Fast Idle Speed Adjustment - Fan Clutch Free or Locked?

[Output Shaft]

Free?

 

[mattressking]

I've been thinking about this myself and I will throw out what I have experienced with mine.

I set my fast idle per the manual. At cold start, full choke and 6 pumps of accelerator (my carb needs work still) the motor kicks on and holds right around 1200rpms. When the fan turns off, the idle creeps up to 1800 where I set it.

To me that aligns with every other car I have owned in regard to cold start. Most hold for me around 1200 then drop off to idle, but those were all fuel-injected. I determined once fan is turning off, I close choke and drive off, keeping rpms under 2500 or so until the motor is warm.

Is yours going straight to 1800 with full choke?

 

[NeverGiveUpYota]

Interesting. Was just noting the slow creep up in rpms today on a cold full choke pull and wondered why. Totally starts w/ full choke at about 1200-1400 then it took ~3 mins to get to 1800-2000.

 

[mattressking]

Interesting. Was just noting the slow creep up in rpms today on a cold full choke pull and wondered why. Totally starts w/ full choke at about 1200-1400 then it took ~3 mins to get to 1800-2000.

That aligns with what mine does as well. To me it makes sense, on cold start you want engine speed to be high enough to circulate oil but not high enough to dissipate the lack of oil in the motor (think revving an engine high right when starting it, it's not good).

If fast idle was set at cold start and full choke, that means fast idle would be set with fan clutch on and put rpms at 1800 at cold start which to me is idling too high. If most manufacturers set cold start at 1200 roughly for all cars, then the functionality of the fast idle set at warm makes sense as the load of the fan brings it down.