D6-9U - Governor adjustment ; idle setting

That sweet spot shouldn't have much of anything to do with the high idle and certainly nothing to do with the low idle.

I would guess that the rack setting is the ultimate limit on fuel delivery and power output, so you won't change that by changing the high idle rpm, but you may make it run hot(ter) since in most applications the governor won't stay on the torque spring (max fuel) very much of the time, so when it's not working quite that hard, the high idle rpm (which translates to about 10% lower loaded rpm) sets the fuel delivered and heat produced under normal work.

An easy tach to use is a photo tach that uses a reflective sticker on the crankshaft pulley or the U-joint behind the clutch to bounce it's light off and count rpm's.

Low idle should not cause the engine to die. You should have to push the throttle control fairly hard to make it flip the idle stop over so the governor goes to cutoff.

The rack setting has not been altered during my work. However, I feel that you may have hit on my problem, sounds like I need to get the rack setting right.
Remember reading about the measurement a time or two so I will brush up on it and research some.

Curious though, how would the rack setting become 'out of whack'? Would or could it simply be a factor of time, or just wear and tear? Cause' eye know that this ole' girl has not had much attention since way before I got her coupla' years ago. (She was being push started regular on a farm, till the guy I got her from got the pony going)

thanks for the comments and ideas, sure will help me get this worked out!

The gov rack travel won,t move unless someone has played around with it and then you,ll need the rack setting gauge to re-adjust it. It is a bolt with a jam nut on it so it won,t change unless someone changes it. If you are experiencing low HP or in other words it won,t hang on a push or a pull then it usually is a Gov. spring that,s lost tension. Some guys claim they adjust it by turning it on the factory end adjustment but you don,t have a way of knowing how much to adjust it.o your only guessing so a new spring is the best and only way to go properly and I found the 5F6413 the best spring that the rack setting book calls for with a .215 rack setting.Also with a 5F1941 it calls for a .125 rack setting.I found over the years those big Cat V8s and V12s would work best with that 5F6413 spring.You might want to check the gov. spring # in it now and get that one so the rack is set for that spring.