Are you getting fuel supply all the way to the filter on the motor ? If so check your fuel bulb for cracks or that it isn't collapsing at speed.

Unless you want to throw parts at it you�ll need a tech to run it hooked up to the computer.

But I agree you�re on the right track. Here is a way to determine which it is if you just are the DIY type.


https://goneoutdoors.com/test-yamaha-outboard-fuel-pump-7875483.html

If it is like my ox66 Yamaha 200 it has low pressure pumps that work off a vacuum at idle to supply fuel and push fuel up in the high pressure tank. The high pressure pump is electric but attached to a tank that contains this filter. It's really more of a screen than filter but will clog up with carbon and trash from the fuel. You can clean this filter but I would change it out. I would also change plugs. I'm not sure how the 02 sensor works on a sho but mine has a sniffer in a tube on the block and it also builds up with carbon and has to be cleaned out occasionally. All of the above can contribute/cause the symptoms you are describing. All of the maintenance on these items is easy to perform yourself and can save you some serious money up front and down the road. Hope this helps

Certainly check the fuel water situation. I had something weird like this and it ended up being the fuel lines. It's a simple place to start looking.