9.9hp Yamaha...gasping for air?

Hey guys,

Got the boat out on the water this Sunday, finally. The boat had been sitting since May of last year. Ran the motor in the driveway on Saturday with no issues. Sunday morning, get the boat in the water, fire up the motor and start running for 5-10 down the lake. Then the motor shut off and wouldn't start back up for awhile. Right before it shut off, the best way I can describe it is it clunked and shut off. I know that's not the best description for it, but it kind of knocked and off. I let is sit for a 10-15 mins and was able to start it up, but after a minute or so, it shut off again. Let it sit for awhile and fished for an hour or so and decided to take her back in since I had made it a decent distance from the ramp and didn't want to risk draining my batteries before I made it back. On the way back in, I checked the ball and noticed it was loose, so I pumped it up until it was tight and I was able to get it fired back up, but it would still only run for a minute or 2 then cut off. This time it sounded like it was gasping for air. My buddy thinks there's a possibility of trash in the line, bad gas or something related to fuel pickup. The fuel line running from my gas tank to the motor is pretty old, could it be losing compression keeping fuel from reaching the motor. Or anything else I should check before I take it somewhere to get serviced?

This motor is a 2000 Yamaha 9.9hp 4 stroke. It hasn't been serviced in years, but probably doesn't have 10hrs on it since that last service. It also sat from 2014-2023 inside and the gas had been run out of it prior to putting it away back in 2014.

Have you tried running it on a different tank and line with fresh fuel? That will eliminate a couple possibilities. You mentioned old fuel line some of that stuff doesn't mix well with ethanol and if any fuel was left sitting in that line for all those years it could break down.

Is the vent on the fuel tank open?

1st thing I would do is simple, check the compression.

Take apart + clean the carburetor. If it's stored with old gas for even a little bit that could be enough to clog the jets or needle intake valve. If stored or tipped the wrong way the oil could get into the carb. If you hear a sucking sound coming from the tank when priming the bulb then replace the fuel line or connections to the tank/motor.

Could be a dozen things........
Clogged carb.
Bad fuel pump or hard diaphragm.
Bad coil, electrical system that creates spark.
Clogged vent on tank
Leaking exhaust gasket pumping exhaust under cover

Next time it quits, bring a spare plug and pull one wire and ground plug to head and turn over motor see if you have spark. If yes then unscrew carb float bowl drain screw and see if its full of gas. If yes then get a service manual and go down the list.