That is not a starter motor problem,I once had the same problem with a Ford Granada it was o.k. when it had cooled down just for 10 minutes,nobody could tell me what it was unless I was hooked up to fault finder,one day in the middle of a town it cut out and wouldnt restart,green flag came to tow me home and while we were going home he asked what the trouble was,I told him and he said it sounds like the ignition booster was faulty,got a new one fitted and no more trouble.