Thank you for your thoughts.
Yes, the engine when cold fires with very little cranking, meaning 1-2 seconds. It seems to me the Aux Air Valve, or CSV?, is working properly, but can be easily tested as the CISprimer says it closes as soon as there is 5-6 inches of vacuum, which would be quick.

As for the Auxillary Air Regulator, does someone have a chart which illustrates the relationship of the AAR, ambient air temperature, engine temperature, and when it closes?
I assume this is the device that drops the cold idle from 2,000 rpm to 1,100 or near,13-14 seconds after cold start, which seems like an awfully quick to drop to a normal idle rpm range?

Background on engine - has about 2,200 miles on it rebuilt by a well known Houston area fellow named Peter Baldauf and the machine worked farmed out by Peter to a San Antonio specialist, Jones Autowerks. In January of this year, Peter serviced the engine including setting the valve gaps. The reputations of both of these shops is impeccable thus I’ll assume the engine is very healthy.
Nevertheless, when diagnosing something amiss in how an engine runs, one always runs down a basic checklist which I will:
Check the spark plugs
Check the timing
Inspect the vacuum lines, testing where able, such as inserting a hand vacuum pump and testing devices for movement and that they hold a vacuum. (Note, previous owner installed VDO vacuum gauge in the console, very neat!)
Overall visual inspection of induction rubber pieces and seals lookin for leaks.

1) As far as digging deeper into the operation of the CIS, I’d like to know an answer to the above question regarding the CSV.
2) I’ll run a fuel pressure test - books and the CISPrimer website state the cold fuel pressure by the Control Pressure Regulator, WUR, should be 1.6 bar at 10C and 3.4 bar at 40, but once again, there is no chart of what happens in between these ranges? Am I to assume that if it is 1.6 when 10C and increases to 3.4 bar when device reaches 40C that it is functioning properly?

That’s enough for now. Thank you for your help.

Thanks, Mark. I did find a chart in the Bentley Service Manual that relects the fuel pressure basically moves higher at a linear rate until in maxes out around 40C.



So this afternoon,64F (17C) in the garage, I hooked up test pressure gauge per the instructions, pulling the fuel pump relay, jumping terminals 30 to 87a, disconnected electrical connection at WUR, turned on ignition, had a closed fuel line gauge.
This gave me a system pressure of 5 bar, which is in range.
Next, I opened the valve to include the WUR and the pressure didn’t change, still 5 bar.

I tried multiple times and had same results.

I started the engine and pressure dropped to 3.4 bar which is range for a warm engine, and of course, my engine was coughing and popping back through the pop off valve.

So, I think my WUR is not working properly, so I removed it and took it apart. I measured the resistance of the heating element and it was 20 ohms, which upon disassembly shows it is labeled 20 ohms, so it should be good. ’ll order a rebuild kit.