I loose rpms and power once the fuel tank gets to 1/4 or below. I got a new ethanol friendly fuel line installed last fall. Now it seems that once I have a low tank and try to get it on plane I loose power. It first occurred this April but I thought I had gunk in the tank over the winter and when the motor was running I suck some of it into the motor. I changed the plugs and filled the tank right to the top and it worked well.
In July I started to notice surging at the higher rpm range. It gets worse as the tank goes lower.

I really think the mechanic made the fuel line in the tank too short or long and when the gas moves in the tank when I start going on plane the motor doesn't suck in the gas well.

Problem #2
I just started to use ringfree and I do see residue being discharged. Something that has happened is that it feels like the motor coughs out some crud then runs fine when the tank is filler above 1/2 way. I run 87 oct gas and sometimes 89 oct and use stabil 360 as of last summer. Before that I always ran stabil marine. I winterize the boat properly and store it in a heat location over the winter. The spark plugs are more black and wet not chard on grey or black dust.
Thanks in advance.