Idle Increases at warm up- 73.5 CIS injection

[67softwindow]

Hi Folks,
I just pulled my 73.5 out of long term storage and got it started again. It has the early CIS fuel injection Starts easily and idles nicely but the idle soon begins to climb and climb until it is clearly too fast at which point I shut it down.
I know it has a warm up pressure regulator which is supposed to lean the mixture during warm up but the idle behavior seems odd.
By the way it ran well when parked 10 years ago....

Any thoughts are welcome and appreciated.

Thank you
Dan

[gled49]

Not a fuel system that tolerates non use. After fresh fuel you should have a qualified tune and fuel system check and adjust. Fuel system also likes seasonal adjustments. Gordon

[edmayo]

And,,,,make sure the hand throttle is off

[Jsottile]

Hi Dan,

Early CIS is fairly robust and straight forward to check. Based on what you wrote, my first guess would be a leaking cold start valve (CSV). When cold, the engine welcomes the additional fuel. As it warms up the additional fuel may cause higher RPM. First, remove the fuel feeder line for the CSV from the back of the FD. Next, pull the electrical lead from the CSV. Finally, there are 2, 4mm allens that secure the CSV. Buy a cheap 4 mm T- handle allen and cut it down to 3.5in long. It will fit nicely at the back of the air box. There is an O-Ring that makes the seal. Make sure that comes with it. You can bench test the CSV with a bit of fuel and regulated air at 40psi. If it leaks, replace it. Not that easy or cheap to find. This should take an hour if it’s your first try. I would also energize it with 12v to make sure the solenoid is working. You will hear it click.

For checking the WUR, first I would check the resistance to make sure the bi-metal spring is good. It should be 15-20 ohms. This is from memory so you may want to check. If good, the only other way to check for sure is to buy a pressure gauge. If you have CIS, you should have one of these. You can check the cold pressure and start the car and watch the gauge. It should go up. You can look up the exact numbers.

After sitting 10 yrs it could be a few other items as well. The o-rings around the metering slits on the FD barrel can deteriorate and leak. Fuel injectors get weak and leak. If all is original, 43 years then ??? could be many things. But the two above items are a good place to start and something you can do on a Saturday afternoon.

PM me if you decide to tackle this project or post. FYI- you can remove the entire CIS-airbox all in one shot by removing 13 nuts, 2 on each intake runner and one support.

Good luck. Let us know what you find.

[ESully]

After sitting such a long time a full tune up needs to be done, including system pressure and control pressures.
The WUR and Throttle position switch on the 1973 CIS control mixture, but not the idle speed. Warm idle needs to be adjusted on the throttle body, and hand throttle is adjusted by setting the collar on the throttle rod in the center tunnel to about 3,500 rpm max.
1973 CIS starting procedure is with the hand throttle raised, and lowered as the engine warms up. It is different than later ones since it has no thermal time switch to control the cold start valve. Cold start valve is activated when the hand throttle is raised, closing micro switch on throttle body, and key is turned to start position.
This thread on Pelican goes through all the adjustments of the linkage.
http://forums.pelicanparts.com/porsc...tle-lever.html
And this is the start procedure from my manual.