Wont idle after warming up

[Joelindsay10]

1997 merc 5.7, runs great for first hour, then won't idle and skips intermittently

 

[Scott06]

1997 merc 5.7, runs great for first hour, then won't idle and skips intermittently

Would look at

fuel filter empty and look at contents
ignition system what is condition of cap rotor plug wires and plugs. Assume you have a thunderbolt ignition . May want to look at sensor in distributor especially if it has the exposed terminals which is the older design.
try opening gas cap when this happens might be the vent line is plugged and after a while it pulls a vacuum on fuel tank
possible carb rebuild but wouldnt think it would run ok for an hour if carb was gummed up