Trouble starting

Can anyone help??.Iv'e got a problem with my 1979 z650b.Firstly,it has bellmouths and drag pipes with short baffles.Runs and ticks over fine,but in order to start it I have to blow down the two rubber pipes(not even sure what they're for if I'm honest) situated on the carb main bodies between 1&2 and 3&4 carbs.No amount of kicking will get even a murmur till I do this,then it will fire up first kick.
I bought the bike like it is a long time ago.The previous owner fitted 110 main jets and 15 pilots.The needle circlips are fitted 4th groove from the top with one groove below.When I was setting my float heights yesterday I used the petrol tank I have fitted to feed into float bowls and it does so absolutely fine,so no problem there.
Really can't think where to go next and feel I could end up on a wild goose chase!.The carbs are the ones with the mixture screws fitted on the top of the carb not in bowls.

By blowing down the vent pipes you are forcing fuel into it. Does it start ok when warm? If it does then your issue is with the enricher / choke circuit.
The choke circuit is fairly simple. By lifting the choke you are opening the enricher tube and a vacuum sucks fuel through the tiny hole in the enricher tubes and it enters directly into the carb throat. Two things that could stop that happening is the tiny enricher holes are blocked or the vacuum is sucking air in through the top of the choke lifters.
A, ensure the enricher tubd holes are clear. B, ensure the choke lifters are air tight. They have o rings which go brittle.

Thankyou for that.Yes,once the engine is warm,it will fire up fine.Shall check out choke system.