Holley problem: leaking power valve? - Page 2 - Chevelle Tech
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post #16 of 37 (permalink) Old Nov 13th, 19, 5:28 PM
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Re: Holley problem: leaking power valve?

Brass, always brass. Nitrophyl tend to lose their coating, saturate, and sink, foam degrades faster than the Nitrophyl, especially with "gasahol" fuel mixes.

As far as the PV leaking, if that was happening, the carb would lose fuel into the manifold, and eventually into the pan when the engine was shut down, to the bottom level of the PV leak. If it were severe, one cylinder could fill with fuel, and when attempted to restart, bend a rod, kill a piston, etc.
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post #17 of 37 (permalink) Old Nov 13th, 19, 5:47 PM Thread Starter
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Re: Holley problem: leaking power valve?

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Originally Posted by Dave Ray View Post
Brass, always brass. Nitrophyl tend to lose their coating, saturate, and sink, foam degrades faster than the Nitrophyl, especially with "gasahol" fuel mixes.

As far as the PV leaking, if that was happening, the carb would lose fuel into the manifold, and eventually into the pan when the engine was shut down, to the bottom level of the PV leak. If it were severe, one cylinder could fill with fuel, and when attempted to restart, bend a rod, kill a piston, etc.
The bowl was still full of fuel, up to the sight plug at least so it never got to that point.

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post #18 of 37 (permalink) Old Nov 13th, 19, 8:22 PM Thread Starter
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Re: Holley problem: leaking power valve?

Is there anything in the main body or the throttle plate that would be compromised if I submerse these parts in parts cleaner? The parts washer I have is filled with pretty mild cleaner but it does a good job of dissolving grease. It is not the super aggressive carb parts dip that gives you cancer if you look at it sideways.

The rear bowl had just a tiny bit of dirt in it. The power valve holds a vacuum and the needle valves both looked good but are still going into the dustbin.

I visited Eric's website and was interested in the page about how gasket mating surfaces are rarely as flat as they should be. I found this to be entirely true in my case. I gently sanded the metering block faces of the main body and the base of the main body to take down some of the high spots. The main body has a fairly rough surface in these areas and I'm not going to keep sanding to completely eliminate them (it would take days and days) but I got them much better. Nothing left that the gaskets can't easily take care of.

Concerning the choke plate screws, when I put them back in would blue loctite be sufficient to keep them in place? Same question on the throttle plate screws. I know the throttle plate screws all have lock washers on them but a little extra security never hurts as long as it doesn't damage the screws or main body screw holes.

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post #19 of 37 (permalink) Old Nov 13th, 19, 8:49 PM
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Re: Holley problem: leaking power valve?

I'd install the PV protector. Like anyone would ever know short of rebuilding the carb. Before it was a part you could buy we would drill the hole oversize cut the spring from a ballpoint pen to length put a small steel ball on top of the spring then reassemble the carb. If you don't install it you better hope it never backfires.
It's only original once, so I guess you better not use the blue gaskets either. BS

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post #20 of 37 (permalink) Old Nov 13th, 19, 10:36 PM
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Re: Holley problem: leaking power valve?

I use blue locktite on the screws and a file on the main bodies when needed. I never dip base plates because you can push dirt into the shaft bushing and you'll never get all the solvent out without removing the shafts but the only thing to worry about is the Teflon srips on the throttle shafts.

We've all heard about backfires rupturing power valves and Holley took steps to keep it from happening but I've never actually seen it happen. Keep your tune right, don't lean on it when it's cold and you shouldn't have to worry about a $5 power valve. I've never understood all the pearl-clutching about power valves- they're cheap and easy to replace. I must have 20 6.5s laying around that I'll never use.

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post #21 of 37 (permalink) Old Nov 14th, 19, 7:32 AM
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Re: Holley problem: leaking power valve?

ditto on the pv protector no reason not to

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post #22 of 37 (permalink) Old Nov 14th, 19, 9:30 AM
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Re: Holley problem: leaking power valve?

Take this for whatever it's worth;

I've been rebuilding carbs for 40+ years, professionally for 20. I have literally built thousands of Holley carbs, and I haven't installed a power valve blowout protector in a single unit.

The number of come-backs I've had due to a blown power valve?

Zero.

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post #23 of 37 (permalink) Old Nov 14th, 19, 12:42 PM
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Re: Holley problem: leaking power valve?

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Originally Posted by Vintage Musclecar View Post
Take this for whatever it's worth;

I've been rebuilding carbs for 40+ years, professionally for 20. I have literally built thousands of Holley carbs, and I haven't installed a power valve blowout protector in a single unit.

The number of come-backs I've had due to a blown power valve?

Zero.
I have a buddy who is one of those guys for whom every silver cloud has a dark lining. He was always lamenting "there goes the power valve" after the slightest spit / stumble of the engine. Seemed like he wanted a reason to take the carbs apart? I seriously doubt he actually had many failures (if any) and I am SURE he did not have any where the number of failures he fretted about.
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post #24 of 37 (permalink) Old Nov 14th, 19, 1:22 PM
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Re: Holley problem: leaking power valve?

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Seemed like he wanted a reason to take the carbs apart
I invent reasons to take perfectly fine cabs apart all the time because I like to. But the only bad power valves I ever find are just plain old. They dry rot and crack from sitting. I've goofed a tune or two in my time and had some pretty epic backfires and none of them damaged a power valve. The 307 in my Malibu has at least one, probably several, bad intake valves and sneezes HARD and repeatedly through the carb at anything over half throttle. It has an 1850 on it that doesn't have power valve protection and hasn't damaged one yet.

And for Pete's sake- a power valve costs practically nothing and takes a couple minutes to change!

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post #25 of 37 (permalink) Old Nov 14th, 19, 7:29 PM
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Re: Holley problem: leaking power valve?

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Originally Posted by Tommy the Cat View Post
I invent reasons to take perfectly fine cabs apart all the time because I like to. But the only bad power valves I ever find are just plain old. They dry rot and crack from sitting. I've goofed a tune or two in my time and had some pretty epic backfires and none of them damaged a power valve. The 307 in my Malibu has at least one, probably several, bad intake valves and sneezes HARD and repeatedly through the carb at anything over half throttle. It has an 1850 on it that doesn't have power valve protection and hasn't damaged one yet.

And for Pete's sake- a power valve costs practically nothing and takes a couple minutes to change!
Maybe you mised my point. I was agreeing with the premise that there is IMHO too much focus on the perceived ease of damaging those power valves. IMHO even EPIC backfires don't necessarily kill the PV. I didn't care if he changed the valve everyday same as people change their underware or brush their teeth every day. I was just fed up with hearing the lamentations caused by even sub epic level backfires.
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post #26 of 37 (permalink) Old Nov 14th, 19, 8:17 PM
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Re: Holley problem: leaking power valve?

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Originally Posted by oman View Post
Maybe you mised my point. I was agreeing with the premise that there is IMHO too much focus on the perceived ease of damaging those power valves. IMHO even EPIC backfires don't necessarily kill the PV. I didn't care if he changed the valve everyday same as people change their underware or brush their teeth every day. I was just fed up with hearing the lamentations caused by even sub epic level backfires.
No I got what you were saying. I was just saying I take perfectly good carbs apart just for fun, joking that I can relate to your friend, though for very different reasons.

I probably should've started another paragraph for the rest of what I posted after my bad joke so it didn't seem it was directed at you. Seems like our opinion is the same as far as power valves are concerned. Sorry for the confusion.

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69 Malibu Stock 307, Reverse Manual TH350, 4,500 Stall Edge Converter, 4.56 Spool 35 Spline 12 Bolt

76 C20 VortecPro 496 628HP 655 lb/ft TH400 Edge Converter, 4.10 14 bolt
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post #27 of 37 (permalink) Old Nov 14th, 19, 8:36 PM
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Re: Holley problem: leaking power valve?

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Originally Posted by Tommy the Cat View Post
No I got what you were saying. I was just saying I take perfectly good carbs apart just for fun, joking that I can relate to your friend, though for very different reasons.

I probably should've started another paragraph for the rest of what I posted after my bad joke so it didn't seem it was directed at you. Seems like our opinion is the same as far as power valves are concerned. Sorry for the confusion.
No sweat Tommy. "No harm no foul" as the saying goes.

It is very refreshing to see your last post. Most people today have no knowledge of the purpose of a new paragraph in a composition. Some of the material I read these day shows absolutely no indication of knowledge of composition rules / possession of composition skills. Everyone makes mistakes, everyone has oversights but some folks don't even have a clue about the rules that they are not applying. No sweat here on my end as far as your earlier response to me!

Yes we do agree on the subject of PV failures. I have had my share of epic backfires and I cannot recall ever killing a power valve. That is the reason I took just shook my head and rolled my eyes whenever my firend, "Mr. Doom and Gloom", went off on another tear about killing another PV because of whatever event he concluded had killed his current PV.
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post #28 of 37 (permalink) Old Nov 14th, 19, 10:26 PM Thread Starter
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Re: Holley problem: leaking power valve?

All the parts are cleaned up so the rebuild can begin this weekend. In fact, I think the old 37-119 Trick Kit I have may have enough parts to do the rebuild. I could take the new one back or just put it on the shelf for future use. I must have bought the kit years ago, probably to get one or two little parts I needed at the time.

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post #29 of 37 (permalink) Old Nov 14th, 19, 10:33 PM
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Re: Holley problem: leaking power valve?

If you need any small parts to keep from having to open the new kit please let me know. I buy all the parts individually and in bulk so I have a small speedshop's level of supplies. I'd be happy to send you whatever you're lacking.
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69 Malibu Stock 307, Reverse Manual TH350, 4,500 Stall Edge Converter, 4.56 Spool 35 Spline 12 Bolt

76 C20 VortecPro 496 628HP 655 lb/ft TH400 Edge Converter, 4.10 14 bolt
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post #30 of 37 (permalink) Old Nov 14th, 19, 11:09 PM
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Re: Holley problem: leaking power valve?

I only dress the threaded metering block boss ends of the body for flat, as the screw hole bosses bend easily when some Gorilla uses 57 foot pounds of screw torque to hold a leaky metering block in place after it was bent so far out of shape it won't work.

For the metering blocks, I lay them out with their bent curvature up in the center, and VERY LIGHTLY press them back flat. Way too easy to turn a metering block into instant junk with other methods.

Before I get plastered by everybody for what I am saying, please remember, I worked in the Pro-Stock carb dept of Holley Racing for 5 years, band sawing Dominator's apart, making them into "Split Duals", then helping tune them on race cars.

As far as the leaking PV, a few ways to get them to leak, frm the wrong gasket, to the over tightening in the metering block, but what aI was asking, and got the right answer, was, did the vacuum diaphragm get punctured, was there fuel leaking into the manifold? I have seen a very small tear in a PV diaphragm load the entire bowl volume down to the hole, into the intake manifold, cylinder, and oil pan. NONE of ahy of that is good at all. Glad that wasn't the issue.

The PV save device is simply to make sure the PV diaphragm doesn't have failure issues if the engine backfires. The reverse pressure can easily kill the PV diaphagm.
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