Ignition Timing 1968 911L 2.0l

[gduplock]

Car has standard 2.0l engine running Weber carburettors, Bosch distributor with no vacuum advance.
I have been struggling for some time to get the engine running above 4000rpm, it's fine at lower revs apart from occassional popping on overrun. Played with timing and points gap and renewed ignition sevice parts to no avail.
User manual states plug gap 16 thou, dwell time 38 +/- 3 deg and static timing 0 deg BTDC. I've not been able to check dynamic timing at 6000 rpm, manual says 30 deg BTDC.

Yesterday as last resort set static timing around 10 deg BTDC (when measured accurately was in fact 8.5 deg). She now runs well up to red line (6300-6600 rpm) :bounce: :bounce: . There is still occasional popping on overrun.

Would you consider this normal operation or is there likely to be problem with worn distributor components? :?: :?:

I am planning to check dynamic advance up to 6000 rpm.

Your thoughts appreciated.

Graham

1968 911L 2.0l Sportomatic

[chris_seven]

Graham,

You really need to check the dynamic operation.

At idle 850-950 rpm the timing should be at about 3 degrees After TDC and at 6000rpm should be 32 degrees (+/- 2 degrees) Before TDC.

If you have the Static Timing at 10 degrees Before TDC you are in theory over advanced as this would give timing at idle speed of up to 20 degrees.

Timing at 6000 rpm would probably be limited by the stop in the dizzy.


Do you have the Bosch Part Number of the dizzy?

If you have the Part Number I can find the correct curve.

[gduplock]

Thanks for reply Chris,

Distributor no. I think is 0231 159 001 also marked JFDR6.

Not keen to pull it off again.

[chris_seven]

Not keen to pull it off again.

As the actress said to the bishop

I will post the curve for this distributor in the morning.

[chris_seven]

[304065]

As the distributor gets older the springs fatigue and the pivot pins for the flyweights wear. The net effect is to cause the distributor advance range to be much wider than stock.

We make the problem worse, as well as starting more difficult, by using 10 degrees of advance at idle. Chris' reprise of the FWM advance chart for the 001 above shows that the advance measured AT THE CRANK goes from TDC at 900 RPM to 31 degrees at 7000 RPM (which is where the centrifugal rev limiting rotor starts to cut off). That is an advance range of 31 degrees.

If you start at 10 degrees advanced instead of 0 degrees, your final advance will be 41 degrees, which will do this:



How do I know all this? My distributor was doing the exact same thing. Solution is to have the distributor rebuilt.

My Saga is here: http://forums.pelicanparts.com/porsc...ml#post2247381

My original measurements were like this:

[chris_seven]

We bought one of these about 6 years ago and it has been quite useful

[gduplock]

Thanks for the advance chart and advice/warning. Still to measure advance versus rpm with strobe. Hopefully can back off advance a bit from the 8.5 deg static and still achieve smooth running up to top rpm.
Will let let know verdict.
G