The aforementioned dual quad testing was performed on a +060 over 312 that uses an older Crower 238° @ 050”camshaft. Depending upon the heads being used, the static cr is 9.1-9.6:1. This particular short block would have been a pretty typical build for many of the performance Y builds in the 50’s & 60’s. The Lincoln T-Pots on this engine did outperform both the factory dual quad carbs (which included both List 1268’s and 1434’s) and a pair of modified List 1161’s in most instances so over-carburetion with the Lincoln Teapots on this particular combination is not an issue. Port work on the intakes is always a big help as the HP numbers with ported intakes really takes off with the larger carbs.
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The fuel bowl covers on both sets of Lincoln carbs used in the dual quad testing are #48's. As delivered from the factory, those covers contain air bleed holes that are sized as per application. On the Teapot dual quad applications, it’s important that the same ‘numbered’ covers be used on each carb. By using the wide band oxygen sensors on the dyno, the fuel curve throughout the rpm range can be evaluated and modified as deemed appropriate. The key here is having a fuel curve that’s consistent throughout the rpm range and not lean on one end and rich on the other. Swapping covers can alter the idle and/or high speed fuel mixtures depending upon the bleed hole sizes. Cover changes by number are a quick way to do this once the various hole sizes are measured. To do this you’d need a stack of the various covers in lieu of either soldering up holes and redrilling or making the existing holes larger.
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If the brass tubes to which you refer are the tubes that protrude from the bottom of some of the Teapot covers, those are necessary to richen up the high speed circuit. Removing them may cause a serious off idle stumble while also creating a lean condition jetting changes cannot fix. I’ve found that the idle bleed holes in the Lincoln Teapots are on the large side when using them as pairs on the smaller cubic inch Y’s. Sticking various sizes of small diameter wire in those holes on both carbs while running the engine at idle helps to determine exactly what hole size is ultimately needed for the idle mixture. With the right size idle bleed hole in place, the idle mixture screws are happy at ~1 turn off of closed.
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As a general rule, whatever jets are correct for a single four barrel application will be too large for the same carbs when used as pairs. This is simply due to the reduction in cfm that takes place through each carb when using them as pairs. The larger the carbs, the more sensitive they are to jet changes. For the optimum air/fuel ratio when switching single four barrel carbs to dual quad pairs, the jet sizes in both the primaries and secondaries are reduced accordingly. Otherwise the carbs tend to run on the rich side.
Lorena, Texas (South of Waco)