Okay, the disc sounds tricky. I don't suppose you could carefully solder some of the holes up, although I suppose the holes aren't in the same location though, so even if you did solder all but three holes you wouldn't have the pattern the same- which I assume is intentional in the design of the progression feed. Hmmm, tricky work.

Could you drill out the entire progression bypass and replace it with a new section? Sorta risky though.

Exactly, want to richen up the progression stage (will also need some jetting and idle air bleed mods) by reducing the number of holes to match non-emission (i.e. performance) carbs.

But, I have also read that these carbs are very good road carbs due to the style of idle and progression circuit they have, almost self-tuning in some way, just that they don't work so well on smaller bore engines.

Sorry, I'm confused what are you trying to do? Reduce the amount of progression holes as well as keeping the same arrangement or pattern between them?

Cheers, a bit of photochopping to get the pics the right size and then time to try making a disc to drop into the hole..

Here we go:

Attach file:

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  Dello 3hole.JPG (80.88 KB)

I'll go check mine, back soon.

Can anyone that has a set of "non-emission" Dellorto DHLA 40's take a picture (close up like the pic below) of the progression circuit drillings for me? Also if you have jet drills and are able to measure the sizes of them that would be even better!
Non-emission carbs should only have three holes in the progression circuit and the code should be just DHLA40 without a suffix.

Pic of emmission progression drillings, note five holes:




I have a pair of DHLA40F's that I paid pocket money for, so I want to see if I can mod them to fix the idle and progression circuit issues associated with them.
Figuring a precision sleeve for the idle air bleed and a precision disc glued into the progression circuit to convert it from 5 holes to three.