1998 Yamaha 115hp just started cutting out.

Hi guys

Was out on the water this morning, everything started of fine. Went to my fishing spot 13km from launch with no issues to report, moved around a bit with no issues once again. Weather turned a wee bit and decided to call it a day and head in. Motor started fine. Opened up got on plane then lost power. Check the primer bulb and it felt soft. Gave it a few bumps, starts up start going again. Check if all fuel fitting are inserted properly, checked the vent etc. All was well. Tested at low speed, same story run for a few minutes then dies. Open tank cap to make sure its venting. Seems like I'm getting fuel. Anyways use auxiliary to get back. Start up at home to flush and seems ok maybe bit on the rough side. So figure haven't change plugs, so put some new ones in just incase I had a dead plug (none looked bad). Not sure if the soft bulb is a new or not. Always goes hard when priming not sure if it stayed hard though. Anyways after changing plugs ran the motor for 10min up and down in revs and she didn't die. Check all fuel lines for holes and leaks with no clear culprit.

Any of you guys have any other suggestions what to look at. Just worried its a under load issue and it gets me again on the next fishing trip

Couple of things to check

Are both cylinder heads getting to running temp?

When you squeeze the primer while the boat is on the trailer do you see or smell gas?

Thanks for the reply Chris. Can't answer regarding both heads getting up to temp. Will only be able to check that tomorrow, if not what could it be?
Nope can't smell gas or see any obvious leaks

Just to add. Went and check primer bulb again now and its still pretty firm from pumping about 2hrs ago, which suggests no leaks

Hold pressure on the squeeze ball and see if it collapses slowly.

A cold cylinder head can be a stuck T-stat or bad water jacket gasket. When this happens the engine will condensate water in the combustion chamber and put the spark out in one or both cylinders.

Troubleshoot in series beginning w/fuel system....assuming all plugs have spark. Testing when not under load will garner different results, hence no issue when on muffs. Test under load and when experiencing the loss of power, start squeezing the primer. If the motor responds...bad fuel pump. If it doesn’t respond....pull carbs and clean including pull each jet and clear. Reinstall and test under load.