YSM12 Troubles

[Captain_Bill]

I am sure this topic has been discussed but I have not found it in the search so here it is again, my apologies for redundancy. I have an 80s model Yanmar YSM 12. Been a great motor for the last two years, always cranked and ran like a dream. I had to re-thread the return line (small metal tube coming from the injector) because the hole in the filter housing striped. That done I re installed, bled the lines and she popped off today. Needless to say I was ecstatic until throttled her up and she became erratic and eventually dying out. She continues to start and will idle without trouble but as soon as I throttle up she revs, loses her momentum and dies again. I have bled the lines many times and have never had this problem before, like I said she ran like a champ. Have I missed something?

 

[seanshine]

Sounds like the fuel injector pump needs tweaked a bit. Just make small adjustments on the screw until you find what works for you. Normally the punch mark on the screw is facing the bow. SS

 

[kloudie1]

Rule of troubleshooting: if it was working before ya worked on it and it isn't now, something that was worked on is very close to the problem.. What you describe sounds like a small air leak into the fuel system. It probably is around the filter, but could be either end of the line you were re-threading. The lead case would be not enough fuel getting to the injector, so a blockage (metal filing from re-thread?) or an air leak is where I'd be looking. If it re-cranks correctly after another line bleeding, it is an air leak.

 

[Jalepeno]

Probably a leak allowing air into the system. My YSM12 fuel return is connected to the fuel tank so small amounts of air can escape the fuel system. Not a good idea to connect it back to the filter. Also all Yanmar threads are metric.

 

[Captain_Bill]

Aggravated, the fuel system on this motor is not rocket science. I have tapped and put helicoils into the top (return line threaded hole and the bleeder hole) making sure both are tightened down with banjo washers top and bottom on the return line and one on the bleeder screw. I have bled the lines up to and back from the injector. Thinking everything would be right as rain I cranked it up (cranks easy). Then I went to throttle it up and the same thing is happening, at higher rps it wants to quit on me. It will idle all day long without a miss but once I put some rpm's behind it it begins to rev up then poops out.

So question...how can I find the leak if it is in fact in the housing. I am assuming the leak is pulling air IN TO the filter and not spewing out as I would be able to see fuel coming out. I would think it bad to try the soapy water treatment looking for air being pushed out. She is so close to running like the dream she has always been. Aggravated.