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Your power valve is just a srpring and a diaphram that acts on engine vacuum to rivhen up the fuel circuit. It has two number stamped on it. If it has a 6 stamped at 12:00 and a 5 stamped at 3:00, you have a 6.5 power valve. Which is what the vacuum reading will be when it opens. Your number should be about 2-3 less than your idle vacuum. If your motor only pulls 6" of vacuum, than get a 3.5 power valve. It is blown if the diaphram has a hole in it. I would say stick with the 71's for now, check and change your power valve (I ran a 3.5 with a 292 cam in a motor I had) I also had to drill holes in the primary throttle blades next to the idle transfer slot to keep the airflow fast enough to keep the idle circuit functioning correctly. Normal starting point for idle circuit mixture screws is 1.5 turns out from all the way in.
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In a fit of 16 year old genius, I looked down through the carb while cranking it to see if fuel was flowing, and it was. Flowing straight up in a vapor cloud, around my head, on fire.
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