Timing 911s 2.7
 

My car has had some bucking issues. After some post and searching, it might be mixture/timing. I am going to test this weekend. I have read 101 and some of the other books but I am still not 100% sure of what to do.

First, is there a good affordable exhaust gas analyzer someone could recommend?

Second, can someone provide pictures or details on setting timing/dwell. I understand the timing concept using the light. Turn the distributor until you can the marks to line up. I have an MSD Ignition, does that matter?

Third, Dwell? I don't understand how you do this? Is the engine running? Is the distributor cap on or off? How do you check the dwell?

Have we tried a search? There must be a couple of hundred threads on these topics here.
:)

you may want to invest in CIS pressure gages first. even if your mixture is off, it could be due to wrong warm control presure and if you change the mixture, it will run bad when cold.

the LM2 is a good AFR tool.

MSD does not matter.

check your spec for timing. timing is usually set at 6k RPM, this also verifies the advance is working properly. i set mine while at idle, then check at 6K. it is easier than trying to set the timing while the RPM is that high plus you dont have to hold it up there. my timing is all in before 6k so i really dont have to go that high.

dwell? my opinion is not that critical. others i am sure will disagree. i just eyeball mine, as long as they are completely closed and they open enough to break the ground.

if it has not been done, the best thing you could is replace all the possible vacuum leaks. the rubber boots on the runners, injector O rings and sleeves, vacuum lines. this might just fix your problem. oh, tune up never hurts either.

Excellent advice from T77911s.
Dwell is just another more accurate way to check the points gap. As mentioned, it's not so important on a car with CDI like yours. On older cars with just points and a coil (no CDI) the points had to be open for as long as possible to allow time for the coil to build up a charge and get a good spark - especially at high RPM when there isn't a lot of time to build up a charge. With a CDI, the build up of charge happens very quickly, and the point gap isn't that important. The points only tell the CDI when to deliver the charge - not how much or how long.

The dwell is set with a dwell meter. The distributor has to be turning - at idle, at any RPM, using the starter motor with the ignition off, or with the distributor clamped in a vise using an electric drill to spin it. Whatever is best for you. The cap needs to come off for point gap adjustment. Some cars came with a little window cut in the cap, and you could adjust the points with the cap on, car running. I haven't seen any of these on a Porsche.

Just set the points with a feeler gauge and don't sweat the dwell - unless you like playing with and learning about ignition timing like some of us.