YES there is something inside your injection pump which can stick which will give the symptoms that you're describing. It's essentially the fuel adjustment pin which slides in and out as you adjust your throttle. As you increase your throttle, the pin slides out into the boost diaphragm hole which, according to the given amount of boost, gives your engine more fuel. If you look at the top of your pump, you'll see the boost diaphragm housing. The top cover (to which the boost diaphragm pipe connects) is fastened down with four very tight flat head bolts. Remove these four bolts (it may require some effort) and then remove the diaphragm housing lid taking care not to bend or kink the boost pipe. Once the lid is removed you will be faced with your boost diaphragm. Mark it's original position (although this is not entirely important) and then rotate it a full 360 degrees. Doing this will push the fuel adjustment pin back into its housing and you should then be able to lift the boost diaphragm out of the housing. Take care not to loose the nylon washer or the resisting spring. Now look down the hole. Towards the front of the engine (or to the right if you're looking at it from the drivers side) the fuel adjustment pin will be sitting in its recess. Manually adjust the throttle lever so that it is at it's highest setting (full throttle) and the pin should move out of the housing and into the recess. It may move out quickly or it may move out slowly. If the pin does not move out at all, start the engine without re-fitting any of the parts that you have just removed. Give the engine full revs for about five seconds (it might be accompanied by lots of black smoke from the exhaust) and then shut it down and look into the hole again. Has the fuel pin moved right out into the hole? If so, spray it with penetrating oil or WD40 and then push it back into the recess towards the front of the engine with a small screw driver or the like. Manually give it full throttle again with the engine off and the pin should fly straight back out and almost tough the other side of the hole. Spray again and repeat it as many times as you like until you are sure the pin is 'free'. It's possible (as was my case) that the pin may stick every now and again, making the engine seem un-responsive. suddenly it will free up and away you go.
If the pin does not slide out of the recess you'll need to remove the throttle arm from the splined shaft on top of the injection pump. This is held on with a single nut. Remove the nut and then carefully un-hook the return spring so that you can lift the throttle arm off the spindle. Take care not to adjust the position of the spindle once the throttle arm is removed because it'll adjust your engine idle speed. Once the throttle arm is removed, you should be able to see a grub screw mounted horizontally which can be removed to give access to the front side of the fuel adjustment pin. Remove the grub screw and then use a tool to push the adjustment pin into the diaphragm housing. Spray the whole assembly liberally with a good penetrating oil and then lubricate it with diesel, pushing the pin in both directions ten to fifteen times to free it up.
Re-assemble all parts removed, including the boost diaphragm, nylon washer, spring and lid and then take it for a ride and see how it goes. If you want me to clear anything up for you or describe it in further detail send me a private message with your number and I'll call you.
-Pos
I'm trying to figure out what drives the fuel adjustment (stroke limiting) pin from the photos of the top cover.
