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On 10 Dec 2002 at 22:10, Steven Ayres wrote: > I'm running an FI distributor with working vacuum advance connected to the > stock vac port on a pair of '66 Solexes tuned for my 1641, with larger jets and > later venturis. With these carbs the vac advance kicks in when the throttles > open and tapers off as they close for cruising. I'm gonna stick to my claim that this is hard on your engine, although I agree that it certainly will "feel" good. Running this way will give you in the neighborhood (depends on which FI dist you have) of 40 deg of advance at full throttle, but you haven't mentioned where it is timed at idle, so I don't really know where you end up. Since I doubt that you're set for any amount of retard at idle, I'd be concerned about the end result you get. The FI vac advance can may not give you its full advance with the Solex vacuum, so this may alleviate things. Your larger venturis will also reduce the vacuum response. I have a friend who races (different cars) and he once set his timing by ear following a late night rebuild session. He was fortunate that one of his friends actually put a timing light on the engine the next morning, before the race, because the max advance was around 70 degrees. While everyone agrees that it might have felt good, it is also likely that he would have burned a piston and not finished the race. Along the same lines I believe Keith was doing the same thing as you at some point and came up with his observation that he could have detonation at high speed and med throttle. In his case also I believe that the cause was actually excessive advance. I eventually checked with my mechanical eng friend who confirmed that extreme advance could cause detonation even under situations that would normally be considered non-typical for knock, but it takes a LOT of advance to do this. Keith is lucky he suffered little or no damage. What few people appreciate is that the max advance figures that are given out for air cooled VWs (30-34 degrees BTDC) are for full power output only, but that the engine can easily tolerate much more advance under light loads. Since this gives better fuel economy, it is often done in the later cars by using the vac advance as I described before. Of course this requires a mechanical advance to take over the work that the earlier dists did with just the (different) vacuum advance. -- Jim Adney jadney@vwtype3.org Madison, WI 53711-3054 USA ------------------------------------------------ To unsubscribe, E-mail to: <type3-off@vwtype3.org> For more help, see http://vwtype3.org/list/