CIS Running Rough

[Paulporsche]

Check out posts 7 and 8 in this thread. Looks like the line to the lower part of the WUR on a 75-77 should be connected to the top port on the side of the throttle body. The top of the WUR connects to the lower port on the throttle body.


https://www.google.com/url?sa=i&url=http%3A%2F%2Fforums.pelicanparts.com%2Fporsche-911-technical-forum%2F336661-2-7-cis-wur-dizzy-vacuum-lines-routing.html&psig=AOvVaw272UdJnTbCcBI2iZxUyQCt&ust=1621127336945000&source=images&cd=vfe&ved=0CAIQjRxqFwoTCPiXw4rAyvACFQAAAAAdAAAAABAr

[kach22i]

Originally Posted by dfhtrhjn

Sounds like your WUR. I experienced the same behavior, exactly the same.

Okay, I'm going to have to switch my prior stance on this one because the original poster did a smoke test and it appears to be negative, so on to the WUR.

If he didn't have this problem prior to the WUR rebuild but has it now, working backwards the WUR would be the prime suspect as well.

ASIDE: On my neighbors MFI system air-leak last night I was able to help find the leak because I was a little more generous with the starting fluid (I brought the can after he ran out).

We tried using propane gas but could not get the same results, I think both our canisters were low on pressure.

EDIT:

What's up with all the dead-end links guys?

[DienstXIV]

Originally Posted by Paulporsche

Check out posts 7 and 8 in this thread. Looks like the line to the lower part of the WUR on a 75-77 should be connected to the top port on the side of the throttle body. The top of the WUR connects to the lower port on the throttle body.


https://www.google.com/url?sa=i&url=http%3A%2F%2Fforums.pelicanparts.com%2Fporsche-911-technical-forum%2F336661-2-7-cis-wur-dizzy-vacuum-lines-routing.html&psig=AOvVaw272UdJnTbCcBI2iZxUyQCt&ust=1621127336945000&source=images&cd=vfe&ved=0CAIQjRxqFwoTCPiXw4rAyvACFQAAAAAdAAAAABAr

Hi Paul, I have a 1975 car and my WUR only has one vacuum line port and it is on the top. From my research I am fairly sure that this is the correct WUR to have in my car. I have the vacuum line connecting to a T fitting that connects to the top of the Decel Valve and a small port at the bottom of the Throttle Body. I might try to connect the WUR to a T fitting that connects to the bottom of the Decel Valve and the throttle body because the vacuum lines seem to be about the same size as the vacuum port on my WUR. right now I had to put a reducer fitting in between the WUR and the T fitting going to the top of the Decel Valve. I am worried maybe the WUR isn't getting enough vacuum with that small vacuum line.

[DienstXIV]

Originally Posted by kach22i

Okay, I'm going to have to switch my prior stance on this one because the original poster did a smoke test and it appears to be negative, so on to the WUR.

If he didn't have this problem prior to the WUR rebuild but has it now, working backwards the WUR would be the prime suspect as well.

ASIDE: On my neighbors MFI system air-leak last night I was able to help find the leak because I was a little more generous with the starting fluid (I brought the can after he ran out).

We tried using propane gas but could not get the same results, I think both our canisters were low on pressure.

EDIT:

What's up with all the dead-end links guys?

Hi Kach22i, I did another smoke test this weekend and the only smoke I could find was coming out of the tape I used to seal off the top of the throttle body and the smoke tube. I also had some smoke coming out of the pop off valve but since the smoke is positive pressure and under normal driving conditions vacuum is negative pressure I think the pop off valve should be okay. I cleaned up the seal and when I would push slightly on the pop off valve cover no smoke would leak out of it.

My car has been running poorly ever since I bought it. It seems to run the same with the WUR vacuum line hooked up or not and with the electrical connection hooked up or not. I checked the voltage on the connection going to the WUR and it had roughly 12volts. Maybe I should check the cold start valve connection next?

I just got my fuel pressure tester kit and I plan to check the fuel pressures next. Maybe then it will help me figure out what is wrong.

One thing I never really thought much of is that while my engine has an issue with a steady idle. The actual RPM gauge seems to bounce around much more than and not in sync with what the engine is doing. Thought it might be the voltage regulator but the volts going to the battery stay steady when the car is running. I was thinking maybe this has to do something with my non adjusted points? I am supposed to get a Petronix pointless ignition system today, I'll put that on and see if that does anything.

Cheers,
Alex

[DienstXIV]

Originally Posted by Paulporsche

Alex,

John Walker recommends 3 - 3.5%. I would think this would be without a cat, which you wouldn't have on a stock 75

Try this for the PET:

https://www.porsche.com/international/accessoriesandservice/classic/genuineparts/originalpartscatalogue/

Click on 911, 1974-77

Hi Paul,

I checked the Porsche Technical specifications booklet for my year and model and it says between 2% to 2.5% I have a Gunson gas analyzer and it is really hard to get a good reading because the outside air is supposed to measure 2% but the reading is always changing, by a lot! I think I have it between 2% and 2.5% roughly, I will try to adjust it to run a little richer and see what that does. It seems like my engine runs rough either way. Sometimes I can adjust the idle screw and the mixture to get the engine to have a steady idle around 1000rpms but then I go drive it around and it won't run steady anymore. So frustrating! I am really starting to wonder why people say the CIS system is more reliable than carbs...

Cheers,
Alex:

[icarp]

A bouncing Tach is an indicator of a bad alternator or voltage regulator .
Ian

[DienstXIV]

Originally Posted by icarp

A bouncing Tach is an indicator of a bad alternator or voltage regulator .
Ian

Hi Ian, I have heard that as well but my battery is getting steady voltage, around 13.9volts at idle and 14.4volts at 2,000RPMs. My alternator light doesn't come on unless I lower the idle RPM to around 500RPMs in which case because I have an unsteady idle it kinda bounces between 1000RPMs and 0RPMs.

What is the best way to check the voltage regulator and alternator?

[agfours]

If you suspect fuel delivery, be sure to check fuel filter. I just posted about a clogged fuel (with pics), and I experienced poor idle, rough running, and the like. Easy to do, and as was pointed out to me by others, if you haven't done it within a year, it's overdue anyway.

[Paulporsche]

Are you sure the points are correctly adjusted? A bouncing tach can be a sign of bad or badly adjusted points.

Have you checked the number on the WUR against the charts I posted, and have you checked to see that your fuel and control pressures are in spec? After checking that all ignition parts are in spec, and verifying for no vac leaks, then getting the fuel pressures verified is the next step. You will need a fuel gauge with correct fittings for CIS to do this.

If you can't do this, at least get the people who redid your WUR to send you the fuel and control pressure numbers so you can compare them to the chart.

Have you tried Souk's field test for fuel setting w/o a meter? If you press up on your fuel metering flap just slightly while the engine is idling and the revs rise, you can go richer. A too lean mix can cause an irregular idle.

While you have the diz out to install the Pertronix, check the axial (up and down) play of the shaft. Too much play can reportedly cause an irregular idle.

[Dave Kost]

Check you ignition distributor for smooth movement? If the weights are stuck, you can experience erratic and intermittent idle and running issues.

Easy to check with a timing light and does cost you anything other than time.

[Paulporsche]

I have read somewhere that axial play in the shaft is not as critical when using a Pertronix as it is with points, although I can't verify this.

I recently had an irregular idle speed and, after running through the checks I mentioned above, I replaced my worn plugs and gapped them to .042 (with Pertronix) rather than the .028 spec for points equipped engines. I also replaced the O ring seals around the fuel injectors, and richened my mixture a little, and the idle is now rock steady.

[Dave Kost]

What is the timing set to?
How did you set it?

The timing advance should be smooth as the rpms increase.

When was the ignition distributor cleaned and lubed? You can pull it and dunk it in a gallon of penetrating oil for a couple of days and see all the crap come out.

When the timing is set, then go and set the CO and RPM to spec.

You probably have done this already.