1973.5 cold start

[tkrefeld]

My 1973.5 CIS 911 runs great but has a hard time starting..I have a working lever between the seats but it is stll hard to start winter and summer.....I have been told all CIS cars have a cold start valve but have also been told the 73.5 does not. Any ideas?

[Jubbie]

The lever between your seat should raise the idle speed. It just connects to the throttle linkage and pulls it just like pressing on the gas does. You may want to check and see if it still works since there is a plastic part that connects to the linkage that rots to dust with age.

Later on (I think 75' or 76') the leaver between the seats was replaced with the Aux Air Valve (AAV) and Aux Air Regulator (AAR) which bump up the idle by bypassing air around the throttle butterfly. The AAR closes with time as an electrically heated element or car heat heats a spring. You should not have an AAV or a AAR in your 73.5'.

You do have a cold start valve which is a fuel injector into the CIS airbox that is triggered when the starter is engaged and the engine is cold based on a temperature sensor on the drivers side timing chain cover.

Also the Warm Up Regulator (WUR) which all CIS cars have adjust fuel/air mixture with respect to altitude, temperature, engine load (in some cases), and engine temperature.

If the throttle lever works, I would get some good books, tools, or a good mechanic to check out the WUR setting and the cold start valve operation.

There was a great web page on 911 CIS, but I have lost it.

[Early_S_Man]

Device #12 in the 73.5 schematic below [from the Pelican Electrical Diagrams page] is the cold-start solenoid ... it is connected to the Yellow #50 starter solenoid lead.

[buster73]

73.5 CIS do have a cold start enrichment valve which injects additional fuel into the manifold when the engine is cold. They also have a control pressure regulator (warm running compensation) which keeps the mixture rich during warm up.

74 and later models have an additional thermoswitch and a microswitch connected to the hand throttle. This setup just prevents the cold start enrichment valve to inject fuel into a hot engine by accident. The postition of the cold start enrichment valve has also been moved to the center

73.5 CIS start enrichment valve and Control Pressure Regulator



74 CIS Thermoswitch (left chain housing cover)

[Paulporsche]

If your engine starts then probably your cold start valve is OK.

If your levers raise the idle speed but the engine still backfires during warmup then your WUR is probably out of spec, giving the wrong control pressures, and subsequently the wrong mixture.

Search WUR and also jim williams who has a site w/ lots of valuable info on the CIS.

By the way, the Control Pressure Regulator and the Warmup Regulator are the same thing.

[LakeCleElum]

I had that problem recently with my 73.5.....Make sure you're pulling the lever ALL THE WAY UP to trigger the WUR. If the WUR is bad, they're about $400 for the part and adapter. The bill to replace mine was over $800, with labor and new plugs....I'm learning and now do my own work.....

[Paulporsche]

Lots of posters have cleaned and/or adjusted their WURs themselves to get them to run correctly. You can check the control pressures w/ a fuel gauge to verify the settings.

[HarryD]

Check to be sure that the control wires are connected to the cold start valve. I accidentally unplugged mine and it was a bear to get the car to start. Once I plugged it back in, it started 9and contiues to start) just fine.

The unit in located (as you look into the engine compartment), facing the passenger compartment, on the left side, and in the Throttle body. You can see some pictures here: Start-up Injector Fuel line leak