Author Topic: Power valve block off  (Read 2399 times)

sharpd12

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Power valve block off
« on: June 19, 2016, 09:04:02 AM »
Hey everyone. I just took apart a carb (4412) that I had picked up as a spare. Going through it and found a power valve block off in place of the valve. Anyone have any info on these and what they do and if there is pros or cons

troyer49

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Re: Power valve block off
« Reply #1 on: June 19, 2016, 05:42:59 PM »
Here is a quick read. I know that a carb with the wrong one or none will pulse at part load part throttle not cool on the street  :-)
http://www.chevelles.com/forums/18-engine/281312-why-block-off-power-valve.html
http://www.enginebuildermag.com/2013/01/the-truth-about-power-valves-used-with-holley-carburetors
Good luck
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John_unaman

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Re: Power valve block off
« Reply #2 on: June 21, 2016, 11:03:02 PM »
Sharpd12, there are very few situations where you would use a 4412 without a power valve, if this is for V8 engine circle track use, then this is a very good baseline, check the two holes behind the pv in the block and they should be .058 - .063 in size, if not in that range that block won't work well for you until you fix the two holes, start with a 6.5 pv and if you are a raw rookie who sometimes has overheating problems especially on slippery nights then you step up the pv to an 8.5 or higher, now you need a set of jets either #73 or #74, either set is decent for a beginner, check the air bleeds inside the choke horn the outsides should be .070 - .072 and the inners should be .032, be carefull on the inners they are very sensitive to size, with the engine running check the float levels ( be carefull of fuel running out if the float is too high ) have some one with you to shut off the engine in case the float is too high, ( shut off engine to set the float as fuel will spray out at the screw when you loosen it ) normally I loosen the float screw and if the float is high I would turn the 5/8 nut into the carb while keeping the screw loose about 2 - 3 flats of the nut until you get the float to just weep out of the site hole when you bump the fender slightly. THIS IS ONLY A STARTING POINT , after that you need a pro to look at it BUT this will run with no real issues until you get some laps on it. If your in trouble call my shop and ask for me John Sr. or my son John Jr. 585-424-4131 and tell him about this info as he will not know what you are talking about, he can do the carb with no issues. hope this helps ya. john sr.