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Discussion Starter #1
According to the instructions, my JD should run at 2700 rpms under load, ie when the PTO is being used. According to the dash, it doesn't; it runs about 2500 rpms when the foot throttle is completely depressed.

Should I worry? And if I should, how would one go about adjusting the throttle on this tractor. It's diesel, and it doesn't seem to have a carburetor with easy idle adjustments.
 

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First of all, there is no reason to worry if tractor is performing to your satisfaction. Sometimes the tachometers are not very accurate and it may be actually running fast enough. What pto equipment are you running? Some implements work fine at lower speeds and some are not very efficient at lower speeds. Does engine speed stay the same if you use hand throttle? Look at the linkage that goes to the injection pump. You will see it moving on right side of engine when you push foot or hand throttle. If you hold throttle in fast position, look at the lever on injection pump. There is a stop screw there that limits how far the lever on side of the pump can move. If it is not contacting the stop screw, then you can shorten the link from foot throttle to injection pump until lever contacts it at full throttle. If lever on pump is already contacting the stop screw, then you can back off the screw, but I would want to verify that engine speed is actually too slow first with a photo tach so you are sure you aren't overspeeding. Those stop screws don't typically need adjustment.
 

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Discussion Starter #3 (Edited)
Couple of relevant things. The bolt that holds the throttle assembly together at the ignition pump end has fallen off twice. I don't know if that is the "stop screw" that you are talking about. I had no idea what I was doing, so I just screwed a new bolt on it each time. Didn't think about the bolt falling off affecting the idle. I was worried later about the idle, so I messed with the bolt. Now the tractor runs close to 150 rpms higher (per the dash tach) if the hand throttle is used. With the hand throttle, it shows as running within the "PTO range," but not at 3500 rpms. If I'm remembering correctly, it's showing about 2700 rpms. With the foot throttle, it doesn't show as running within the "PTO Range".

I must also mention that the injector pump has been rebuilt, and it was after that the bolts started falling off.

I mostly use the PTO for a brush cutter that has always been at the top end of what this tractor can handle. I needed a new PTO shaft on the cutter, and John Deere installed one that seems to me to be MUCH heavier than the original. If I am remembering correctly, it was after the new shaft that the ignition pump went bad. I have no idea if the two things were related.
 

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Item 38 in first diagram is the throttle lever on the pump. #36 is the stop screw to adjust speed. Second diagram shows the rod that connects to the lever. You can adjust the length of rod 22 by turning nuts 25. WHich bolt are you having problem with coming loose?
throttle 870.PNG

870 throttle.PNG


The pto shaft on the mower wouldn't have any effect on injection pump failure. Unless something is out of balance and causing extreme vibrations.
 

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Discussion Starter #5
It was #25. I'm not sure if that diagram isn't sort of upside down, but on my tractor, the inside nut is snugged up about three threads from #24, and the outside nut is almost at the end.

It was the outside nut that fell off twice and the whole lever came apart, so I put a lock nut on it. I was only able to make it home at the transmission gear speed.
 
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