Coil slow to heat up and cool down

[Jay Cat.30]

My engine would run fine for an hour to an hour and a half then slow to half speed for 5 min. then die. The engine would not restart for up to an hour and a half after dying. Checked coil for spark and would only get maybe a 1/16" orange spark max when hot. Replaced coil and all is great. Now get almost 3/4" blue spark after long run times.

Jay