Idle issues

[Isait]

Hey guys my 1984 Datsun 720 doesn’t idle unless the clutch is engaged. Does anyone know why? I’ve messed with timing but not much as well with carb(hitachi). Like I said the car idles fine when clutch is pushed in but as soon as released it stalls

[datzenmike]

Engaged would be with the pedal up and the pressure plate gripping the clutch disc. There is a switch on the clutch pedal. Unscrew the switch and tie up out of the way, see if that fixes the idle problem.

 

 

[Isait]

I just unplugged the switch and now the car does not need the clutch to be engaged to idle. Thanks can i get the name of the part so I can replace?

 

[datzenmike]

The switch obviously works so leave it. It's not hurting anything by leaving unplugged.

 

The 720 has a fuel cut system. Under deceleration the carburetor closes to the idle position so even though not needed for idling the gas is being sucked through the engine and out the tail pipe and wasted. As all fuel to the idle circuit has to pass through the idle cut solenoid it can be turned off under certain conditions of high manifold vacuum. To prevent the engine stalling if you put the clutch in or if you were to coast down hill with the transmission in neutral and the clutch up there is a switch in both that over rides and restores the idle cut solenoid and allows idle. I'm no expert on how exactly this works, my guess is the neutral switch in the transmission isn't connected or unplugged. I'm assuming you are in neutral when you let the clutch up and it quits?

[Isait]

So the car was idling perfectly yesterday in neutral. However today the car isn’t idling unless applying gas. I know the carb and timing is fine bc when the switch is plugged back in the car idles fine with the clutch engaged. So should I continue to adjust timing/carb or replace the switch? 

[Stoffregen Motorsports]

Have you checked for power at the idle cut solenoid? Check the connection and the wire for cracks, abrasion or corrosion.

[datzenmike]

17 hours ago, Isait said:

So the car was idling perfectly yesterday in neutral. However today the car isn’t idling unless applying gas. I know the carb and timing is fine bc when the switch is plugged back in the car idles fine with the clutch engaged. So should I continue to adjust timing/carb or replace the switch? 

 

Got to ask yourself what is the difference between the switch with the pedal down or disconnected??? well the short answer is .... no difference. The switch is either on or off. 

[Isait]

Good point thanks for your help