Author Topic: blown power valve on 440-6  (Read 346 times)

Offline 351c4v71

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blown power valve on 440-6
« on: July 31, 2017 - 08:08:26 pm »
Hi guys,
Gotta blown power valve on my 71 cuda 440-6.
How do I measure the vacuum to determine what size my replacement power valve should be. I have the gauge but not sure where to plug it  :clueless: exactely . I guess engine should be at running temp.
Then, to remove the center carb... do I need to remove the back carb. I think I read somewhere it's possible to slide the center carb towards passenger side without removing the other carbs.
Finally will any 2 barrel holley rebuild kit work to rebuild the center carb. I have the #37-1543 kit already.
Thanks
JS




Offline cudabob496

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Re: blown power valve on 440-6
« Reply #1 on: July 31, 2017 - 09:30:55 pm »
how did you determine valve is blown?

on 4150's, if shut all 4 corner idle adjust screws, and engine does not stall,
indicates power valve is bad.
« Last Edit: July 31, 2017 - 09:32:26 pm by cudabob496 »
72 Cuda, owned 25 years. 496, with ported Stage VI heads, .625 in solid roller, 254/258 at .050, 3500 stall, 3.91 rear. 850 Holley DP, Reverse manual valve body.
Up to 4000 RPM, Warp Speed, Up to 5000, Rediculous Speed, Up to 6000 RPM, Ludicrous Speed!

1999 Trans Am, LS1, heads, cam, headers, stall, etc! Love to surprise the rice rockets with this one. They seem so confident, then it's "what the heck just happened?"

Offline jhaag

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Re: blown power valve on 440-6
« Reply #2 on: July 31, 2017 - 11:04:13 pm »
You want to measure full manifold vacuum at idle, warm, in gear if an automatic. This would be from a source below the throttle blades. Power valve should typically open a 1/2 idle vacuum, ie if you have 12 inches of vacuum at idle, a power valve rated for 6 inches of vacuum is what you want. Not sure about your carb kit, but if you carefully compare the gaskets, it may work. Can't answer question about carb removal.
love 70 Challengers


Offline 351c4v71

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Re: blown power valve on 440-6
« Reply #3 on: August 01, 2017 - 07:07:37 am »
Car runs super rich , I closed both idle screws and engine kept going. So power valve is blown.

Can I measure vacuum on the middle carb?  I just can't find exactely where to conect the gauge on a 6 pack set-up. Car is manual btw.

Thanks

Online KillerBee

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Re: blown power valve on 440-6
« Reply #4 on: August 01, 2017 - 08:18:24 am »
Back of the intake manifold below the rear carb there is a plug.

Remove/replace the plug with a plug with a barbed end to connect to your vacuum gauge, then put a rubber vacuum cap on it when done.
More than likely you will be using the port again to check vacuum when tuning the carbs.

I would be surprised if the power valve is blown. :2cents:

I've never had good luck trying to just remove the center carb.
« Last Edit: August 01, 2017 - 10:40:15 am by KillerBee »

Offline AARuFAST

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Re: blown power valve on 440-6
« Reply #5 on: August 01, 2017 - 08:48:04 pm »
I have had my 340 6 pk apart many times,   If I recall the back is removed first then the front- center reverse order install.
1970 AAR Cuda
1970 Gran Coupe Ragtop. 1 of 66
Gran Cpe Convertible 1 yr only.

" I Want to Ride "

" I tried to be normal once...
it was the most boring
2 minutes of my life!!!!"

Offline 69bcuda

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Re: blown power valve on 440-6
« Reply #6 on: August 02, 2017 - 02:45:53 pm »
There's this...........

Power Valve Check Ball Kit
PART# 125-500

https://www.holley.com/products/fuel_systems/carburetor_components/power_valves/parts/125-500

Offline 351c4v71

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Re: blown power valve on 440-6
« Reply #7 on: August 02, 2017 - 07:05:50 pm »
Thanks
I also read about a power valve plug
Anyone tried this? Whats the disadvantage to have it plugged?

Offline AARuFAST

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Re: blown power valve on 440-6
« Reply #8 on: August 02, 2017 - 09:20:33 pm »
Thanks
I also read about a power valve plug
Anyone tried this? Whats the disadvantage to have it plugged?
Block power valve is for racing.  Not good for local driving..
1970 AAR Cuda
1970 Gran Coupe Ragtop. 1 of 66
Gran Cpe Convertible 1 yr only.

" I Want to Ride "

" I tried to be normal once...
it was the most boring
2 minutes of my life!!!!"

Offline AARuFAST

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Re: blown power valve on 440-6
« Reply #9 on: August 02, 2017 - 09:23:01 pm »
Some infor on 6 pack tuning.
1970 AAR Cuda
1970 Gran Coupe Ragtop. 1 of 66
Gran Cpe Convertible 1 yr only.

" I Want to Ride "

" I tried to be normal once...
it was the most boring
2 minutes of my life!!!!"

Offline 351c4v71

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Re: blown power valve on 440-6
« Reply #10 on: August 03, 2017 - 10:18:17 am »
Just ordered the check ball to protect against power valve blow out

Offline 351c4v71

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Re: blown power valve on 440-6
« Reply #11 on: August 03, 2017 - 10:31:33 am »
what is the proper carb rebuild kit part # for the center carb.?

Offline ed-pv

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Re: blown power valve on 440-6
« Reply #12 on: August 13, 2017 - 09:04:55 pm »
I changed out the jets in my center carb and I was able to remove the center carb alone.

Offline Aracer

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Re: blown power valve on 440-6
« Reply #13 on: September 08, 2017 - 05:57:47 am »
      The 5 hg PV is the only one to use. Springs are strange on the lesser #'s.    Higher # will be leaking gas constantly, in traffic when the throttle is flipped to quick.
     Stupid design, gas on one side, vacuum on the other looking for a flaw.  Stock up ahead.