SWB distributor advance

[Fritter]

Printout showed everything was between the high and low specs. The springs could be both weaker and too short, which could cause some advance to come in at 900 RPM and also only 20 degrees or so total advance. And also a slow return to the correct idle after hitting the gas. I talked to Ed last night and I'm sending it to him for analysis, so we'll see what happens.

[Flieger]

There seems to be two opinions on weak springs' affect on advance. I have not seen the distributor being discussed, but if normal total advance is reached with the arms up against a solid stop or with the arms all the way out, then weak springs would cause the advance to come in earlier and come down lower. If the springs were not only weak, but stretched, then the advance range would be less because the arms would not return all the way. If the springs still set the maximum advance, then I suspect the range would still be a little less because the spring would work harden as it stretched, making the spring stiffer but longer.

[BURN-BROS]

When the springs get weak you end up with MORE total advance not less. That's why old cast iron distributors give you a high idle and backfires-- it's because the distributor advance range is like 45 degrees, so you set the top end to be 35 at 6000 rpm and you end up with 10 degrees of advance at idle, too much. You have the opposite problem.

This is true, BUT when you re-adjust base timing @ idle the result is not enough timing. It's a very common result because people seem to have a problem with setting timing @6000 rpm. This scenerio is most likely Mike's problem.

Edit; actually the total advance will not increase due to the design. it will however, reach full advance sooner.

[Bruce M]

or......

another possiblity is you're strobe gun is not very accurate. This is pretty common even with some of the $$$ tool brands (especially the guns with the adjustable advance dial).

Getting a re-test on the proper dissy tester will confirm.

[Fritter]

Good point on the strobe light. I did check at 6k RPM so I believe advance might be coming in at idle. Ed Fall has it now so the final judgement remains to be seen....to be continued.

[NeunElf]

According to the shop manual [11 LI] an early 911 should show 30° BTC at 6000 rpm without load or 32° BTC at 6000 rpm with load when set at TDC (engine not running). For an early 911S it’s 30° BTC at 6000 rpm with or without load when set at 5° BTC (engine not running).

I think Figure 75 applies to a '68.