Mysterious idle problem

[mulrik]

The problem is that the engine stalls on idle. This is what I have checked:
1) Timing is spot on.
2) Dwell is spot on.
3) Compression is good (~165).
4) I recently adjusted the CO to ~4% (at both pipes) with idle at 800 RPM
5) Valve clearance is spot on.
6) Fuel injection timing is spot on.
7) Injectors have been cleaned.
I have Bosch 7WD spark plugs gapped at 0,6 mm
9) When started from cold the CSV ensures an idle at around 1000 RPM, the CSV shuts of at ~50 degrees celcius.
10)I use a 15W/40 oil.
11) I have a new ignition coil, new breaker points and new spark plug leads.
12) Linkage is adjusted so that at idle the venturi is completely shut and IP adjustment arm is at top position.
13) The head has just been renovated completely.

When driven at 70 KM/H and above the car idles fine, but when I drive in the city the engine stalls (it is not so warm (10-15 degrees C) in Denmark yet so I believe that the engine actually cools at city traffic). However, when I idle after having driven at constant speed and turns on the heater the engine drops in RPM. This has led me to belive that the problem is temperature related. The CO level was adjusted with the car at idle for some time while adjusting (which increases engine temperature, unlike city driving where the "rolling" with engine at "idle" cools the engine).

I'm somewhat lost for ideas to solve this problem. Does anyone have an idea to address the problem??

Also, the idle adjustment screw an the back of the IP, does it affect the entire RPM range or just at idle??

Thanks for any input!!!
Ulrik

'67 250 SL Papyrus White 113043-10-000023

[Naj ✝︎]

I would check that the valve under the injection pump thermostat shuts the air off completely when the engine is fully warmed up.
To test, when warm , disconnect the rubber hose (air pipe to inlet manifold) from the fuel inj pump and block it with a bolt or a drill bit.
Then restart engine and see if its any better.

The fuel adjustment screw at the back of the pump controls only idling speed and upto 1700 rpm.

naj

65 230SL
68 280SL

[Malc]

Your coolant Thermostat operating correctly?
Malc

[ja17]

Hello Ulrik,
The injection pump knob adjusts low range mixture only up to 1700 rpm.

Joe Alexander
Blacklick, Ohio

[hands_aus]

Ulrick,
The inj pump thermostat will allow additional air and fuel to be used if the engine doesn't reach normal operating temperature.
The drop in engine speed could indicate a very rich running engine.
Have you noticed an increase in your fuel consumption?
Have you checked your spark plugs since running the car in traffic?

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto