Bongo Fury

my freeda has started to misfire, i dont know if that is possible with a diesel but thats what it feels like, i start her up and thats no problem then about 5 seconds later the miss kicks in, it might just do it the once or it might do it quite a lot more, if i give it a rev it goes away and doesnt come back untill the next time she is started, it runs like a dream apart from that. a neighbour reckons its sucking air into the system, but would it do it all the time if that was the case? could it be the heater plugs? or anything else ? any ideas.

Glow plug on its way/gone.

Or water in the fuel!

OR it is sucking air into the system check the small rubber fuel connector which is hidden behind the inlet manifold and caries unused fuel back to the tank.