Spark problems are a noticeable miss, not an "engine dies" situation. I would guess that you have a bad warm-up regulator. You are getting a puff from the cold start valve and fire, but then the control pressure is too high to keep it going.

There are lots of posts on this. Bottom line is that you need to check your cold control pressure with a gauge.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe