40ids

[one-two]

Hi, am I right in thinking that the enrichment feature on these carbs is the little copper tube that feeds into the secondary venturi? Why - in very simple terms - is that? What would happen if it went into the main choke instead? Would it make a difference? Thanks for any ideas.

[Fritz A. Ficke]

You are right, the tube into the secondary venturi is the enrichment circut. Which makes an IDS from a IDA. I do not know for sure but would it not be very difficult to not have it dump fuel at the lower speeds if it went into the main venturi? The idea remember is to make an over rich fuel mixture at wide opeon throttle to prevent detanation caused by heads that really were designd to be twin plugged at that compreasion ratio (which Porsche changed in the 2.2L and later cars to eliminate that issue).

[Steve@Rennsport]

Hi:

Those auxiliary fuel nozzles were VERY carefully positioned by Weber to ensure proper fuel atomization by aiming them at the aux venturies.

If you reposition them to shoot directly down the throat, you will partially drown the engine at WOT as liquid fuel will not be mixed with air. You get a big stumble.

Been there, tried that, a very long time ago.

[one-two]

Thank you both. It's really great to draw on others' knowledge. We have been experiencing a flat spot and I think this is probably part of the problem. We got into all this by fitting the taller aux venturi. Next issue is how to reinstall the cutoff copper tube!

[911pcars]

Another reason. Air flow is the fastest in the smaller venturi. Thus the signal to draw fuel from the float bowl occurs sooner. Same reason why the main discharge tube is positioned in the secondary venturi.

Sherwood