timing

I have a 1976 911S 2.7L CIS. The static timing for my car is supposed to be 5°ATDC at 850/950RPM. I went to time the car, and the car was set at TDC and idling at 900RPM. When I moved the distributor to 5°ATDC the engine idle dropped to 400RPM. I took the car for a drive after I set the timing and it seemed less powerfull than when I started. Is it normal for the engine idle to drop when the timing is adjusted. Now that the timing is correct should I go back and bring the idle speed back up to 900RPM or am I doing something wrong. Also, what is the procedure to adjust the idle on a CIS engine.

My .02 from my experience with my '73 2.7 CIS.

It depends on how you want your car to run. Do you want it to pass smog? have you modifed the car? Changed cam?

The best way, that I have found to set timing involves a vacuum gauge, timing light and a propane bottle with a pressure reading and some tubing.

Now Assuming your distributor is set for your engine and is functioning properly (i.e. advancing correctly), then setting initial timing is pretty easy and should work for your full advance timing. Generally speaking, I have found the best power/performance is setting the timing where the vacuum is at the most (vacumm gauge). Then retarding the timing a few degrees, better torque. Of course doing this may give you higher RPM pinging.

Now you get to set CO, then set ignition, then set CO again. Setting CO uses the vacuum gauge and the Propane. When putting the propane into the intake and RPMs increase, your most likely running a little too lean.

After I did this my '73 was doing 0-60 in 5.3
Although it pinged in the 5 -6K rpm range. That was OK for when I just drove around town.

Good luck!
Nick

I have not made any major performance modifications. I am unable to go to a more aggresive CAM with the CIS system. The smog blower is removed and I have replaced exhaust system with a 1974 Style and installed a sport pipe. Basically the engine idles rough and misses at higher RPMs. These are not really drastic problems, but the engine does not seem smooth to me. When I put my hand in front of the exhaust, there are "sputters" for better choice of a word. It does not seem continuous and smooth flow. I also get an occasional backfire. I had posted earlier on this board regarding an MSD or Permatune ignition system upgrade but was convinced otherwise. I have installed a new distributor cap/rotor and new plugs. I did not replace the wires. Should the engine idle drop because I adjusted the timing. I'm not looking to time the engine for racing, I just want it to run smooth and be properly timed. If I can eliminate the timing and ignition as the cause, I will start to look in other places for the problems that I am having.

For what it's worth, I have heard of people putting the SC cams in the 2.7's. It supposedly changes the power curve a little so the motor feels like it has more power throughout the RPM range. I do know that WebCam Inc sells a modified cam for the 2.7 CIS motor.

Mark
'74 911S Coupe

Anytime you retard timing the rpms will go down as you experienced, that's why there's a volumn control screw on the left side of the throttle body so you can let in more air to compensate.

Your rough idle is probably due to a poor spray pattern on one or more injectors.

Cheers,

Joe Garcia

[This message has been edited by stlrj (edited 03-19-2000).]

Agreed. Advancing timing virtually always will increase idle speed. But that's not just always good. Over-advanced timing (pinging) can kill motors, and I assume that's just as true with Porsches.

You report sputtering, backfirng and cutting out at hight RPM. This sounds like ignition trouble. Maybe. You're on the right track though. Eliminate ignition then look at fuel/air. Good luck.

Have you checked all of your ignition wires with an Ohmmeter? If you don't get an end-to-end measurement of 3000-5000 Ohms, check the Beru connector ... they sometimes will be open because the internal resistor is broken. The CDI can jump across the gap at idle (until the plug is fouled) but will miss under load at higher rpms. Sometimes the black neoprene wire breaks down, too, at higher rpms. All of the sparkplug wire connectors 'unscrew' ... and the wires can be replaced with bulk silicone 7 mm wire, cut to the same length. I recommend AC-Delco wire ... it is orange, and has stainless steel core wire. You can buy it by the foot at a well-stocked parts store handling AC-Delco line.

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Warren Hall
1973 911S Targa

Thank you for all the help. I removed the ignition wires and all of the resistance readings were within the range 3K-5K that Warren had mentioned. The car is now timed at 5°ATDC and I brought the engine idle up to 900RPM. The engine has not backfired yet and seems to be missing less at higher RPMS. There is some improvement, but it is still not as "smooth" as I would like. I think that I will remove the fuel injectors to check the spray pattern. Does anyone have any other recommendations for items to be checked? Where else should I be looking to cure the symptoms that I am having?