loss of power - Fuel tank pick-up hose?

[blueolive28]

I'm trying to track down a loss of power with my Yanmar 315. I'm only seeing about 3500 RPM at WOT. I was able to get to 3850 at the beginning of the season. I've changed both fuel filters, and have seen on other forums that some people have issues with the fuel hose into the tank. Does anyone know if there's any type of screen or check-valve in the fuel line inside the tank? I'm trying to isolate fuel supply as a source.
THANKS!

[boatisgone]

My problem occurred with a MD7A in an 27' Ericson. Not the same, but the theory may help diagnosis.
Small diesel engine power loss:
I had a loss of power due to sucking air into the fuel line. It is harder to find an air leak into a fuel line VS a fuel leak out of a line or fitting. I installed a piece of clear fuel line just ahead of the water separator/filter. The diesel looked like soda pop when the engine was revved up. I discovered a small screen in a 90 fitting on top of the tank.
It would run ok on lower speeds, but as the suction increased the amount of air getting sucked in caused havoc
Hope this helps. John

[blueolive28]

Thanks, I ended up adding a vacuum gauge to the Racor and found that the fuel lines were reversed. I just got the boat last season and it ran fine and passed the survey with no issues, so who knows how long it was like that. Somehow it finally gave up running backwards and wouldn't return fuel. Rebuilt the filter and swapped the lines and all is good again.

[special k]

this happened to me with my 6lpa-stp. mechanics couldn't find problem so i just kept asking around . finally found a guy who found and corrected this issue. mine was the boost compensator. small device side of block. shows in my My yanmar manual. removed small cover was full of water and rust. cleaned and dried and cleared vacuum hoses and reassembled. problem was solved and oh so easy since i am not mechanically inclined. after spending $$$ for diesel techs to trouble shoot and they couldn't help, the advice of a fellow yanmar owner solved my issue. i did leave a case of beer on his boat... cheers!

[WillieC]

What a great end to the story!

I am mechanically inclined but I had an issue with a string trimmer. Thought it was gas that had soured over the winter so I spent a day fiddling with the carb, then ordered a new one and had the same problem. It would start and run, just barely. New was the same as the old. Then it came back to me from my reading that I should check the exhaust screen. I had dismissed that earlier since it ran when I shut it off last fall. Plugged solid.

I also read the same thing here and elsewhere, especially with the older little engines. A plugged exhaust elbow is a real thing that I will not so lightly dismiss moving forward. Fortunately, mine had rusted through, demanding replacement.

Nice sleuthing and good for you having enough curiosity to solve the problem with the help of your neighbor!

[Norseman]

. Thanks, I ended up adding a vacuum gauge to the Racor and found that the fuel lines were reversed.

Holly Molly..Learn something every day around here,

Happy you found it and thx for the heads up.