Hot lean running issue

[jedwards]

I have a early 1967 250SL Auto and I seek the help of our  forums to unravel a problem I don’t seem to be able to get on top of.

My car starts perfectly from cold. It warms up nicely and soon reaches its normal operating temperature and runs beautifully. New radiator, new 89 degree thermostat,  running exactly at specified temperature.
If I drive the car for say 30 minutes, at the beginning and end of a day, and allow it to cool during the day, then it behaves perfectly.

However, if I drive it again within a few hours, say in the middle of the day, the engine heat seems to soak in fully and the motor starts to run lean, resulting in rough in-gear idle and slight loss of power under load.

So I clearly have a lean hot  running problem,  but I have double checked the WRD and it is definitely off the rack and fully closed at operating temperatures so I am reasonably sure that this is not a matter of WRD adjustment.

What else in the enrichment system is specifically impacted on by full engine temperature that is not effected by a warm motor?

[nahuston]

You may have a vacuum leak somewhere that is not noticeable when the engine is warming up and getting more fuel from the enrichment devices but shows itself when the extra fuel is shut off. Also check all of your linkages and the setting of your venturi/ throttle plate. They may be out of adjustment creating the same condition. 

[ctaylor738]

If you are sure it's a lean condition that's causing this, why don't you fatten up the idle mix a couple of clicks and see if that helps?

Cheers,

CT