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Losing RPM’s when in gear

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impag10

New member
I recentury purchased a 15 ft whaler with a 2013 60 HP Yamaha 4 stroke. When I bought it the engine only had 53 hours on it and it now has 69 hours and was running great. The other night it started to stutter and shut off. I figured out that there were some gaskets on the gas tank that was letting air in and the fuel line was basically sucking more air than gas, so I switched to one of my other external tanks. The rest of the night it ran fine. The next time I went out the engine would only get up to 4,000 RPM’s and seemed like it was running louder and struggling. It’s pumping plenty of water and never stuttered or sounded like it was going to stall. Back at the dock I tested it in neutral and it had no problem getting up to 6,000 RPM’s. The previous owner did install an in line fuel/water filter. Any advice is appreciated as I don’t know much about outboards, more of a sailer. Also I have been using fuel treatment and just filled the gas tank a few days prior from a station that is pretty busy so I’m guessing it’s not a fuel issue.
 
Hi impag -
I'm a sailer too, so I feel your pain. I would definitely get a water-separating fuel filter on there as quickly as you can, if for no other reason than as a troubleshooting point.

Did you check the fuel ball to see if it is collapsed when the engine stutters? If so, you may have a clogged vent on that tank, and it could be impeding the flow of fuel to the carb.

Rob
 
Rob-

There is a water-separating fuel filter installed so we are good there. Should the fuel ball feel completely full when the engine is running? I did try squeezing with the engine running and it was fairly easy to squeeze. I have a 3 tank I can attach it to and see if the vent is clogged. Thank you.
 
impag10 said:
Rob-

There is a water-separating fuel filter installed so we are good there. Should the fuel ball feel completely full when the engine is running? I did try squeezing with the engine running and it was fairly easy to squeeze. I have a 3 tank I can attach it to and see if the vent is clogged. Thank you.
Click to expand...

The fuel ball won't feel solid as there's no pump between it and the tank. It's in more of a slight vacuum state, as the fuel pump on the engine is "pulling" fuel from the tank through the fuel primer ball. Once in a while, if the vent on the tank is clogged, the primer ball can collapse as the the engine pulls more fuel than the tank can provide,a nd that causes fuel starvation. A mechanic at the shop mentioned to me that it was a common cause.

If you are comparing this to an auxiliar diesel, you'll find that outboards are not as susceptible to air in the fuel. Air in the fuel line on a diesel will pretty much shut it down, but my experience, outboards are more tolerant. But to your notes above, if it's pulling more air than gas, that'll be a problem and will likely manifest itself more under load/high rpm. Were you able to replace the gaskets and/or connections between the tank and the engine?

If you can get the engine to run reliably on one tank, but the other tank routinely causes the engine to lose power under load, it's most likely the fuel in the tank, or something about the line delivering the fuel. Ethanol has caused me a lot of problems on my carbuerated engines if they sit.
 
Rob

Thanks for the help. I think the vent was clogged. First I checked both ends of the gas line and they seemed fine. Then I completely unscrewed the vent and screwed it back in to where it still was open. As soon as I hit the throttle everything was back to normal.
 
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