I noticed that someone already has found the progression on the idle downsizing for you with the 60/105 combination and has tried to lean the idle down.
I don't know if it is the volume of fuel that is making the idle too rich or the ratio of the fuel to the air corrector?
I have to PRESUME that the original .70/1.20 combination is the right ratio since that came from Weber directly? I'm thinking though that because the application was for a VW Dune Buggy, Weber may have intentionally jetted them heavy to avoid an unmuffled open header from "leaning out" the engine under wide open throttle usage?
It isn't coincidental that Holley does that with the "double-pumper" series and that is their explanation for those carbs having a "heavy idle". The Holley idle can be leaned out by increasing the size of the idle air restriction which is Holley's version of an "air corrector".
The math that I have for the combinations of leaning the idle down more using the original Weber proportion is as follows:
60/102
55/95
50/85
45/77
40/68
If I was STILL adventurous, I would explore if these combinations are available (they are) and test them to see if they would work?
The .40 aren't quite 1/2 of the original .70's but pretty close. I find it difficult to conceive that those would work at all considering that the 70/120 was originally for VW 4 cylinder Dune Buggies, but the process is usually that when you find something that will work like the 60/105 like you have, you keep going one step at a time until it no longer does work and back off
It is entirely possible that the 60/105 that you have now is as low as the idle jets can go but you won't know that until you try to go lower, one step at a time?
So the first question is will the next size smaller work and if it does, how rich is the idle? Does it make the idle cleaner?
You need to check with Weber jet suppliers to see what is available now to see if that is feasible before you start. All these combinations now seem to be available.
It's just a thought, but this is how you determine if you have reached the optimal tuning.
According to Alfa1750's ad, holders are available now all the way down to .40. The fuel jets as well.
https://www.ebay.com/itm/29178...7:g:TP4AAOxynwlTcmKD
I'm just trying to be helpful and anticipate your questions.