ZZR 600 had a set of shims available to go under the needle retaining clip to give a similar effect. The shims were a given thickness so as to enrichen the fuel flow and negate the effects of aftermarket pipes weakening the mixture and avoiding creating a stumble on acceleration.
Amost certainly pilot jets. You need to poke them through with copper wire. Air, ultrasonic cleaned just dont work.
The Mikuni BST36's have several grooves at the top of the needle to make the adjustment. It is the last tuning point on these carbs, The pilots are to set the idle mixture. The main jets are to set the upper range. Setting the needle height tunes out the flat spot in between. If you change either the mains or the pilots, this may need attention. I like Mikuni's because, they made provision for this by providing an adjustment there. ...J.D.
Thank you for the interest gents. J D I’ve ruled out the ignition – starts and behaves normally using the choke Eldon Proper tank is on a shelf. Feeding fuel directly into the carbs from a small plastic mower tank J D Was running great when put away 2 years ago. A sticking float valve in July means that all I’ve done is change all 4 float valves
But is the correct fuel tap a vacuum operated one i.e. not constant gravity fed? By the sound of it your fuel supply is now constant which the system may not be able to accept.
t552 - your a star. I think you have found the issue. Not had a lot of time today but have removed one and it was blocked Will be back out there tomorrow....
