Fuel problem?
 

1985 500 SEL
Starts easly and can run all day without a problem. But if I start up and run for more than 15 mins, the stop the engine for about 15 mins then re-start (re-starts easly) run for 2-3 mins the stop dead. To re-start again it take about 5mins of grinding the starter finnally it starts and runs fine.
I have repalaced the check-valve and filter, no help althouth I do think it idles better now.
Can anybody help me?