I picked up a used 2007 8ph 4 stroke last week. The guy who sold it to me said it ran great and it started on the 1st pull. I put it on my boat hooked it up to the boats fuel tanks and ran it on a test run. started on the 1st pull and ran great. took to salmon fishing on the columbia it started the 1st day and ran for 4 hours no problems. 2nd day started on the 3rd pull smoked for just a minute then ran for 8 hours no problems. 3rd day couldn't get it to start. I did take it off the boat and laid it down on the correct side each night for security reasons? don't know if that is the problem? got home put the merc on the stand hooked up the temp tank. check the spark plugs both are sparking, fuel line is getting fuel to carb. did get the motor to start with a shot of starting fluid in spark plug hole. ran for a minute increase throttle then slowly idled down and died. won't start again even with starting fluid. where do I start looking for my problem?