HIS, all of the later carburetors have the holes on the air horn to add POE. Dig through a pile of later airhorns and many will have POE (6 brass tubes instead of 4). Much better in design than the early POE, as those carburetors robbed fuel from the supply passages to the secondary fuel nozzles, later POE pulls fuel from the main fuel bowl. I DO NOT like or use the early POE carbs for serious high performance applications. The POE works against you. It becomes more difficult to dial in the correct secondary metering rods as we have no control over the airbleed size and the huge brass tubes take up a LOT of room in the fuel supply passages.
The power piston spring used really has little if any effect on fuel economy. Use the strongest spring that will stay down at idle, this provides best throttle response and power on a well set-up carb. If you move up to a post 75 carburetor with APT for the power piston, you can dial the A/F in exactly for your combination. This is much easier and more precise than changing jets/rods in the early units. You also get the later float arrangement, which is superior in every respect than early units.....Cliff
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