How to bleed the fuel system

[Pat McCartin]

This tutorial should help most owners bleed the fuel system of air with little trouble.

Yanmar YS, QM, GM, HM, YM series engines.

1) make sure the fuel tank valve is closed.

2) go to the highest point in the fuel system
1GM, 2GM, all YM's, QM's, and YS series this will be the on engine fuel filter.
** 3GM(?) series, omit this step (skip to #7) **

3) Open the 12mm headed screw, just a turn or two.
** DON'T TOUCH THE 10MM SCREW ** this can lead to a $100 failure

4) find the manual priming lever and test push it down.
It should travel ~3/4 of an inch full travel. If it doesn't open the decompression levers and rotate the engine 1 full revolution. Test again for travel. When you are testing you will feel two different levels of resistance. It will first travel about 1/3 stroke verry easy. Then it will get hard to push.
It will feel like 5 ft/lbs then 20 ft/lbs are required.

5) pump the priming lever until solid fuel is coming out of the 12mm screw at the fuel filter.

6) Close the 12mm screw on the fuel filter housing.

7) Find the 10mm bleed port on the fuel line going to the injection pump.

8) Open the 10mm bolt just a few turns

9) Pump the manual priming lever untill solid fuel is discharged from the 10mm bolt.

10) tighten the 10mm bolt.

open the tank valve!!
Your done.

edit;
99% of the time there is no reason to crack the high pressure fuel lines at the injectors.

 

[Ed Schenck]

Nice Pat, very well done. But are not all YM's self-bleeding? My 3YM30 certainly is.

 

[Pat McCartin]

Nice Pat, very well done. But are not all YM's self-bleeding? My 3YM30 certainly is.

they are, but it can take awhile with a dry bowl. Helping the process speeds start up.

 

[gmeyerga]

thanks, but what is the $100 failure if one touches the 10 mm screw?

 

[Paul F]

Not a QM engine

Your example may be fine for another engine but it is not the Yanmar QM engine. Please see the diagram below. Also bleeding procedure from the service manual. You are right about the little bleed screw on the top of the secondary fuel filter. It will strip the threads very easily. The fix is to ad a nut on the other side of the filter cap. Also on the return fuel line back to the fuel filter, it is much better to reroute this line back to the fuel tank. Keeping the line above the engine so that excess fuel and air is returned to the tank and not recirculated back to the fuel filter.

 

[Pat McCartin]

Your example may be fine for another engine but it is not the Yanmar QM engine. Please see the diagram below.

now that would depend on which QM you are referring to. You are aware there are 3 models arn't you? (your picture is a 2QM15)

heres a picture of a 3QM30

you are aware that the fuel filter, lift pump and injection pumps on all of these engine are nearly identical. Well except for the single cylinders.

 

[Pat McCartin]

thanks, but what is the $100 failure if one touches the 10 mm screw?

the 10mm screw has a tendency to pull the threads out of the housing if over tightened. Your better to just not touch it.

 

[JustDucky]

the 10mm screw has a tendency to pull the threads out of the housing if over tightened. Your better to just not touch it.

I wish this advice was given about 1 year ago. I had to replace the whole assembly because of the striped threads.

 

[Richard Bryer]

I missed you around for a spell there, Pat- good to see you back

 

[Mulf]

I'm confused by Step 1 and the comment after step 10.

"1) make sure the fuel tank valve is open."

"10) tighten the 10mm bolt.

open the tank valve!!"

If I followed step one the tank valve is already open, what am I missing?

 

[Pat McCartin]

"1) make sure the fuel tank valve is open."

"10) tighten the 10mm bolt.

open the tank valve!!"

If I followed step one the tank valve is already open, what am I missing?

edited, thanks

 

[Joe Mullee]

The "$100 Failure"

3) Open the 12mm headed screw, just a turn or two.
** DON'T TOUCH THE 10MM SCREW ** this can lead to a $100 failure



Hey Pat,

I made that $100 mistake two years ago and had to purchase and mount an entire new unit. Just curious, is there any way to seal up that hole to make the old unit useable again?

Thanks,
Joe Mullee

 

[Paul F]

As posted earlier, what I have done is to put a nut on the inside of the cap to seal the 10mm bleeding screw/bolt. This is the bleed screw/bolt I continue to use. The 12mm bolt is originally used on my engine to return excess fuel from the injectors via banjo fittings. On the advice of a Yanmar mechanic this excess fuel line has been rerouted to return to the fuel tank. The 12mm bolt is sealed tight on my application.

 

[Pat McCartin]

3) Open the 12mm headed screw, just a turn or two.
** DON'T TOUCH THE 10MM SCREW ** this can lead to a $100 failure



Hey Pat,

I made that $100 mistake two years ago and had to purchase and mount an entire new unit. Just curious, is there any way to seal up that hole to make the old unit useable again?

Thanks,
Joe Mullee

you can drill it out and retap to a fractional size. It's 1/4 or 5/16. I don't remember. It's been a few years thanks to good teaching.