Having a fiddle with a set of webers...

and actually ending up with them running better than they did at the start

Took a little courage to do this as the last time I played with them I had to take it to the car doctors to put it right...

Now the carbs are balanced and they don't spit so much.

Result!

I can think of several things - but nothing to do with cars

Did you use the tacho method? it is satisfying when you get it right

Yes, tacho method for the idle jets.

I have a balance meter which I used to get both carbs close to drawing the same amount of air.

Then I wound all the idle jets right in, recording the number of turns for each cylinder.

Wound them back out 1.5 turns each and started her up. There was lots of popping through the exhaust and spitting through the carbs at this point as it seams that 1.5 turns is not enough in my case.

I then went through each idle jet in turn winding it out until the max revs were reached, backing off with the idle screw when needed.

Then I checked the balance again, and replaced the trumpet socks on 2 and 3 that I had removed to get the balance right.

Then I went through the jets one more time and set the idle speed to 950 (ish) with the fan running.

Job done!