engine problems

[danom]

Hi all New here. Was just given a 30ft 1979 Reinell. It has twin 228 mercruisers with 350 chev power. Boat passed survey with flying colors and has also been inspected for charter service, altho I wont be chartering. Boat has not been run for approx. 6 months. So out I go with new batteries and bunch of tools, am quite mechanically inclined, install new batteries and start both engines. Very little coaxing required. Run beautifully, smooth, no vibrations at all. After 30 min of high idling 1000 rpm, the port engine shut down and would not start. When it shut down it was like someone turned the key off. After 40 mins. the starboard engine also shut down. Tried to restart starboard side engine and it would fire up for about 2-3 seconds and shut down. As I have been doing some reading on this I would like to eliminate the simple stuff first. I can tell by age,paint and stuff the port coil may be suspect so taking out one today. As for the starboard engine I am thinking gas issue so will take filters and check lines as I suspect vapor locking there. Reason I wrote all this was in hope some of the people on here could encountered some of these thinks and could help me out. Anyone here??
Thanks very much for the long post. Sorry Dave