For those who regularly need to adjust calibrations on carburetors, here is a handy chart, courtesy of the Carter Carburetor Company: Drill bit sizes, diameters, areas Was going through some of the Carter tool documentation, and found the chart. Jon.
DO NOT drill Holley jets indiscriminately. Holley jets are not measured by drill size but by fuel flow. Two different jets CAN have the same "drill" diameter. And when drilling jets in general, drill with a "Pin Vise" (hand held tool)...NOT an electric drill motor. Unless you set up a mill and tooling, you'll never get a clean, straight hole with an electric drill motor. Mike
I'm not sure its Holly that measure by fuel flow. Holly now owns Quick Fuel and they have the same tech support. On one call I was told that QF and Holly were different and that Holly used drill sizes and QF uses fuel flow. The next call to a different tech said they were both the same. The facts in my frustrating experience is that Holly jets marked 73 and QF jets marked 73 are visibly different and are approximately 4 drill sizes different. This is comparing new Holly Jets from Summit vs QF jets direct from QF. I now use jet size tools to check sizes.
I use the tail stock chuck in my lathe. Found this to give the truest orifice. For early Stromberg jets (double D), had to make a fixture to hold them (actually 3 fixtures, as there are 3 different sizes). Jon.
Weber I just buy new main jets , not worth the time to drill, anything else I’ll drill. I’m not worried about how they were originally sized. If I have to go up a size I drill, down, solder and drill. I’m aware that my drill size may not flow the same as a new jet but how does that matter if the engine is happy?
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