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----- Original Message ----- From: "Jim Adney" <jadney@vwtype3.org> > Are you sure this is how they are? I'd expect the port drilling to come in just > ABOVE the butterfly. Do you see a large vacuum at idle? Your description > actually sounds like the way the port would be drilled for the vacuum retard > found on distributors with vacuum advance AND retard. I will have to check now as I have to admit I was writing from memory. > Forgive the stupid question, but is there any chance that the throttle bodies > have gotten misassembled and are not upside down? That would put the port on > the wrong side. They would not work at all if I had as the passage of fuel for the idle jet has to pass from the main carb to the throttle plate via a gasket with cutouts in it. You've got me wondering now if I installed the butterfly plate the wrong way round but I don't think that could be made to work at all either because of the linkage. > Is there any chance that there is another port up in the carb, in the venturi? > Or there could be a second port somewhere on the throttle body. Not on these carbs but I have seen this on others > Another test that I'd suggest would be to put a Tee in the vacuum line and then > run an extra line up to a gauge next to you while driving. This way you could > note how much vacuum you actually get in various driving situations. You should > be able to make a chart of vac vs. vac. advance and then tell us how much vac > advance you're actually getting under various situations. I'd like to try that but I'm not sure how I'd log it all- particularly the mechanical advance which I'd need to work out the vac advance. I'll have to have a longer think about this! > You should also be able to take your Bosch distributor part number to a Bosch > dealer somewhere and get them to check to see if the 507 vac can is the right > one for it. My Bosch parts catalog just lists the US parts, so the 507 doesn't > appear in it (but the US FI 73s got a 505, so we're close enough that this > seems likely to be correct.) > Yes that sounds too close to be very wrong > > Before I re-fitted the original carbs I had some other older carbs on there > > and those did an even stranger thing with the vacuum in that the advance > > would rise rapidly on acceleration but then would take a long time to get > > back down again like there was a vacuum lock somewhere. > > It's quite possible to get dirt in the drilled port which would make it slow to > come to equllibrium. I suppose it's possible that some loose dirt in there > could make a sort of check valve. A possibility I supose. or a misaligned gasket- too late to find out now becasue tey are back in my "bits of carb box" Mark ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org