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06-19-2014, 01:43 PM | #1 |
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How does the power valve work
Simple Question I know but I have few reference materials
for the later flatheads. Does the gas flow down the stem into the body when vacuum is low? Is there any other test besides the overnight drip test? Thanks
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06-19-2014, 01:45 PM | #2 |
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Re: How does the power valve work
If your engine is running, you can try to screw the idle mixture screws all the way in. If the engine shows no difference in idling, chances are the PV is kaput.
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06-19-2014, 01:48 PM | #3 |
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Re: How does the power valve work
In some instance's, the power valves work best, when left on the work bench... Ask me how I know...
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06-19-2014, 02:13 PM | #4 |
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Re: How does the power valve work
Here's how I think they work. The engine starts and the vacuum pulls on the diaphragm and shuts the valve. As the vacuum drops (when pulling hard, or accelerating), pull on the diaphragm diminishes and the valve seat opens this allows the carb to draw extra fuel through the passages in the valve body. No fuel passes through to the chamber below, this is (supposed to be) a vacuum chamber for the engine vacuum to act on the diaphragm of the power valve.
Note the vacuum pulls the valve shut and opens it as it falls. If you have a hot cam you will have less vacuum at idle. To stop the valve opening prematurely you fit a lower number power valve. That means it takes less pull from the vacuum to keep it shut. Only when the vacuum falls below a lower value than with a stock valve, will it open. I changed the valves on my roadster last night (twin 94's) and the chamber on the front one was bone dry. The vac chamber on the rear one was wringing wet with fuel. From that I presume either the diaphragm was shot or the valve wasn't seating properly. Anyway, it did drive better afterwards so I think the fuel leaking past the rear power valve was causing a problem. Changing the cam from a Isky Max1 to a Schneider 270F reduced the vacuum at idle hence the need to swap out the valves. Mart. |
06-19-2014, 05:09 PM | #5 |
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Re: How does the power valve work
Test it by sucking on it. If it holds to your tongue it is good.
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06-19-2014, 05:32 PM | #6 | |
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Re: How does the power valve work
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Quote:
Thanks, Gene |
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06-19-2014, 05:42 PM | #7 |
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Re: How does the power valve work
Here's a good picture from a Ford manual. You can see the seat on the stem of the PV.
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06-19-2014, 05:57 PM | #8 |
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Re: How does the power valve work
Good explanation Mart.
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06-19-2014, 07:26 PM | #9 |
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Re: How does the power valve work
If you want to test a power valve, this works....
http://www.summitracing.com/parts/mor-62295 Lonnie |
06-19-2014, 07:28 PM | #10 | |
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Re: How does the power valve work
Quote:
Brian
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06-20-2014, 08:58 AM | #11 |
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Re: How does the power valve work
Good job Mart !!!!!!
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