on my 4160c the power valve is a 65 which i believe is wayy too big causing a rich condition that clears around 3000 and it takes off somewhat.

on my 289 we're thinking of going with a 35 or a 45 power valve to bring it down and actually give the car its power it needs, anyone know anything about power valves or what the stock was on the old 4 barrel, granted mines a new holley 600cfm.

 

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Holley now says that the PV size should ideally be about 2" lower than idle vacuum in a performance app. I'm only running about 12.5-13" of idle vacuum, and it runs great with a 10.5 PV. Pings at part throttle with a smaller valve. A stock engine is going to be higher restriction, so even a "big" power valve won't open until you really have your foot in the throttle. It sounds like it could be ignition timing, or the accelerator pump curcuit, or it could be jetting, or the low speed air bleeds could be clogged. What exactly is it doing?

 

its "slow" til it hits around 3k and takes off like crazy and it loads up at idle somewhat. i'm also attributing the secondaries are not opening or are barely opening due to the fact on another forum and based from Holley the stock "Black" spring is too heavy for my car and engine and i should drop oit to the mid Yellow spring so they actually open all the way. we're replacing the power valve with a 4.5 as i'm pulling around 12-14 hg.

i'm also attributing to it possibly being out of time slightly. everywhere i've looked a 289/302 with GT40P heads runs better with less total timing than what i have. i'm at around 12 then at full advance around 38 when i should be at around 32-34. my plugs could be gapped too close also @ the stock 289 of .035 so i'm thinking of backing it up to around .040

 

If you're power valve isn't damaged, it's not the power valve. 4.5 is a SMALL power valve that is really only used on race cars with large cams. On a street car with 12-14" vacuum you're basically gonna run too lean under part throttle load with a 4.5 PV. Either the valve is damaged, the carb is set wrong, or you have an ignition problem. What's the advance curve like? What rpm is total advance in by? Also, if it's an older carb without PV blowout protection, and you had any intake backfires, you could have ruptured the diaphragm in the valve. Does it flood at idle and load up real hard the longer it sits?

 

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