weber conversion

Have just fitted a 32/34 weber to my 1.8 clipper.
All seemed well got it ticking over and revving fine.
Its fine under steady acceleration but any more and it feels like its not getting enough fuel or air as it starts
judder as if its running out of fuel.
Have tried adjusting it with the mixture screw but it doesnt have much effect. Have read about about 1/4 turn adjustment but
i can turn mine 3 or 4 times with no real difference to the sound of the engine or tickover speed.
Any advice or suggestions would be great
Thanks

The ideas that spring to mind:

Try restricting the return fuel line - (I restricted mine on my old rocco to 1.5mm after replacing the swirl pot and ending up with insufficient fuel pressure)

I presume the pump itself is OK?

Check the ignition timing too.

Other possibility is an air or vac leak.