I have a few sets of venturis for my Dual Weber 40 idfs. All of the vents are the same size. I was planning on boring a set of the 32mm vents to 34mm and a set to 36mm (long story why I am doing this).

My question. Is there anything special that I must do other than bore out the opening to the desired size. Do I need to shape anything or do I just simply bore it out.

I planned on doing this on a metal lathe. Obviously it would be much easier to just bore it out. If I have to shape the vents, I will just send them off.

Thanks

Just bore them out

Thank you!!!

I dont have the answer, but I would guess there is a lot of science that determines the shape of them, laminar flow, low and high pressure areas for fuel atomization etc. If a straght pipe was all that was needed, then carbs would be much cheaper and less complicated. who hasn't heard of the venturi effect? boring them out will likely change the performance characteristics of the carbs so as to make them useless.

Click to view attachment

if you just bore them out the high pressure area at the throat will be destroyed and the high pressure low pressure differential will be minimized ! My SWAG (scientific wild ass guess!)

from a random web site!

As the throttle is progressively opened, the manifold vacuum reduces since there isless restriction on airflow, reducing the flow through the idle circuit. This is where the venturi shape of the carburetor throat comes into play, due to the Bernoulli effect (i.e. as the velocity of a gas increases through a fixed orifice, its pressure falls). As the throttle valve closes when load is relaxed, the airflow through the venturi drops until the reduced pressure is insufficient to maintain load fuel flow and the idle circuit takes over again as described above.

Thats what I was thinking. I guess that I will do a simply bore in the next few weeks and see what happens. I will post my results.

I sell 36mm venturis but most people just alter the 28mm stock vents.
The shape does matter but you can get away with a fairly crude approximation.

added a little ( very little ) research to my previous post!

I'm just a new guy that is really into Weber's. Why not just buy the correct ones?

Wayne

I have extra venturis to play with. I have the tools to do the job. The main reason is that I am cheap and I like to play around with tools.

progress??