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706 d310 German won’t idle at startup


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I have a fully rebuilt d310, head , injectors and pump.  The first fifty engine starts were perfect, but now when I start it up and release the fuel primer (shut off pull handle) the engine sputters and dies.  If I start it up and feather the primer like a choke on a gas engine to keep it running for about 2-3 minutes and then release it, the engine idles and runs fine.  The exterior temperature has been 50 and below since I’ve had the issue, but I’m not sure if it’s temperature related.

Is this normal, or do I need to adjust something?  Any help would be appreciated.

I have about 8 hours on the rebuilt engine, head, injectors and pump.

 

 

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My 706 german does that also, but didn't do that until after rebuilt pump and injectors. Now when starting you have to leave the throttle back and hold the kill out for a bit to keep it running. The motor on mine has over 11k hours on it though.

 

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Ok, so I'm going to kind of speak out of the corner of my mouth here....

On the 4cyl version, on the kill lever (example: 84 series) it has an "OFF", "START" and "RUN" position.  In the "START" position, it changes the timing (likely retards it) to allow it to start easier.  As far as I know, the 6cyl pump does the same.  If the engine didn't do this until after the new pump was installed, I'd be questioning if it is: 1.) Timed correctly and 2.) If the advance is working properly.  

@Injpumped is this correct?  Doesn't the kill cable also change timing before shutting off the fuel? 

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Is there a trick to checking for a leak in the system.  I had the same thought that the fuel system may be getting air into it and by holding the primer lever out I am essentially letting the system build pressure and push the air out.

 

Now I just need to figure out how to check for this.

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9 hours ago, mmi said:

leak/air in system ?? by feathering valve you are keeping enough pressure /fuel in pump to work air out??

It doesn't work like that....

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The start lever is just start fuel, additional fuel for cold starting. Timing is at full retard at cranking regardless of lever positions. This one sounds like a filter base issue.

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15 minutes ago, 706German said:

Is there a trick to checking for a leak in the system.  I had the same thought that the fuel system may be getting air into it and by holding the primer lever out I am essentially letting the system build pressure and push the air out.

 

Now I just need to figure out how to check for this.

If you had a leak in the fuel system that allowed air to enter, it would suck air constantly, not just at start up, and it would always run rough with no power... not just at start up.  Also, any leak that allows air to enter will usually leak fuel when not running.  If you had this type of problem, I'm telling you, you would have power problems at all times.  You would likely also have a resting fuel leak. 

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29 minutes ago, Injpumped said:

The start lever is just start fuel, additional fuel for cold starting. Timing is at full retard at cranking regardless of lever positions. This one sounds like a filter base issue.

Ok, so get technical on me just so I know.... 

On most all pumps that I am familiar with, start fuel is maximum allowed fuel.  Is there something within that pump that allows more fuel than the fuel allowed at peak torque (full governor fuel)?  If you move the kill to "Start" position while running, the engine speeds up and changes sound regardless of throttle position.  How can it add more fuel than non running rack position? And if it's more fuel than that, how does it not over rev when moved to that position while running?

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The VA pumps inject much more fuel for starting when lever is pulled, it only works with throttle lever at low idle or up to about 1/3 way up. And it only works at low speeds, well below idle speed. So, you can't pull the start knob for more power in the field lol! What I'm talking about here is only Bosch VA pumps. Many pumps have higher fuel delivery for starting than peak torque, but many do not. Inline pumps and M100's typically have excess fuel setups for cold starting. Many inline pumps do retard timing when cranking, it's built in to the plunger design, the top of the plunger will have a notch machined to lower the top of plunger. Once plunger rotates far enough past all usable positions, the retard notch then determines the lower(later) start of injection. Clear as mud?

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6 minutes ago, Injpumped said:

Clear as mud?

Nope.  Crystal clear.  While I never worked in a pump shop, it was part of the training I received when I went to tech school.  I had to rebuild different types of pumps for my training.  That was a great explanation,  thanks!

 

I thought I remembered that some pumps could inject more fuel at starting than peak torque, but tech school was a long, long time ago, lol. 

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2 minutes ago, 706German said:

Injpumped, can you please explain the "This one sounds like a filter base issue." comment. 

I am intrigued because I do have a resting fuel leak around the secondary fuel filter that I haven't resolved yet.  

 

Sounds like you found your answer to me.  Find and fix that leak and see if the issue goes away.  

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filter seal missing, or put in the wrong place restricting flow? I'm not there looking at it, so impossible for me to figure it out. But, the symptoms you give sounds a lot like an air leak letting it drain down, and lose it's prime. 

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