Appreciate the feedback so far!
I guess my main question is what am I missing with vacuum? I mean, I now understand vacuum better, more vacuum means more air/fuel pulled through, hence why the lack of vacuum would cause a stutter (some things take time to sink in!)
So,
No obvious fuel issue from the tank as breather hose blows through and there’s no gasp as you open the tank. I ran the engine with the fuel valve closed to drain the filter/pump and watch the pump fill up again and it did so pretty proficiently!
The air box is clear without obstruction and the new (white plastic, metal grilled paper finned) filter has done maybe 150 miles.
I tried the pilot screws down to 1 turn though they seemed to toughen the idle so I’ve turn the pilot screws to 3 turns out which seemed smoother, and then loosened the idle screw off to get the idle back to 1150-1250 rpm, then checked the balance and the TPS. TPS is at 5000.
I then ran the engine and sprayed engine start and WD40 around all the seals/connectors to see there was any surge in power/leaks allowing the spray to get in, and there was no obvious difference (just the constant little surge in revs off idle that happens which can also be seen in the video below) I did this also when I refitted the cleaned out carbs, as had seen that on the forum here
The Balance and throttle response is as below in attached video.
After rebalance and increasing pilot screw turns, I did go for a little ride, and there is some improvement to the low Rev stutter, but still evident.
I have still to check float bowl levels, but finding a plastic flexi tube has been a bit of a challenge today!
Is there anything blatantly obvious/simple I’m missing to create more vacuum? Does a video of the engine running give anything away?
Again, many thanks for your time and responses.