Weber Chokes really this bad?

[wndsnd]

Just bought some Weber Chokes.

The machining is bad and they did not chamfer the bottoms. Is Weber Quality really this bad these days, or did I get bad product.

Here are the tops. The good one is on the right. Etched from the top so you can tell what size it is from looking down the throat. Bad one on left etched from side, no use at all once installed.




Here is the bottom with no chamfer again bad on on the left.




Thanks Guys

[chris_seven]

The chokes you have don’t appear to be genuine Weber Parts which were die cast and weight reduced .



There are quite a few poor aftermarket chokes being made and the quality varies significantly.

Some of them seem to have a conical air inlet and many of them have the venturi restriction at the wrong height which affects jet calibration.

We make one that has the ideal hyperbolic inlet and the restriction at the correct height but machined from solid.

We make them for Weber, Zenith and Solex 40Pl



I am sure that PMO make them to the original design and they would work well.

[Trackrash]

Where did you get these? Even the "Weber" ones I have used are not perfect and can use some polishing, but these seem to be of poorer quality.

[wndsnd]

Gordon,

They were purchased from overseas.

On second thought, the bottom chamfer does not seem to be as important on larger chokes.

Are the cast Weber chokes chamfered on the bottom as well as the top?

[chris_seven]

The 'diffuser' section of the choke is should be at least 3 times longer that the inlet section and should taper to the same diameter as the barrel of the carb.

If you have a 40IDA3C then the 'outlet' diameter of the choke should be 40mm and the transition should be sharp and the end and not be 'chamfered'.

When fitted into place it should form a smooth and virtually imperceptible joint with the carb body.

This then effectively increases the length of the diffuser and allows a streamlined flow into the inlet port.

The inlet to the venturi isn't best described as a 'chamfer' and the ideal shape is a curve which is hyperbolic or exponential as these will provide the 'smoothest' flow over a range of air speed.

Smooth flow helps the jet to 'meter' more consistently over a broader range of air speeds.

A cone shape with a sharp transition at the point of the venturi is less ideal and will tend to work best at one air speed.

Original Venturis were pressure die cast and tend to have a short parallel section at the transition and the curve of the inlet section is also quite conical.

Now we can CNC machine shapes can be improved without cost penalty.

I am sure the differences in performance between original cast and new well machined venturis is very small but the 'improved' finish can't hurt.

The position of the venturi is important for two reasons.

The first is that it will affect the manner the pressure drop created affects the main jet and its air corrector.

This in itself isn't a big deal as jet size changes will compensate but it does make it more difficult to 'transfer' settings from one installation to another as the baseline has effectively been altered.

The second and potentially more damaging is the interaction between the auxiliary venturi and the main venturi will change and this will influence the boost effect produced by the auxiliary venturi.

I am not sure of the detailed impact in terms of boost effect per unit change of position but is will have some influence and if possible IMHO changes should be avoided.

[wndsnd]

Thanks Chris,

Your reply detail was great for me, as I have never seen the real Weber Chokes. I do have the IDA 3C's and when I took the 34's out, I thought they were original.

Your product looks nice. Are they anodized or powederpainted?

I think the 36's I bought with the rejetting will at least give me the rough answer I am looking for. Once I figure that out I will contact you for final set up.

I appreciate your help. Sorry about not knowing the correct terms. Chamfered bevel was the only thing that came to me. You do a much better job with technical accuracy! Always learn from your posts.

[wndsnd]

A local friend showed me an original casting today.

Mine are all machined aluminum. No way to tell if the CNC is correct. Anyway I decided the 36 were too big for my car. Back to the 34.

[Walt Fricke]

I am thinking that the same chokes (venturis) will physically fit either a 40mm Weber and a 46mm. But the chokes need to be different at the bottom because on the 40s they drop down into a step or something like that?

So these would be for 40s? Ones for 46s would have more tapered bottoms?

Or have I got that all mixed up in my memory?

[chris_seven]

Yes,

The 46IDA measures at 45.5mm in the region that locates the venture as the basic barrel is 46mm. The step is still present but is very small.

There is also a difference in the area where the progression holes are drilled.

I have a NOS pair of 46IDA carbs and have checked them through quite carefully.