Question: Mixing CIS Parts, different years.

[Tidybuoy]

I acquired my car from a reputable Porsche mechanic. He was president of our local PCA, owned his own shop, and eventually left town and went to work for Canepa Design.

My question relates to the Fuel Distributor and WUR. As seen below, he used a '76 WUR and a '79 FD. If I need a new fuel distributor, should I be looking for a '79. And, I thought the '79 was for a 3.0.

My '74 came with a rebuilt 2.7 with the following specs: (per his literature)

[stlrj]

How does it run? Are you having any issues?

[manbridge 74]

Can you get in touch with the PO and see his reasoning for the larger FD? Perhaps it was to go along with extra engine mods.

In any case a wide band 02 sensor could help you see A/F ratios to determine if you are over/under fueled.

[Tidybuoy]

Originally Posted by stlrj

How does it run? Are you having any issues?

I wasn't until recently. The car is running rough and although the fuel pressures are in spec, the injectors are pulsing at low volume. I was suspecting the fuel distributor since I recently had it off to replace the o-ring and paint. And since I saw a '79 FD for sale I just thought I would ask. When I had the fuel distributor removed, the piston was initially moving freely and slowly. But I let it sit (in a Ziploc bag) and the piston froze up. I got this moving again with soaking but I've been concerned I goofed something up.

I just purchased new injectors and I also ordered the fuel pressure regulator kit and I'm hoping that this helps. The biggest issue is idle and low rpm cruising. When looking at how the injectors are spraying, I know something is not right and it's looking like fuel delivery issues (way too much at low rpm and no atomization).

[stlrj]

Originally Posted by Tidybuoy

The biggest issue is idle and low rpm cruising. When looking at how the injectors are spraying, I know something is not right and it's looking like fuel delivery issues (way too much at low rpm and no atomization).

You might need new injectors. That alone might be your problem.

[Tidybuoy]

Originally Posted by stlrj

You might need new injectors. That alone might be your problem.

I will find out tonight - my injectors came today. Leave it to Pelican to deliver within 24 hours...I don't know how they do it.

[boyt911sc]

Vern,

I saw the video of your fuel injectors' test and my first reaction was that I had thrown away some CIS injectors that have better spray patterns that your three injectors. Wait till you see the new injectors spray v-shape uniform mist pattern. What you also need to know is at what 'operating pressure' the old injector/s were opening. And one injector in the video did not close properly as you could see the drippings. If these fuel injectors are representative of the other three injectors (not shown in the video), don't expect to have a smooth running engine. You need six (6) good operating fuel injectors. Keep us posted.

Tony

[javadog]

I don't think I would mix a mass airflow unit from a '74 with a fuel distributor from 1979. There were also significant differences in the WUR cold control pressure graphs between 1974 and 1976 and so I'd be tempted to go back to 1974 components for both the WUR and FD. Nothing Porsche did after 1974 was for more power, until they built a bigger motor...

Need a tech spec book for a '74?

JR

[john walker's workshop]

pulsing eh? take the air filter off and see if the sensor plate arm is pulsating at idle. it's a FD issue if it is.

[thumbdoctor]

I have a mix 'n matched CIS, 1977 911 S with 79 FD, 79 airbox and tubes matched to the inlet ports. 075 WUR (made it adjustable). It took a while to set up but now it works well. Had some issues with the injectors singing when the fuel pump was energized. Took off the FD and polished the plunger with 2500 wet or dry and then on a cotton wheel. Also polished the vane roller and fulcrum. That settled the injector woes, starts well and idles at 1000 warm, no surging and pulls throughout the RPM.

[E Sully]

I would be wary of using an early air metering plate with a later fuel distributor. The shape of the venturi is carefully calibrated to the movement of the plunger for proper fuel delivery. Like the wur, it's taper varies to control the movement of the plate for the fuel distributor to deliver the right amount of fuel. Also, the total flow for the 2.7l was 850 ml in 30 seconds, later SC was 1000 ml. I don't know the specifications, but I would think the later SC fuel distributor would have an overall greater fuel flow for the larger displacement.
Later WUR should work as long as vacuum lines are properly hooked up and throttle position valve was removed.
It may be able to be tuned correctly. You would need to be able to check afr. First thing I would say is to make sure the air plate is set at the correct starting height, upper part of the plate flush with the bottom of the taper. It needs to be set with no pressure in the system. Also check to make sure the piston moves freely at that point.