HELP: My 86 Mariner 75 hp 4 cylinder has performed without problems for over 16 years. I have not been able to use it as much as years past. The last time I was out, it started like a champ, as usual, it ran great at a wide open throttle and any cruse speed on plane. It runs good at low rpm speeds not on plane, but it dies at around 1000 to 1300 rpm at trolling speed or "no wake"speed. It sarts back up fine but will die every couple of hundred feet. (it just quits) I had it out today with fresh gas, proper Quicksilver oil and Quicksilver fuel treatment. The same problem is happening again. I have Left out the "Oil Blend" device and just mixed oil in the gas like the old days. I though possibly the "Oil Blend" could have been the culprit. The "Oil Blend" has always worked fine also.(I have always winterized the Oil Blend and checked it to insure correct operation per Mercury's instructions) Is it possible I need a carburator rebuild or do I have some other issue? The only real shop work I have ever had done was a new water pump rebuild twice, just to keep a fresh impeller in place.