Pierburg 1b3 tacho needle fluctuates

Got the pierburg 1b3 carb, engine is fully warm and choke is off. At ideal the tacho needle fluctuates up and down. Tried adjusting the idle bypass screw to fully in with co2 screw wound out to compensate and it still does it, so feel like it's not any of the screws on the carb itself. Seems to do it no matter what at idle.

Any ideas? Is it ignition timing being off? I always found ignition timing changed with a strobe light if I adjusted the fuel mixture, so bit lost on which I should do to get it idling smoothly.

Also drinks fuel like George Best drank alcohol, so hoping I can get the bloody thing sorted out.