cold start issues - 911 SC
 

Just finished rebuild on 3.0. Has 964 cams and By-pass pipe/GHL muffler. On cold start, does not seem to idle up - idles around 950 - and sputters/occassionally pops through air box. Have to wait a few minutes to drive off, and even then it doesn't run well until warm. Also seems to be low on power until fully warm. After warm up starts and runs OK. Passed emmission test easily, with very low CO, etc. From reading the archives, my thoughts are: 1. it is very lean and richening the mixture may solve the problem (?) 2. there is a problem with the WUR (I looked at mine-1981- though I haven't looked real hard yet- and don't see the plug that people talk of punching to enrichen at start up- do you have to unhook one of the lines to do this?)3. there is a problem with the Aux Air Valve. I'm taking it to a porsche only shop with the gas analyzer equip. in a few weeks, and am hoping that a simple adjustment to the mixture may do the trick, but what do you guys think?

You need to conduct a fuel pressure test first.

I had a similar problem with my old SC and it turned out to be a vacum leak.

I have a 79SC with the same problem. Over night or left for hours it will start sputter and die, restarts just fine and runs great its just that first start. Anyone got a road map to the vacuum lines?

JBO: Because of the 964 cams, did you change the timing? Is it still 5deg BTDC? Setting the mixture is easily done. If that does not help, before you do anything, check the fuel pressure cold and warm. On cold start, a whole sequence from Thermo-time switch, to Cold Start Valve, AAV, AAR, WUR, takes place. The Bentley has a good description 200-5/7 and 240-20/21. I had some small vacuum leaks after a rebuild.

Thanks guys. I did look for vacuum leaks and everything seems OK. I'm heading out of town for 10 days and think I'll just take it in when I get back since I don't have the tools (or probably the skills!) to go any farther myself.