Still Chasing Cold Start Problem
 

Installed a new WUR in my 81 SC, major improvment in cold running. It still really sputters on cold start though. Really pops and wants to backfire, but only for 10 seconds or so.

So where do I start. It runs great after that, but sounds lean at start up. I'm thinking cold start valve - any thoughts. It's pretty cold in my garage in December so I'd like to isolate this quickly rather than fish around. If it;s vacuum related how would I track it?

Thanks in advance

Jeff C
81 SC

What is the residual pressure when you begin one of these 'cold start' sessions? If it's not really low, then I'd suspect the cold start valve too. See if the CSV is getting voltage during startup.

Residual Pressure ?????? How would I know. Fuel pressure gauge left in place after coll down?


Jeff C
81 SC

Try this as a test. Turn your enrichment screw between the throttle body and fuel distributor about a quarter turn clockwise and start the engine. If it doesn't solve the problem, screw it back to its original position.

My 78 911 Sc does the same thing. It was running ok until I had to make it pass emmission inspection. So, in order to do this, I leaned it out a little. Now it does the same thing.

What I do now is turn the key to the start position and turn it off, wait a second and do it again. After about three tries it fires right up. I was going to turn the adjusting screw back out but it doesn't get that cold here so it's not a problem. Just a little more work for the starter but I don't use the car as a daily driver.

Steve

Jeff, I had the same problem on my 81SC. After putting in a new WUR, and setting up the CIS pressure gauge to see where the cold control pressure was, it was determined that the WUR was set too lean. You need to tap the plug in slightly to richen it up during cold start. You WILL need the pressure tester I talked about. If you need help, let me know. I spent alot of time and money trying to figure out my problem.

Thanks guys.


I'll order the fuel pressure guage today, and most likely be back with more questions next weekend.

Anyone selling a nice set of carbs with mainfolds?

Jeff C
81 SC

"Anyone selling a nice set of carbs with mainfolds?"

What, you must really like cold start problems!!!!

A few taps on my WUR, and my car starts like a champ at -15 F below.

Thanks to everyone for the help. Turned out I had two problems. The new WUR was working fine, the cold start valve is shot and I found a small vacuum leak.

The vacuum leak is fixed and after this post I'll order the cold start valve.

Thanks
Jeff C
81 SC

Jeff, where was your vacuum leak at?