16" diameter hole thru the center of that fuel inlet held in the third hand, but I don't drill it completely through until all the soldering is done. If you drill it all the way through before soldering, it has a tendency to get filled with solder. After the soldering is finished I set it back up in the mill and drill it through until it breaks thru to the center of the carburetor. I'm getting very close now---All thats left to do is final assembly, determine what length the needle has to be cut to, and solder the back end of the needle to the head of the brass knurled needle valve adjuster


Online Brian Rupnow

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Re: Building small carburetor with throttle
« Reply #28 on: December 16, 2014, 07:58:16 PM »
By the way---What's a good way to get that red crap off of brass after silver soldering? I have tried scrubbing with an old toothbrush and plain water, scrubbing with an old toothbrush and silver polish, soaking the part in a 50/50 mixture of white vinegar and hydrogen peroxide, all to no avail. Short of sanding it off, I can never get rid of it.----Brian

Online Brian Rupnow

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Re: Building small carburetor with throttle
« Reply #29 on: December 16, 2014, 09:00:26 PM »
We're finished!! Okay, what can I tell you? First, how do I know how long to let the needle stick out past the tip of the brass threaded piece of the needle valve.---Well, I make sure the tip of the needle alone is seated into the hole in the inside end of that tiny 1/16" tube inside. You can tell, because it will go in about 3/16" +/- past the bottom of the hole drilled for the #10-40 threads. Then I slide the threaded brass portion down over top of the needle and screw it into the carburetor body until it absolutely won't go in any farther (finger pressure only). Then back it off two full turns. Measure how much needle sticks out past the back side of the knurled portion. That is the amount that must be cut off the rear piece of the needle. After you have cut it off (I use an abrasive wheel on my air grinder), use fine (220 to 300 grit) emery cloth to sand the last 1/4" close to where you cut it off. Those needles have some kind of clear coating on them that silver solder won't stick to. Then, making sure the needle is fully seated again, set the whole carburetor up in the vice, with the knurled brass bit unscrewed two full turns from "tight closed), and solder it. (It helps to use a countersink tool to put a small crater in the outer end of the brass knurled part for the solder to pool in around the needle). The silver solder will have a tendency to "hump up" when it flows, and you want to be able to grind it down flush on your belt sander, but enough will be left in the crater to hold the needle solidly.


 

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