[chopper]

My experience was a little different from those listed above. My car had a set of race-prepped carbs on it when I bought it. The carbs were mechanical secondary and had been worked for drag racing, and as such were unsuitable for the street. Rather than spend a lot of time trying to recalibrate them for the street, I replaced them with a pair of 1860 vacuum secondary units. I spent a good bit of time fiddling with them to get them to run acceptably on the 484 inch stroker motor. I ended up with one size larger than stock primary jets, installed 8.5 power valves and the heaviest secondary diaphragm springs to slow down the secondary opening. I found that with the lighter springs, the secondaries were opening too quickly and causing a major bog. The car runs much smoother now but I do note that it has lost a little bit of punch at the top end in fourth gear. For example, with the mechanical secondary units, I could break the rear tires loose at 3500 rpm just by flooring the pedal; with the vacuum units, it won't do that in fourth gear any more. It does bring in the power more smoothly, however, in the lower gears. Just my experience.

BTW, I've tried to find a pair of the vacuum tops with the nipples and have been unable to do so to date. Does anyone know where I can find a set of these lids? Thanks.