Bleeding a Yanmar 2QM20

This is pretty much an FYI post, as it took me a while to figure this out. This is NOT the procedure in the manual, but works a ton better!

Basically there are TWO places to bleed it, labeled here.


  • First, crack the screw labeled ‘1’ while hammering on the manual little pump handle. Once fuel with no bubbles comes out, crack it tight.
  • Then do the same to the nut labeled ‘2’. This one is not mentioned in the service manual for some reason! Once this is complete, you should be able to start and run the engine fine.




  1. Hi Matt, Happy to find your blog after your salmon fishing posts on SV Violet Hour. I too have a 2QM20 (in my 78 C&C 34) and wish I had seen this post just a week ago. I spent most of the day sunday trying to get my engine to start after cleaning my Raycor fuel filter. I eventually figured out how to get the air out, but it took a long time.

    • Hi, thanks for reading!

      Yes – it’s annoying hey? It took me hours and hours the first time round. Hence the post. The C&C 34’s a great boat!

  2. Yes, it was most frustrating. There is actually a short Yanmar user pamphlet on my boat that I eventually found which describes how to completely remove all air from the fuel system . If I recall correctly, It says to:
    1. open the screw you have labeled #2 and pump until fuel comes out, then tighten #2
    2. open the junction that at the fuel filter that goes to the fuel pump. Open what you have as #1 and pump until fuel comes out of #1, then tighten #1 and then tighten the junction at the filter.
    3. loosen the nipple where the fuel enters the injector, engage the decompression leaver, and turn the manual crank 20 times ( I don’t have a manual crank so i just turned engine over for a few seconds)
    4. tighten the nipple, disengage the decompression leaver and start the engine

  3. For 3., looking at the user manual now, I think this could be the nipple at the “fuel return pipe.” The nipple is just fore of the air intake. I’ll try and capture an image of the pamphlet when I get a chance.

  4. Also, the bleedvalve at the dieselpump is NOT mentioned in the manual. That took me a couple of days to realise last summer….

  5. Thank you so much guys ,just like others here I’ve spent hours upon hrs trying to bleed my 2qm20 the last 2 days with no success but this info is giving me hope and I realize my mistake was so simple ,embarrassingly simple but in my defense I’ve never had to bleed a diesel.Anyways I will go back with new hope today and try again.ill keep yall posted on my progress.

  6. Mat are you certain that photo is acurate? Just wondering if with #2 you’ve circled the wrong screw and if you meant the little screw hex nut/Phillips screw driver next to the screws with fuel lines ? Also on #1 ,if you meant the tiny (similar) scew on top of the bigger one you’ve circled?

    • Honestly, I don’t actually remember, it was a while ago and I have had a new boat for a few years… I think either would work from what you’ve described

      • Well yes it would, accept that those 2 points have copper washers which in my experience can be very delicate and sensitive repeated open and closing. So in light of this I will follow youw recomendations but with the exception of bleeding through the other points. Thanks for getting back to me so promptly,I really appreciate your input as it’s quick a challenge to find info on this older engine

        • Yes, I would avoid loosening/tightening anything with copper washers – if you can avoid it by doing another screw I’d definitely do that! Probably should edit this page but hopefully people read the comments

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