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On 17 Sep 2002, at 4:18, Dave Hall wrote: > I read this as meaning the manifold vacuum advances the timing 7deg at idle > but the carb vac retards it that much, leaving timing at TDC while idling > (that's why it's set at 0deg hoses on for the twin carb twin vac!). > What worries me here is that Ben is timing at TDC as is normal for that > model, but with the wrong distributor. I'm only familiar with the 72 adv/retard dists on the US beetles and type 3s, but I'd be willing to bet that they are similar. The advance and retard don't really act at the same time at all. The retard only works at idle and the advance only comes into play while cruising. What Ben should do clearly depends on how much advance he gets from his dist, but most of the FI dists give about 30 deg of mech adv so timing at TDC is about right. Any vacuum advance is in addition to this, but it only comes into play at high rpm/partial throttle, when you can tolerate more advance. This simply give better fuel economy when cruising. > I've just checked the '69 AT injection Fastback vehicle analysis (by the UK > Motor Industry Research Association) and their figures show the vac advance > for 311 905 205L as 0 at 2000 crankshaft rpm (4" Hg manifold vac), > increasing linearly to about 10 deg at 3,800 (7.8" Hg manifold vac). > Centrifugal advance goes from 0deg at 1000 rpm to 20 at 2000, then maxing at > 30 deg at 2800 rpm. Fascinating figures, but does it help here? ;-) > Clearly it's not with WOT, but partial throttle and above idle engine speed, > as you said, Jim. This data is also shown nicely in the Bentley manual as well as those for all the rest of the 68-73 US dists. - ******************************* Jim Adney, jadney@vwtype3.org Madison, Wisconsin, USA ******************************* ------------------------------------------------ To unsubscribe, E-mail to: <type3-off@vwtype3.org> For more help, see http://vwtype3.org/list/