Ignition timing at idle on a '71 T or only 35* at 6000 RPM??

[hessel1974]

Hi,

I am going to check my timing tomorrow and just want to confirm something. My '71 911T is stock and has a Bosch distributor.

I know that the correct timing should be 35 degrees BTDC, but is there also an idle setting? I know that after '71 the timing should be 5 degrees ATDC at 900RPM. Does this also apply for my 911 or should I just focus on that 6000 RPM 35 degrees timing?

Just want to do this right the first time. Don't like sitting in front of a 6000 RPM spinning 911 engine and fan for too long

Thanks for your help!

[Grady Clay]

The timing at 6000 rpm is the critical setting; too much advance and you can damage the engine, too little advance and the engine can run poorly.

Due to variability among distributors, the total range of advance from idle to 6000 rpm can vary somewhat. This is why the timing is set at 6000 rpm and the advance at idle falls where it may.

Best is to set the timing at 6000 rpm and then measure the timing at your idle. There is a range specified. It is also useful to measure the ‘static’ timing; where the spark occurs when turning the engine with a wrench. These let you reinstall your distributor and be close on the timing at 6000 rpm.

It is also important to measure the advance at every 500 rpm or so. You can compare these measurements to the Factory advance curves. This lets you confirm that the various springs and weights are functioning as intended.

Always check that the advance smoothly changes as you [u[decrease[/u] rpm. It is common for the advance mechanism to stick at a higher advance.

Don’t worry about 6000 rpm, it is just noisy.
You can drive all day at that speed.

Best,
Grady

[James Brown]

So, just for my knowledge, on a '71, timing is set @ 6k and idle timing is checked within limits from the graph? (only mechanical advancement). I don't have one but like to learn.

[hessel1974]

Thanks Grady! I have set the timing yesterday and although it goes against every fiber in your body, I revved the car to 6000 RPM and found that the timing was off by 5 degrees (40 BTDC instead of the 35)

So set it to the correct timing and got in the car and noticed the change directly. A smoother ride, better acceleration and less backfire.

But what I did notice is that the advance from idle to 6000 RPM wasn't very consistent. From 900 RPM to roughly 3000 RPM the pulley went from 5 BTDC to about 25/30 BTDC. and it really needed me to rev it up to 6000 RPM to get top the 35 BTDC. Is this normal? I haven't been able to find the graph to show me the RPM's and the degrees advance to check this.

If this is not ok, could it be the springs in the distributor which need replacement? Are they still available?

Thanks again!!

[James Brown]

Grady will chime in but I think there are 2 sets of springs in the dissy (you can look) that are set at 2 differant tensions.

[hessel1974]

Thanks James. Do you know if and where these are available?? I see the springs in PET, but they do not have a part number.

[James Brown]

I'm sure you can get the springs but you should get someone who rebuilds the dissy to set them up properly, not a diy kit.