KZ 900 1976 choke starter plungers

The choke enricher plunger rarely goes wrong, you say leak does this mean coming out of overflow tubes and ending up on the floor, if so jog the mechanic out of it and either do the job yourself or a new mechanic, allen performance in the uk is best for parts in europe, they will sell the jets and other parts if you need them, get a workshop manual preferably a haynes as this will cover the europe specs , normally jets don't need replacing unless someone has been at them with wire of some description, check jet sizes and pilot screw adjustments along with jet needle and clip groove. also join the Z1 owners club in the UK there will be a wealth of information and help from the guys on there, it would also be helpful if you could be clearer with what is actually happening with your bike. I guess you have a Z900 A4 and it should have vm26 carbs with a pilot screw underneath on the engine side, float height 22mm though it's better to set them up on the bench then if they leak you have them already off and its easier to cure the problem,, main jet 115r, pilot 17.5, jet needle 5dl31 with the clip on groove 3, pilot screws around 1 an 1/4 turns out +or- 1/8 of a turn, can i assume you have the original airbox and a halfway decent exhaust system, hopefully this will help you along the way

The stock KZ900 has 26mm Mukuni carbs with overflow circuits.
When fuel for whatever reason keeps running into the float bowl causing the fuel level to keep on rising. a functioning -- unclogged -- overflow circuit is supposed to allow rising fuel to escape before getting high enough to enter the carb bore.

The excess fuel escapes through the hole at the top of the overflow tube, runs down the tube and exits from the nipple on the outside bottom of the float bowl, and usually from the nipple on through a rubber hose routed for discharge underneath the bike.

This is a typical overflow tube:





Good Fortune!

All as you say, original airbox and original z1000 4-2 pipes that have always worked. I can't check the carb settings now as the mechanic is closed for 1 week holidays. The bike was repaired and taken through its technical test successfully. The carbs had a refurb kit, re assembled and balanced. They were fine on arrival but started leaking pretty quickly and I lost a cylinder. The carbs were wet underneath the bowls. I noticed the plugs were sooted badly so I took it back to the workshop. The carbs have been refitted 3 times now and adjustments have been made to the clip position. The mech. Says it runs good for a bit then starts to get rough - always super rich with black plugs. It's guzzling fuel. This is all I know until he opens again in a week Monday. I'm worried that there could be fuel in the crank oil.

Also yes, it is a kz900 a4, the carb specs/jet specs are as you say. All original factory dimensions.

Sounds like the float levels and/or float level valves, schoolboy error to not address this whilst on the bench, crankcase could be full of petrol,

This is another excellent example of why I do all my own work on my bike! Ed