2016 75HP 4 stroke Mercury

by Lee
(Dauphin Island, AL USA)

Engine has approx 140 hours, it had full 100 hour service at about 80 hours. When it runs for an hour, it develops a miss. At wide open throttle it (mostly) runs clean. But when I back down to about 4800 rpm, it starts to sputter. Its about every 5-10 seconds, it will miss and drop to about 4400 rpm. When I go to an idle, it will vibrate and miss.. Its done a version of this since new. They couldn't find a problem when in for service. It seems to be an issue after it warms up and is run for an hour.

All I know to try is changing the fuel filter. It site for 3 months max during the off season. I only use non-ethanol fuel.
Anything I can check, or advice, would be greatly appreciated.
Thanks,
Lee Mc