50 hp Merc wont plane consistently

[Sandbassin]

50 horse mercury on a 17.5 ft aluminum boat will start and idle fine. Itll cruise at lower speeds but the past two trips, I'll hammer the throttle down and the engine revs but my speed doesn't increase. Thinking spun hub but.... after I motor around for about 10 min and playing with the throttle itll suddenly catch and take off and get up to speed and plane out. I cant figure it out. Any ideas and help is greatly appreciated. I've already searched threads and cant find a similar issue for comparison.

 

[Texasmark]

Mark the rear of the prop from the spline all the way out to the outer shell. Run it hard. Remove it and look to see if your mark is still a straight line. If not you do have a slipping hub. Old rubber hubs have to be pressed in. Some new hubs have replaceable inserts. With what you said I'd bet you have a rubber hub as that's how they act.

 

[Sandbassin]

Thanks man. Ive already researched that and I'll try this weekend but I called a prop shop this week and the dude said once your hub goes it's done so I didnt pursue that course. And on a side note the boat was my friends and I used it regularly in exchange for just running it and cleaning it up. He didnt use it often and the exact same issue occurred every spring on the first run and the carbs would clean up and itd run fine into plane after I just ran the crap out of it. So I was split between a lack of fuel and dirty carbs or the hub. Replaced the plugs last year. I'll try your trick this weekend

 

[Texasmark]

In the process of going from holding to needing to being replaced, old style pressed in rubber hubs will slip and catch. New insert hubs are brass fingers and plastic. Seems to me, for a hub to fail, the plastic has to break....meaning a total failure....opinion. Ran newer hubs but never struck anything.