2006 90 hp Yamaha 4 stroke

After running for a few minutes, motor intermittently bogs down & loses power. Starts fine, idles and slow speed fine. Already changed fuel and plugs. Any expert advice for a novice? I have to wait 3 weeks before the local boat shop can diagnose it and I’m not sure they’ll be able to do so in the regular boat “tub” they test in. If they have to take it to the river, I’ll be looking at a $300 fee for diagnosis. Trying to do everything I can before going that route.

Seems that the fuel lines on many tanks are suspect nowadays due to fuel formulations. If the liner separates and fails it will block fuel flow. It should be easily diagnosed with some exploratory surgery, just cut the end off to look inside, and re-connect with a clamp if it's good. If it's separating it will be obvious.

Good luck!