Can I improve Yanmar YM 13 (20GM) performance?

[blan321]

I have had problems this year with tubeworm growth on prop which reduced engine rpm in gear from 3500 max to 3200, and then picked up weed on prop crossing Chichester bar, seen at fuel pontoon, caused drop of 200 rpm as it picked up weed. Engine yanmar 2gm20. Do check prop and hull for fouling first!
My understanding of the mechanical fuel pump is that if the rubber diaphragm fails then fuel may enter engine sump. I think they are quite robust tho. Lever arm failure I think very unlikely. Many people fit an electric fuel pump to help with bleeding and as backup. So your mechanical pump may well be fine. Easy to test tho, disconnect outflow and pump by hand, check lever is off the cam. If fuel squirts out likely to be fine.....

 

[SvenH]

The cable connections have been checked and are ok.
Prop was clean for the last 10 seasons, i'm sure it is now too.

The thing that remains is that the rpms always go back up again.

I did check the tightness of connections in the fuel line, those at the extra fuel pump were easy to tighten a bit more.
All the others were quite solid.

 

[Glenlivet]

Have you checked for blockage/restriction at the fuel tank breather?

 

[mcalan]

I have a very similar issue with mt yanmar 2mg the revs for no apparent reason drop this is not a misfire or a cough and I can increase them again manually ? Really. Not sure what could be the cause.

 

[SvenH]

Thanks for all the pointers guys. Much appreciated.

Went for another sail after clearing some liquid from the breather tube to the tank.

Instead of being better the engine fluctuated more and did not get above 2800 rpm.
At the moment of motoring out between to dams it stopped running.

Had it done so seconds earlier it would have been a difficult situation very quickly.
We were able to set sail rather quickly and sail clear from the dam and and prohibited are just beyond.

After something like 15 minutes I tried starting again and it fired immediately, maybe a hint slow but it is a quick starter anyway.

Went to a marina close by and did some checks and the engine started every time and ran no problem.
We then decided to head back to our own marina which also went well.

Today I started preparing for fuel line replacement and found the lift pump at least doing a bit of pumping.
But in removing the fuel line to it, I found I could move the inlet connector to the lift pump rather easily, it was a bit loose.

So that needs tightening. I'll be fitting new copper washers.

I have not found any of the typical signs of lift pump failure but I also could not find an interval on replacing the lift pump. Is no such interval mentioned anywhere?

Another thing is that the electric fuel lift pump between engine and tank was not working, both not being connected correctly electrically and malfunctioning.

So I will reconnect everything without the electric pump and see how that goes.

Is there anything I need to think about when reconnecting stuff that is easy to overlook for a noob like me?

 

[SvenH]

Continuing... ( I enjoy reading other peoples troubles and potential solutions so thought to update)

As part of maintenance my folding prop needs replacing. Turns out, the one being replaced is 15 x 9" which must mean that the its predecessor may be the 15x12.
anyway, I found a maxprop which has changeable pitch.

And that brings me to the regulator.

I spoke to two yanmar mechanics that suggested the option that the varying of engine revs can come from a groove worn in to bits in the regulator.
I'm going to check if parts are still available but besides, if I change the prop pitch, the engine load will change, right?

Does that also mean that the regulator will run in a position it previously did not, and that the revs dropping behavior may change too?
Any ideas to the pitch to choose?