i have a 1995 6hp mercury. it just started acting up. starts and idles fine, but when you throttle up, theres nothing there. it dies if you dont throttle down. the kicker is that it only does it about every 3rd time out. never will do it twice in a row. good plugs, wires, new gas, seafoam, new fuel filter and i even cleaned out my gas tank, which was only 3 months old. any ideas?