Mercury 650 cough at idle..

[jak3]

Hey guys, recently picked this 1968 Mercury 650 4cyl for my pontoon boat. It ran great at the guys house, fired up every time. Took it out to the river and ran it for a while and it ran great. Shut it off and it would not fire. It took me 10 minutes of fiddling to finally get it to start and idle. It now has this weird cough when I finally get it to idle.. I'm thinking I may have gotten bad 87 at the pump or maybe the fuel filter is clogged and that could be the reason why it's so hard to start? I have a video of the cough here- https://youtu.be/2MmHE-8-qgk?t=25s

I have 0 knowledge on outboards, was hoping someone could help.

Thanks

 

[SuperEnzo]

Does your pontoon have a portable or built in gas tank? I had an outboard that made the exact same "sneezes" that your outboard is having and it was due to an air leak from the gas tank. The fuel line from the tank to the outboard was leaking at the connector and sucking in air, causing it to sneeze just like this. Check the fuel lines and connectors for leaks