TBH, as most of the carbs I work on are worn, I roughly balance them on tickover, then wind both throttle screws up quite a way. (Things getting noisier now!) and balance them at higher revs. Once they are balanced at higher revs, I then turn the engine off, reconnect the linkages and wind both throttles back down an equal amount to get to somewhere near tickover. I then restart the engine and use the throttle screws to sort it out as a "best fit". It may be a bit lumpy but at least I know that once beans are given it should drive OK.
Only problem happens if you get a flat spot off tickover as a result. This was/is the problem with wifey's Porsche copy, with twin Weber downdraughts, although a lot of the prob is the dizzy. The stupid garage got a so-called expert to play with the tune, totally unasked for by us, when they were failing in successfully changing the clutch plate. As a result, once it got warm I was a liability driving the semi-auto car home in second. The flt spot was like the top of table mountain, and no chance of revving it up to get it to take off, due to the semi-auto!
Sooooooo! As with much in life, tune is often a compromise and it is obvious one carb is worn more than the other. Get the mixtures right and you will be a lot better off!
Looking forward to hearing how it goes once you have the flipping tools. To think an SU can more or less be tuned with fingers and a screwdriver.
Ideally this is what is needed!
https://www.ebay.co.uk/i/2336316965...MI7pKo5-3m7AIVg7p3Ch2oCgZzEAQYBCABEgKZwfD_BwE
But the price, especially courriered to France!
AND it might not fit his manifold,