pull vac pipe off the fpr and crank it, heard of these failing internally and spraying fuel out vac connection making mixture too rich! obv take all precautions when doing this, try it on a cold engine and have a rag round it to soak up any fuel.
next step is to check what is actually happening when the problem occurs. check if you have spark (lay king lead on rocker cover while cranking) then check if you have fuel (whip spark plug out, see if bores smell of fuel)
