misfire on 1.8 gti dx engine

done 300 miles on a fully rebuild engine, on sunday i did a 70 mile trip, 10 miles left and the engine starting to misfire
i  have changed plugs and leads for new and no different have check distributor cap looks fine anyone got any ideas?
thanks

Best to check the compression next just for piece of mind.

Otherwise it must be a fueling issue.

will check the compression i hope its ok after spending a fortune on the engine most of the fuel system is new, new tank, pump, accumulator, fuel lines, fuel filter only thing i haven't changed is the injectors.