Only way I can start my S2 is to crank it over while someone holds down the flap on the air meter

Makes no difference hot or cold.
No fuel is getting to the injectors from the metering head. Anyone got any ideas. Could it be a vacuum leak , knackered metering head , poor mixture.
Just changed fuel filter and fuel pump relay. Had new plugs , leads and dizzy cap / rotor arm last year. Still running mfi.
Would be glad to hear from anyone who has had similar issues.
Doing my head in a bit now