Agreed - I'd be looking at the carb first since it's 1 & 2 with the issue.

Since the tappets have recently been done, I'd actually also _strongly_ urge you to recheck them. If they were adjusted to a smaller than optimal clearance, the exhausts in particular can run hotter and even potentially lead to burned valves. I don't think that it would have happened that quickly (in fact it'd be close to impossible) but you'd want to double check them to avoid leading to an issue down the track that has similar symptoms but was caused by this, not the current issue.

One of the 'big' deals with twin webers and dellortos is the linkages. Cheap ones flex to buggery, So they never open the same amount each time you move the throttle. Where it gets worse is this - you're supposed to (if you want it to run 'right' set them up with return springs on each carb throttle link arm, so that they both properly return to zero. You also need the link arms to be all on the same angle, and have the tie-rod adjusted evenly. If they can't be gotten to an even airflow, there are other tricks.

I've been meaning to do a write up on how to basically reinvent the wheel - and do the linkages properly - because probably 90% of the ones I've seen were done wrong, badly wrong.

About the worst thing commonly seen (and this is even worse on triple carbed 6cyl engines - 3 of them all uneven) is that they remove the idle rpm screw from one of the carbs, adjust the idle on the other one, then adjust the tie-rod on the second carb (with no idle rpm stop screw) until the flow is matched. The problem there is that with a little bit of heat, expansion, and already flimsy linkages, it'll return that second carb to a different idle throttle position under all these differing conditions.

If you absolutely had to utilise that option, then the trick would be to get the car right up to operating temp, and set it then and there whilst there's a fair bit of underbonnet heat. It'll be a bit rough to start, and you might need to keep the acc pedal down 1/4 of an inch or so to run it at 1500-2000rpm for the first minute or so, or when pulling up to a stop, till it warms up, but then at least the idle whilst driving it will be fine each time you pull up.

If you really want I'll do a couple of diagrams of the additions/changes to a throttle linkage n the weber/dellortos (actually it can apply to SUs too, but some of them have better linkages) so that it'll idle fine and then have near perfect opening synchronisation with each other throughout the throttle opening range.

If the linkages are strong and adjusted well, then i'd look at float level in the carb, and needle and seat condition, maybe it's close to over-filling the fuel bowl at idle due to a scored/worn needle and seat. Only IF all those turned out negative would I go to checking the idle jets etc. My bet would be the linkages/idle rpm setting. Considering how bad most of them are (even though they cost a bit, they aren't necessarily worth persevering) it's probably the most likely situation.

If you can get pics of it it'd probably help to