2 years ago I steamed cleaned my tank-replaced the fuel lines-replace filters-tightened all fittings-put in new fuel and it ran like a charm-last year after filling up at a marina-it started running rough-I replaced both filters-now it stalls every 20 minutes-I bleed lines-it starts and stalls again after 20-30 minutes. Does anyone have an idea on what I can do and what is happening?