Author Topic: Model I.C. Carb with Throttle  (Read 17610 times)

Offline Roger B

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Re: Model I.C. Carb with Throttle
« Reply #30 on: March 14, 2014, 09:00:38 PM »

So many projects, so little time...

So true!
Best regards

Roger

Offline Brian Rupnow

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Re: Model I.C. Carb with Throttle
« Reply #31 on: March 14, 2014, 09:38:51 PM »
Chuck--I am going to try both carbs on the Webster. Before I even had a chance to give your carb a fair shake you had posted that you were not happy with it, so I put it in my tin full of treasures and went directly to the model airplane carb. Right now I'm doing the "One step forward-Two steps back" thing with my carb build. There is still 24" of snow here and daytime highs around +5C so I'm not in a real rush to get finished and work in my main garage---it's too cold.

Offline Brian Rupnow

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Re: Model I.C. Carb with Throttle
« Reply #32 on: March 14, 2014, 09:39:16 PM »
It's been a looooonnnng day!!!  I have remade the brass outer body to the new design, and it looks good.---But---I just found out I can not re-use the barrel. This was a case of two wrongs not making a right. When I made the first brass body, I got something off center. Scratched my head for a minute and thought--"Oh well, I'll just drill the hole thru the barrel off center a bit so it will match up".---BAD MOVE!!! Now the barrel with the off center hole won't work with the new brass body. OH POOP!!! I'm going upstairs and read for the rest of the day. Fresh start tomorrow!!!

Offline Brian Rupnow

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Re: Model I.C. Carb with Throttle
« Reply #33 on: March 16, 2014, 12:18:16 AM »
Nothing picture worthy accomplished today. I spent the whole day messing with sump pump stuff. I wasn't totally impressed with the 20 degree included angle tapered hole that I had machined on the inlet side of the new brass body. So--I turned a 20 degree included angle taper on a piece of 3/8" cold rolled and used some really coarse, nasty automobile valve grinding compound on it to hand finish (can't honestly say "lap" ) the inside of the taper. It turned out quite nice actually. I don't really have any boring tools small enough to bring this off properly.

Offline Brian Rupnow

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Re: Model I.C. Carb with Throttle
« Reply #34 on: March 16, 2014, 07:33:23 PM »
Progress has come to a stop. The new brass outer body is finished. In the process of making the new barrel, I convinced myself the safest way to ensure concentricity was to insert it firmly into the brass outer body and drill it in place. This worked fine for the 0.156" diameter thru hole. I then rejigged the part and went to spot thru the #2-56 threaded hole for the idle stop screw so I would be able to get the slot in the correct place. I opened the drawer with my 1/16" end mill in it, and guess what!!! The Shop Pixies have taken it away. I don't want to tear down my set up, so everything will set until tomorrow when I can get over to the tooling shop and buy a couple of new end mills. I can't spot thru with a drill, because it is not on the center of the 3/8" diameter steel, so a drill would slide sideways and tear up the threads in the brass part.

Offline Brian Rupnow

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Re: Model I.C. Carb with Throttle
« Reply #35 on: March 17, 2014, 03:35:23 PM »
Today we are back to the point we were at when I figured out that my first design had a fatal flaw. The carb outer body is remade, and the steel center barrel is remade as well. What a pin in the butt!!! One pic shows the assembled carb setting up posing for an "overall" shot, one shows it with the throttle closed. (The closed position is adjustable) The throttle never closes completely, otherwise the engine would stop. It is only when the carb is closed to the position showed that the air bleed screw comes into play.--And remember, since the openings in both sides of the brass barrel are the same size on each side of the throttle barrel, the amount of opening on the side closest to the cylinder head will be open exactly the same amount as the opening on the air intake side. If the engine falters when the throttle is in this closed (idle) position shown,  then the air bleed screw can be adjusted to smooth out the idle. Once the throttle is swung into a more open position, the idle circuit is blocked by the side of the barrel and has no effect on the carburetor.





Offline Brian Rupnow

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Re: Model I.C. Carb with Throttle
« Reply #36 on: March 17, 2014, 03:44:26 PM »
This is the best shot I could get of the carb with fully open throttle. What appears to be a bit of dirt right at the top of the barrel bore is actually a bit of metal displaced by the drill when I tapped the hole for the bolt holding the handle on. I will clean that up and plug it with a bit of thread sealant on the handle bolt.



Offline Brian Rupnow

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Re: Model I.C. Carb with Throttle
« Reply #37 on: March 17, 2014, 07:46:08 PM »
What you see here is a temporary disposable jig, made from aluminum. There is simply no other good way that I know of to position the two brass pieces correctly in relationship to each other, and then not have them move while silver soldering them. The jig is "temporary and disposable" because it has to be cut apart to get the soldered assembly out of the jig. The short piece of brass is for the fuel line to attach to, and has been turned to its finished size, and the hole drilled part way thru the center of it. The longer brass part is 1/4" diameter and will be turned down to finished size on each side of the fuel inlet before being threaded #10-40 on both ends. At some point while it is in the lathe chuck, the tapered end will be machined and the thru hole will be drilled. After that, the hole part way thru the short piece will be extended until it intersects with the central fuel passage.



Offline Brian Rupnow

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Re: Model I.C. Carb with Throttle
« Reply #38 on: March 17, 2014, 07:49:06 PM »
This is the result, immediately after silver soldering the joint. I hold the aluminum in an old drill press vice so I can position it in whatever way I have to so I can reach all areas of the soldered joint.



Offline Brian Rupnow

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Re: Model I.C. Carb with Throttle
« Reply #39 on: March 17, 2014, 07:51:12 PM »
And here we have the soldered part, freed from the jig and cleaned up a bit. Now I get to do some more lathe work on the main 1/4" diameter part.



Offline Brian Rupnow

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Re: Model I.C. Carb with Throttle
« Reply #40 on: March 17, 2014, 11:29:39 PM »
I've been holding my breath for the last two hours machining this fuel inlet, but I think I've got it nailed. I don't know why I hold my breath while I'm doing these really finicky things, but I bet you do too, don't you!!!





Offline Brian Rupnow

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Re: Model I.C. Carb with Throttle
« Reply #41 on: March 18, 2014, 01:38:24 PM »
WOW!!! I didn't think I was going to be able to do this. That small diameter is 0.050". The smallest thing I had ever machined before was 0.093" dia. valve stems. I used a 3/16" cold rolled rod, and put the taper on the end while the rod was still at full 3/16" diameter. Then I started turning at 1000 rpm for 1/8" at a time right down to 0.050, then move ahead and machine the next 1/8" down to 0.050. I followed the same procedure to turn the 0.100" diameter. I tried to keep all machining as close to the chuck jaws as possible. I'm not even going to try to part it off. I will use the hacksaw while it is still locked in the chuck to cut it off, then use my belt sander to cut it to length.--To keep from feeding the swarf bunnies, I will wrap a length of masking tape around the part before I cut it off.



Offline dieselpilot

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Re: Model I.C. Carb with Throttle
« Reply #42 on: March 18, 2014, 02:53:11 PM »
Model aircraft engine air bleed carbs seem to open the air bleed near half open area. You might find a rich mid range if the air bleed closes too early. Finding the sweet spot for the air bleed hole is I'm sure a matter or trial and error.

The 20 included angle on the needle will be very coarse for gasoline. The reason sewing needles work well here is due to the small taper.

Offline cfellows

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Re: Model I.C. Carb with Throttle
« Reply #43 on: March 18, 2014, 03:49:43 PM »
So, Brian, if I understand, the 1/4" rod was solid bar when you soldered the pieces together?  And the smaller piece was only partially drilled, I would guess on the outboard end?

Chuck
So many projects, so little time...

Offline Brian Rupnow

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Re: Model I.C. Carb with Throttle
« Reply #44 on: March 18, 2014, 04:13:02 PM »
That's right Chuck. I was able to use a center drill while I had the part in the chuck, and drill part way through the length before soldering. If I had drilled all the way through, it would probably have filled up with solder during the soldering operation. Then when I drilled it through in my mill as the very last operation, I didn't have to frig around finding the center of it to start the drill into.