Fuel pump...while on water with motor cowl off and airbox removed, duplicate the problem. Once it starts to act up spray carb throat with a little gas. If if speeds up and takes off replace pump and you are done. May need two people to do it safely.

Also if you can pull plug wires one by one while it's acting up and see if any do not make a difference, that will tell you if it's a fire/ cylinder issue. Highly doubtful but possible. Use insulated pliers unless u like being bit by the spark.

Sent from my SM-G950U using Crappie.com Fishing mobile app