Although I don't have a diesel tach or tachntime, I know what 750 RPM idle feels like and my LD28 idle is more like 1200 RPM. In fact, the idle speed has been speeding up over the past several months.
Went to adjust the idle as per the FSM procedure, moved the stop screw about a 1/3 turn out, no effect. Throttle cables all have a bit of slack. Does the adjustment screw need to be turned a lot for noticeable idle RPM change? What would cause the idle speed to slowly creep up? Is the engine just now getting broken in (247K mi.)? Or losing compression?
How about a failed Cold Start Device (CSD)? Think of it as fast idle. Mine's never worked, I think it is stuck "up" and was adjusted to be non-functional years before I got it.
In the pic below, the CSD is the part on the left with the black bellows on the stem. It both props the idle andraises the base RPM timing advance.
If the CSD is stuck "up", the screw up near the cable is non-functional for a lot of its travel.
For others reading this: the CSD above is the 1981-82 style. The 1983 style is different, and is mounted lower, horizontally, and is slightly smaller.
Or losing compression?
