I changed plugs,cap,wires fuel filter,water seperater and still no luck. tried a few small things with the carb. also.
since it was done by a shop that you trust it was probably done right, i would still change or at least check for water in the filters, you might have trash in carb and do for a rebuild, you might go back to the shop and talk with them since you took it there for this problem and see if they had found any water in the filters or maybe something they had over looked.1985 sea ray 21 ft cuddy cabin 350 mercruiser 260 hp alpha drive. it runs great until you try to go fast then it spits and sputters but doesnt stall out. every once and a while it will run ok then take it out again and it starts doing it. The tune up was done by a marine shop just for maintinace reasons. Like I said this happened before the end of last season and a fuel/water seperater seemed to take care of the problem.