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On 30 Aug 2003 at 21:16, Mark Seaton wrote: > A while back I reported that I could see no difference to the advance > behaviour of my distributor with the vacuum hose connected or disconnected. > Well today, after a few days of rougher running than usual, I checked it > again with my timing light and discovered something that I think is wrong. > With the hose attached there is a defnite difference: if I rev the engine to > just 1200 rpm the advance flips to full 30+ degrees of advance! and it > slowly climbs past that if I continue to rev. With the hose detached the > advance is much more subtle and as would be expected. This is very odd. On dists with mech AND vac advance, the vac advance is almost NEVER responsible for more than 10 crankshaft deg of advance. > I've heard Jim say that you should not see any difference with the hose > attached and the car stationary so I'm guessing that this is wrong, and bad! > > Its almost as though the vac can has failed by its spring breaking or > something? Not a vac leak as I would think more usual. So the question is > what can I do? Can I fit a bug vac can? Or what are my chances of finding > the correct can? Is there any chance that the carbs you have are not the ones that came with this distributor? Does this dist have a vacuum retard as well as a vacuum advance? Put a clean piece of hose on the vac can and suck on it while you watch the timing. What happens? You'll know from this test whether you have a vacuum advance, or perhaps a vacuum retard, and whether the spring is broken (I've never heard of this happening.) You can actually do this test with the engine running AND with the engine stopped and the dist cap off so you can watch what's happening. Each method is useful in different ways. If the vac can needs to be replaced it is probably still available. Bosch dealers have listings and there is a 3 digit number stamped on the connecting arm which is the last digits of the Bosch 10 digit part number. What number is there? Were you the one who figured out that different stock carbs came with different vacuum ports in different eras? -- ******************************* Jim Adney, jadney@vwtype3.org Madison, Wisconsin, USA ******************************* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org