I bought a 1448 jon boat and a 1980's Yamaha built Mariner 25hp. The model/serial is Mariner 25M/ 695 s 022240. I changed the plugs and cleaned the carb when I got it last year in about april. It would fire on the 1st or second pull with the choke pulled and start on the third pull every time when cold. Once warmed up it would start on the first pull. Took it out the other day and it'll still fire on about the third pull, but I have had to pull the rope numerous times to get it running. I've also lost a mph or two on top end and with a full load takes quite a while to plane off.
I checked the plugs and they were a tad oily, not to bad though. The gap in the plugs was maybe a thousandths to big which I adjusted. Why has it got hard to start? The tank, fuel lines, and prime bulb are less than two years old.
I've been watching some youtube videos about small motors and I think that maybe the fuel pump diaphram may be bad.
What say you guys?