Hello Nik,
Sounds like it could be the WRD may be stuck in the warm position, fuel starvation or the ignition points are closing up.
Make sure all the tuning items are fine first (points, battery etc). You must have a clean fuel supply with adequate pressure and volume (make sure the fuel filter, is clean). If the main fuel filter is dirty, check the main fuel tank screen and the intake screen on the electric fuel pump. Run a fuel pressure and volume check if there are any doubts about fuel delivery. Yes, check the starting aids (intake valve and the pump solenoid). Also you should monitor the WRD during the warm up cylcle to make sure it is not stuck open or closed.
What year is your W113 and what is the recent history?