1.3 mk1 engine wont run if the brake or clutch are pressed

hi ive got a mk1 golf recently had an engine rebuild but now it runs but cuts out if the clutch or brakes are put on ?

any ideas whats causing this ?

please help   

xx

This is gonna sound whacky, but humour me….

Has the brake pressure switch wiring been somehow mixed up with idle cutoff valve on the carb i wonder?

Is the vacuum advance fitted and working?