Title and description says it all. The brass cylinder resting on the rim where the seal would be... goes into the hole its next to. Which way does it go in??? With the hollow part of the cylinder facing down in the hole or up. I believe the fuel flow would be coming up through that hole because the jet is in the other half of the carb and aligns with this hole.
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Except what kind of carb it is.

It's a Solex.

What Solex? If you're gonna ask for help, provide enough information to allow folks to give you a meaningful answer!

The Cap'n

OK - not sure of the type but here's a pic with identifying numbers.
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Whoa. Crazy ass carb. If I had a couple hours to kill, I'd search Google Images for Solex. Then look at the pictures until I saw one that looked like that. Look at all the little things to be sure. Then once you know the model, search for an exploded diagram and analyze that for the location of your mystery part.

Good luck!

OK - I found an exploded diagram that ThePaintedMan found for me last year when I was screwing around with my carb.
http://www.shoptalkforums.com/viewtopic.ph...64&t=139538

(I'm always posting on here about my carb... still trying to figure it out but I sure am good at taking it off and putting it on now.)

So this part is called the accel pump weight. I can see that it is meant to impede the flow of the gas shot into the primary barrel from the accelerator. The gas is flowing straight up around the "weight" so gravity is holding it down. Maybe the reason is simply to stop gas from always flowing unless you're pressing the accelerator.

So again this is a half hollowed-out, hexagon cylinder. Just trying to figure out if the hollowed-out end goes towards the flow of gas or away from it. Trying to think of the thermodynamics of it and if it even makes a difference.

Yes I could just put it in and try it but I know someone on here just knows what it's for and why and how I should put it in. I would assume other carbs have a similar flow impedance mechanism?

Here is my post last year with other pics of may carb from all different angles. I know it's a weird one. Probably pulled off an opel in a junkyard or something.
more pics of my carb from another post

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Dellortos have a similar "check valve" for the accel pump jets. In their case, it's a small ball bearing that rests underneath the hexagon shaped brass piece, but it is not hollow on either end.

Check both ends of the circuit of your carb with a flashlight to see if there is some kind of cone-shaped piece that the hexagon rod might fit over. Otherwise I'd say go with your gut and face the open end toward the flow of fuel. If it doesn't operate correctly, take the top off again and flip it. That's about the best I can think of unfortunately.3

Really? I was noodling it through in my head and thinking the solid end would go against flow because it would respond faster under accel and would "shut off" back flow into the accel pump when not under load to allow accel pump to refill with new gas.

had myself convinced that the hollow area was a way to hold gas in this chamber so that there would be less lag time waiting for gas to get to barrel during next acceleration while keeping the mass of the accel weight lower (gas weighs less than brass).

After the gas gets by the weight it has to get by the accel port jet. (another restrictive thing)

There is nothing below or above the weight that would require the hollowed out side to fit one way or another.

I think if you look at the parts diagram you can see there are 2 other critical components that I don't think have been mentioned yet. There is a spring that fits in the hollowed out section and a ball on top of that (part numbers 19 & 20). The whole thing is then turned over and inserted in the opening at the top of the body.

Hopefully when you turned the carb body over those two very small and light weight pieces didn't drop to the floor.

Jim

I hadn't gotten a chance to look at the diagram since you posted this time around, but that would be a logical reason why that area exists. Just like dellortos, the ball and spring is what acts as the check valve. Better look for them...

ah damn...

I actually had the good sense when I turned the carb upside down to do it in a controlled manner close to the ground just in case something fell out. I went back to where I did it and found the ball bearing right away. I looked three different times for a total of about one hour and finally found the spring. Got it all back to together and it seemed to work pretty well. But... now I got a gas leak I have to figure out where it's coming from.