Yanmar 3GMF: Mystery Drop in RPMs

[casey1999]

Originally Posted by CapitainMike

Some fuel tanks have a filter in the bottom of the tank on the outlet fuel pipe. If you can check the filter could be partially blocked. alternatively and may be also you have fuel lines that are breaking up in side causing a blockage.

You are correct on the fuel filter at bottom of the tank. After buying my boat, we moved it to its new slip. We were having problems with the engine stalling. It turned out the screen at the bottom of the tank fuel outlet pipe was totally blocked. I removed the 20 gallon tank and cleaned it. I also cleaned all the filters. The stuff doing the clogging was a black substance (maybe bacteria). I used a biocide with the new fuel. After one year I see the tank has this same black substance on the bottom. It has not made it to the screen. I plan to polish the fuel in the tank to try to remove this material.

As you suggest, I think I will replace my old fuel lines- maybe the inside is falling apart. Any ideas what the black stuff is that I get in my tank?

Also, what effect would a valve adjustment (engine) have if the valve clearances are way out of spec?

[CapitainMike]

Originally Posted by casey1999

You are correct on the fuel filter at bottom of the tank. After buying my boat, we moved it to its new slip. We were having problems with the engine stalling. It turned out the screen at the bottom of the tank fuel outlet pipe was totally blocked. I removed the 20 gallon tank and cleaned it. I also cleaned all the filters. The stuff doing the clogging was a black substance (maybe bacteria). I used a biocide with the new fuel. After one year I see the tank has this same black substance on the bottom. It has not made it to the screen. I plan to polish the fuel in the tank to try to remove this material.

As you suggest, I think I will replace my old fuel lines- maybe the inside is falling apart. Any ideas what the black stuff is that I get in my tank?

Also, what effect would a valve adjustment (engine) have if the valve clearances are way out of spec?

Send me your normal email address in a private mail and I will send you two Pdf files that might help you You are supposed to put some in every time you fill up an if you keep diesel in plastic containers them also.

If you are going to take your tank out again fit a small sump and a drain off tap to it.