l had a tough time starting the engineit sounded like it was not running on all cylinderswhen running sounded rough did have it running about 3000 rpmand then it slowly died out.pump throttle when dying but still could not save it from dyingdid get it goingagain briefly and that was it l killed the battery

Can you add some details, this is too vague.

Ok, first, pull the spark plugs, check their condition, look for signs of flooding. Next, look for water in the fuel, check filters for signs of water. If you have a water seperator(every boat should), replace the filter. Check fuel pressure to the carb, to eliminate the fuel pump. Try this, and get back to me.

Your details r a little vague but l will try & give u a few places to look.First u need to check to see if u r getting any fuel (or too much fuel).If too much ur needle & seat in ur carb r stuck open.If no fuel stuck closed.Then check for spark. l suggest u remove the distributor cap and
clean it.If u have fuel & spark it will start.It does sound like
you have a fuel problem because u said it did start,just would not stay running. l would check this first.Good luck.

if its a mercruiser there are two fuel pumps. the first is located away from the engine and is an electric pump. one or both may be bad. if you use fuel with methanol, it may be a water problem. are you using a water preventer such as Starbrite each time you fuel up? for more help check online at Marine engines .com.