Carb problem on 01 5.7 merc

[chris84]

Launched boat on 5/10 ran great, last week developed hesitation when advancing throtlle and backfiring. Changed cap, rotor, and reset timing and changed water/sep filter on 6/14, took boat out for test ran great all way across bay ( 3 miles), when heading back to marina hesitated at 2600 rpm and wouldn't come up on plane eventually smoothed out and accelerated. Max rpm was only 4000, was running at 4600 2 weeks ago (for a limted time) with throttle room still left usually run at 3600. Came back to dock rechecked timing, still on. Boat backfiring when getting on throttle in neutral. Spoke to mech who had carb rebuilt in spring of 05, believes ethanol in fuel is clogging carb again and suggests another rebuild. Anything i might have missed before i pull off carb and send out myself (still have sticker shock from last season).