A Sluggish F115?

[Dan in Alaska]

My 26-Foot Hewescraft has twin F115's. One engine recently started acting sluggish. It takes longer to get up to RPM than the other one. It eventually gets to WOT, but it takes 30-45 seconds longer to reach full RPM. Once up to RPM, the engine behaves normally, with no warning lights or alarms. I've checked all the easy stuff: oil change, lower unit lube, spark plugs, fuel filter, loose wire connections, etc. The spark plug in the #1 cylinder is rather "sooty" compared to the rest, so I'm thinking dirty injector? The props are the same on both engines, and I'm pretty sure they are not the culprits.

This particular engine also seems to lose prime occasionally, and I need to re-prime the fuel line with the squeeze bulb. Give it a few squeezes and everything is back to normal again. Should I be looking for a small fuel line leak somewhere, or something more sinister, like a fuel pump that's on it's way out?

[ken2]

swap fuel lines at the tank, just to rule out any problem with them.

If the issue stays with the same motor, then I'd start looking at the other fuel filters vst filters.

[welder]

Loosing prime could and probably is a bad bulb , fuel pick up tube or fuel line. As said above , swap fuel lines and run her up and see what ya get .

How many hours are on the motors and do you run any additives in the fuel system ?

[seahorse]

the dark looking plug could be a leaky injector.

Because of your sluggishness, connect a fuel pressure gauge to the diaphragm lift pump and also to the fuel rail test port and run the motor at all speeds while monitoring for any low or erratic pressure indications. Also check for a significant pressure leakdown after turning the motor off which would signify a leaking injector or a bad pressure regulator.

Hooking up a piece of clear fuel line to lift pump inlet will indicate if there are any air leaks in the boat's fuel system which could also cause a lack of power.

It's best to have a service manual handy plus an understanding of the motor's EFI system.