Please lend an ear - Cold start analysis request - Link to mp3 included

[ZV8888]

Please lend an ear to this mp3 sound clip:

http://www.qms-software.com/ZV8888ColdStart.mp3

This is my cold start cycle. As you hear:

1. Starts fine
2. Stutters at about 250 rpm for 6 seconds or on very cold days it cuts out (<5C(40F))
3. Then warm up cycle continues normal

I want to get rid of step 2. Any Advice?

This is a 1979 911 SC with CIS. Warm fuel pressures are fine. Haven't checked them when the engine is cold - mainly because I don't know what the values should be. The Fuel accumulator is fine, fuel filter fine. Idle mixture set correct. I think the WUR is good as it was reconditioned last year. The Auxillary air thingy is open when cold. Cold start valve working.

Would love to get rid of the embarrassing 6 seconds what do the guru's think?

Thanks

[psalt]

I have found four things that affect this symptom over 20 years of seeing it. Vacuum leaks, ignition timing, spark plugs and mixture. Check for vacuum leaks at the injector sleeves with an unlit propane torch at idle. If you get an idle speed change, the injector sleeve O rings are baked. If you have the vacuum retard distributor, disconnect and plug the grey hose, rest the idle to 950 rpm, and see if it goes away the next day. If you do not have a vac retard distributor , set the timing at the high end of the spec. Use Bosch Normal plugs. On the +80 SC, it helps to set the closed loop mixture to 25-35 dwell, and the ******** super switch can help. On an earlier SC, if nothing else works, richen up the mixture slightly and try again. If you want to solve this problem, you need to make minor changes over several days, because you really only get one cold start a day.

[ossiblue]

In situations like yours, I'd advise checking the cold control pressure first, then proceed with options offered by Paul. You mentioned not checking it, but your symptoms are "classic" too high cold control pressure. You will need a spec chart for the pressures at different ambient temps--they have been posted here on different threads. Once you check/set the cold pressure, report back the results. If the problem is not fixed, follow advice given by Paul, one step at a time.

[ZV8888]

mmmmm, the ignition timing.... I did fiddle with that a while ago as I was getting lumpy running at about 2100 rpm. I retarded the timing a bit and that cured that particular problem. I can't honestly remember if I had the cold start problem at that time. It also seemed to help a slightly lean mixture on warm up. Ossieblue reckons it is a classic "Too high cold control pressure" so this would kinda make sense. I'll try and get a loan of the CIS pressure test kit again and check the cold control pressures. I have put on a new dizzy and have yet to change the plugs - but they are sitting on my shelf in the garage.

Thanks

[psalt]

All of the SC's I've seen with this symptom had spec fuel pressures. I'm sure others have different experiences with SC cold start stumbles.

[Paulporsche]

Here is the control pressure graph (middle one) for your car, in case you want to check them.