View Full Version : Generator fuel solenoid adjustment

Richard and Rhonda
05-27-2008, 05:13 PM
As you know a diesel on off mechanism is as simple as turning the fuel supply on and off. Of course you have to crank it with the starter, but after that there is no electrical circuit to disconnect to shut it down. That happens when you turn off the fuel.

On my Yanmar motor there is a 12V solenoid that moves back and forth to actuate an arm on the fuel injector pump to allow fuel to flow or stop the fuel flow. I had a problem with a hard starting generator when the batteries were low, and I suspected low voltage had something to do with the solenoid not pulling the arm far enough open to allow fuel to flow. The solenoid is spring loaded to close the fuel arm when the solenoid is not powered. When this started happening with fully charge batteries I suspected something else.

This was not the problem. In fact I made the problem worse with my first attempt at adjusting the arm, and the adjustment is counterintuitive, that is the reason for this post.

On my system, the solenoid pulls back into itself which in turn pulls on the arm to open the fuel. There is a turnbuckle adjustment device between the solenoid and the fuel arm. This is mostly hidden by the intake manifold, BTW. So, if the arm is not opening fully, one would think that the distance from the arm to the solenoid needs to be shorter to pull the arm open when the solenoid activates. This made the problem worse !!!!! The problem was the solenoid was not "latching" open. It would try to retract, but would not hold in the retract position. When I lengthened the adjustment to push the arm away from the solenoid, it allowed the solenoid to "latch" and hold the adjustment open. Very counter intuitive for this old boy.

The previous connection I had made with low voltage fit the failure mechanism. When the batteries were fully topped off, they had enough oomph to force the solenoid to latch. If they were down they could not force it to latch.

The symptoms exhibited were the generator would fire momentarily and then die or run at a very low RPM.

Maybe this will help you with a problem diagnosis in the future.

05-27-2008, 06:19 PM
Great information Richard. I will store that in my file of 'What the Heck Do I Do Now' information.

09-24-2009, 02:56 AM
I'd like to add something I learned about my yanmar generator. I think it will segue with Richards experience. My gen would crank but not start because the fuel solenoid was not opening even though it had 12V. I considered changing the solenoid but got choked up and immediately pursued other trouble shooting when I learned of the $260.00 price. I cleaned the electrical connections and replaced the electric relay that energizes the solenoid. Problem solved! I also learned that since the solenoid relies on an electromagnetic field acting on the plunger, the less extended it is when energized the more retracting torque it can exert and as Richard stated proper adjustment also allows it to "latch" into the fully retracted position.

Richard and Rhonda
09-24-2009, 07:13 PM
Where might the relay reside?

09-24-2009, 08:33 PM
Hi Richard,
On mine it is near the Start/Stop switch on the side of the engine. I was able to follow the wires from the F-solenoid over to the relay. It is a small black box approximately 1.25" square.