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The only thing I'd add to Jim's excellent summary is to look carefully at where the "vacuum" port is coming off your carb, if that's where you're taking vacuum. Many have several taps, and some give downright WACKY results. I have a Weber DGAV that has a port that gives NO vacuum at idle, but as soon as you crack the throttle, it pulls almost full vacuum, and drops progressively as you floor it... I think it was set up to retard timing at idle to reduce emissions and smooth out the idle. Toby B > Sorry, don't have a chart, but here is a summary. > > In a normally aspirated engine, the intake manifold pressure is > always less that atmospheric. the greatest vacuum (lowest > absolute pressure) occurs under engine overrun at high RPM, while > the least vacuum (highest absolute pressure) occurs at low RPM > with WOT. On the road the range you can observe may be nearly a > full atmosphere, but working on your car in the driveway you will > only see maybe 1/2 - 2/3 atmosphere. > > Jim > - > Jim Adney jadney@vwtype3.org > Madison WI USA ------------------------------------------------------------------- List info at http://www.vwtype3.org/list or mailto:help@vwtype3.org