stock z1 airbox and jetting

i recently acquired a z1 airbox which i intend on putting on my 76 kz900 (with 1075 kit). it has an open 4 into 1 exhaust. running a stock air filter and later style vm28's (without accel. pump), what size main jet should i use? i have never used an airbox before, always pods. not sure what i should do. thanks for the inputs.

What type VM26s are on the bike? Obviously, jetting will be relevant only to the specific type of 26s you have. If you have stock 76 VM26s, these are pretty rich from the factory. You might want to put in some #120 mains depending on the type of air filter used in the Z1 box and leave the other settings stock. If the VM26s are not 76 type, then this advice won't be right.

i intend on using the later style vm28's (without an accel. pump). would the 120's still work?