1970 280SL Idle question

[Mullera]

Actually 2 questions.  Motor completely rebuilt well
1. Car starts and ldles perfectly.   Starts at 1000 rpm . During warm up idle goes down to 750 rpm at exactly 180 degrees.  Put in gear idle goes down to about 550 rpm.  Vacuum dashpot on Venturi does not work and I think it’s just the good condition of the motor that I do not stall out . Next , on a drive , temp needle rests on top of the 180 degree hash mark , . Change to neutral and idle is 1000 rpm again ,not 750
As during start up .  Just will not come down to 750. Don’t mind too much as it is just an idle issue but it should work correctly.   Any ideas why it goes up to 1000 and will not come off ?
2 . Can one fix  a  vacuum dashpot as above    ?     All the the tolerances are correct .
Thanks
Allan

[Cees Klumper]

Have you checked whether any of the linkages are maybe not totally free, meaning something is preventing the idle from going back to 750 rpm after everything heats up really well? With the engine idling at 1,000, can you get it to go back to 750 by pushing the linkage back to the stop by hand?

[ja17]

Make sure that the mechanical advance mechanism and the vacuum retard mechanism in the ignition distributor are working correctly. You can get an inconsistent idle if these are stuck or defective and not working correctly.

[Mullera]

Thanks for your advices.
I will check both and report back .
Next to snowing here now so will take a few days !

[Berggreen]

Hi Allan

After checking the linkage and ignition advance, also check the linkage solenoid, which pushes on the linkage, when you move from Park or Neutral into gear.

Ideally, it should, after warm-up with warm engine, idle in Park/Neutral at 750-800 rpm at around 4%CO, and when you then move into gear the linkage solenoid should be adjusted, so that it compensate for “loss” of rpms and prevent the engine from stalling by pushing on the linkage to increase rpms back to 750-800 rpm.

You adjust the solenoid by increasing/decreasing the length of the pin pushing on the linkage.

Cheers,

Christian