If its cutting out - then you need to see why, either no fuel/spark.
If you starter turns the engine and doesn't go (ala DPB

) grrrrrrrrrrrrnnn, then its fine.
When cranking do you get a strong smell of fuel or not?
Check the leads, rotor, dizzy - mine used to do the same thing at traffic lights about a year ago, new leads and I was fine. They're were parp and just caused it to mis-spark, so it would stall and flood the engine, then when cranking - it wouldn't fire because it was partly flooded. Left it for 3 mins and it fired right up.