Bongo Fury

at the weekend i decided to give my bongo a small service and changed the oil and filter air filter and fuel filter,
started ok so i took it for a spin,after i got about 100yards it cut out,restarted after a few turns but felt sluggish.
it runs ok although feels sluggish but everytime i take my foot off the throttle it dies after a minute or so.
restarts eventually and carries on while driving normally until foot is taken off the throttle again.
i am stumped cos it ran really well till i serviced it
any ideas please
thanks

First guess would be the fuel filter isn't sealing properly, also be worth checking the banjo filter on top of the fuel pump.