What are symptoms of a blown power-valve? - Team Camaro Tech
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  #1  
Old Sep 4th, 09, 01:54 PM
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Default What are symptoms of a blown power-valve?

It's a Holley... duh. I've had a few backfires through the carb and I have heard that Holley's can have issues with that.

How would I know if the power-valve is blown without taking it apart?
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Old Sep 4th, 09, 02:26 PM
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Default Re: What are symptoms of a blown power-valve?

A blown Power Valve acts like it is open all the time resulting in a Dramatically over rich mixture at Idle and no response when adjusting the Air Screws.

If your Vacuum at Idle is say 10Hg's you should run something like 6.5 Hg Power Valve so that it only opens when you blip the throttle when the Vacuum drops.

A Vacuum Advance Canister on the Distributor works on the same principle but opposite such that you have full vacuum advance at Idle and Cruise and reverts to mechanical advance when the throttle is punched and the Engine vacuum has dropped.
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  #3  
Old Sep 4th, 09, 03:00 PM
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Default Re: What are symptoms of a blown power-valve?

a "Blown" power valve would be one with a torn or holed diaphram. This would feed lots of raw fuel right into the manifold under the throttle blades. I doubt the car would even run, it would be horribly blubbery rich.

Take it out and suck on it. If air passes thru, it is blown.

Worth noting that when a good power valve is open (manifold vacuum is lower than the number stamped on the valve) it permits fuel to flow into the main wells from the power valve channel restrictor, allowing a metered amount (generally the equivalent of 4 main jet sizes) of extra fuel to come in.
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Old Sep 4th, 09, 03:03 PM
Steptoe Steptoe is offline
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Default Re: What are symptoms of a blown power-valve?

Quote:
I have heard that Holley's can have issues with that.
Yes it can happen, but I do not believe it is common as made out.
I think the main issue is when 1st firing up an engine, for whatever reason, get a few backfires....and often the powervalve is not the right one for the engine vaccuum.
Once it is running the engine plays up, they figure out the correct power valve rating, check and change..runs fine and the old power valve is blamed as being blown.
In 30 yrs I have yet to come across aholley that has actually blown a power valve.
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Old Sep 4th, 09, 03:49 PM
greg1ontheedge greg1ontheedge is offline
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Default Re: What are symptoms of a blown power-valve?

Holley's website says it's ben using a check valve in their carbs since like 1982, so power valves don't blow.
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Old Sep 4th, 09, 04:21 PM
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Default Re: What are symptoms of a blown power-valve?

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Originally Posted by Steptoe View Post
Yes it can happen, but I do not believe it is common as made out.
I think the main issue is when 1st firing up an engine, for whatever reason, get a few backfires....and often the powervalve is not the right one for the engine vaccuum.
Once it is running the engine plays up, they figure out the correct power valve rating, check and change..runs fine and the old power valve is blamed as being blown.
In 30 yrs I have yet to come across aholley that has actually blown a power valve.
Shoulda met you in the early-mid 90s, then. I coulda showed you 3.

Now the very same carb is on the Camaro as we speak, but I keep the timing under close watch now.

I bought my 1850 Holley in mid '90-ish, just as they were starting to put the check ball thingy in all of them. Mine must be one of the last that doesn't have one.
No big deal.
Power valves are easy to change.
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Old Sep 4th, 09, 06:49 PM
jmartorana jmartorana is offline
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Default Re: What are symptoms of a blown power-valve?

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Originally Posted by Arch Stanton View Post
Shoulda met you in the early-mid 90s, then. I coulda showed you 3.

Now the very same carb is on the Camaro as we speak, but I keep the timing under close watch now.

I bought my 1850 Holley in mid '90-ish, just as they were starting to put the check ball thingy in all of them. Mine must be one of the last that doesn't have one.
No big deal.
Power valves are easy to change.
There is a kit to add the check valve to older Holleys
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  #8  
Old Sep 4th, 09, 06:51 PM
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Default Re: What are symptoms of a blown power-valve?

So the newer Holley's have a blow proof PV.
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Old Sep 4th, 09, 07:18 PM
fatblock fatblock is offline
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Default Re: What are symptoms of a blown power-valve?

Quote:
Originally Posted by 77thor View Post
It's a Holley... duh. I've had a few backfires through the carb and I have heard that Holley's can have issues with that.

How would I know if the power-valve is blown without taking it apart?
Unless the pv is externally referanced..it usually will require removal for testing.
A ruptured blown pv will allow raw fuel to enter the pv chamber and manifold vacuum will draw this raw fuel thru the baseplate and lead to an extremely rich condition that you can not lean out with curb idle mixture screws seated.This condition should be enough to warrant pv removal for testing.I do not like the taste of gasoline..so I use a handheld vacuum pump with a suction type cup over the suspect valve.This also gives you an hg # to verify pv opening/closing points.
Just to add..I believe the jury is still out regarding healthy pv.s open at idle rpm.By all means..the open pv will allow fuel into the main well..but this additional fuel still has to pass thru the fixed orifice commonly referred to as an idle feed restrictor(IFR) that feeds the curb idle mixture screws.
The added weight of fuel in the main well thru the pvcr may increase head pressure that works on the ifr and may show up on a mild stocker perhaps..combos vary.
I can only add that I tune with a wideband 02 sensor and can manipulate my pv,s externally with a hand held vac pump and the at idle a/f ratio does not change with the power valves open or closed.
Not saying this carved in stone..simply sharing my observations.
I select pv opening points on the road while viewing manifold vacuum #.s at different throttle angles vs engine load..not based on manifold vac #,s at curb idle speed.
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  #10  
Old Sep 4th, 09, 07:47 PM
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Default Re: What are symptoms of a blown power-valve?

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Originally Posted by fatblock View Post
Unless the pv is externally referanced..it usually will require removal for testing.
A ruptured blown pv will allow raw fuel to enter the pv chamber and manifold vacuum will draw this raw fuel thru the baseplate and lead to an extremely rich condition that you can not lean out with curb idle mixture screws seated.This condition should be enough to warrant pv removal for testing.I do not like the taste of gasoline..so I use a handheld vacuum pump with a suction type cup over the suspect valve.This also gives you an hg # to verify pv opening/closing points.
Just to add..I believe the jury is still out regarding healthy pv.s open at idle rpm.By all means..the open pv will allow fuel into the main well..but this additional fuel still has to pass thru the fixed orifice commonly referred to as an idle feed restrictor(IFR) that feeds the curb idle mixture screws.
The added weight of fuel in the main well thru the pvcr may increase head pressure that works on the ifr and may show up on a mild stocker perhaps..combos vary.
I can only add that I tune with a wideband 02 sensor and can manipulate my pv,s externally with a hand held vac pump and the at idle a/f ratio does not change with the power valves open or closed.
Not saying this carved in stone..simply sharing my observations.
I select pv opening points on the road while viewing manifold vacuum #.s at different throttle angles vs engine load..not based on manifold vac #,s at curb idle speed.
Hey George,
Tomorrow im going to pull apart my 4150 Holley and replace the 6.5 PV also to clean it out and re-set my T-slots because this thing likes to run very rich at idle and smokes like im dumping fuel down the carb, even with my wide band O2 at warm it idles fine 14.5 but when cold its hard to keep it running unless im running 1600rpms and then it starts to smoke. So im going to install a new PV, inspect clean, clean needle/seat, adjust T-slots and lower the float level just a little more. This is all coming from my conversation with Pro-Systems today.

George do you think all this time with my tunning issues that it could be a bad PV?
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Old Sep 4th, 09, 09:03 PM
fatblock fatblock is offline
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Default Re: What are symptoms of a blown power-valve?

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Originally Posted by Skeeter55 View Post
Hey George,
Tomorrow im going to pull apart my 4150 Holley and replace the 6.5 PV also to clean it out and re-set my T-slots because this thing likes to run very rich at idle and smokes like im dumping fuel down the carb, even with my wide band O2 at warm it idles fine 14.5 but when cold its hard to keep it running unless im running 1600rpms and then it starts to smoke. So im going to install a new PV, inspect clean, clean needle/seat, adjust T-slots and lower the float level just a little more. This is all coming from my conversation with Pro-Systems today.

George do you think all this time with my tunning issues that it could be a bad PV?
Skip..I highly doubt that you will correct your concerns with a new power valve unless it fails a vac test.Without being over the fender or riding shotgun with a vac gauge and viewing your real time a/f via your wide band..I could only half hazard a guess.
As for the smoking cold at 1600 rpm..is she black or blue?Hopefully more black then blue.Black can be corrected..but blue will only get worse with rich mixtures that fuel wash cylinders walls and compromize ring seal.
Get this sorted sooner than later.
Do I dare say.try a different known good carb.I will leave that up to you to decide.
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Old Sep 5th, 09, 08:34 AM
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Default Re: What are symptoms of a blown power-valve?

Quote:
Originally Posted by fatblock View Post
Skip..I highly doubt that you will correct your concerns with a new power valve unless it fails a vac test.Without being over the fender or riding shotgun with a vac gauge and viewing your real time a/f via your wide band..I could only half hazard a guess.
As for the smoking cold at 1600 rpm..is she black or blue?Hopefully more black then blue.Black can be corrected..but blue will only get worse with rich mixtures that fuel wash cylinders walls and compromize ring seal.
Get this sorted sooner than later.
Do I dare say.try a different known good carb.I will leave that up to you to decide.
George.... Its defiantly black and ive been on top of this from the very beginning. The first problem with my smoking issues were the PCV sucking oil (fixed that). Ive always check the oil for any signs of fuel smell and rubbing the oil between my fingers looking for the oil to fish eye (but nothing looks and smells good). I do understand about the fuel wash but its not that bad (YET)... I'm just anal and like motors to run clean and very responsive, it clear the plugs right up when i get it up to highway speeds as long as i don't set there idling and snapping the throttle (thats when it loads up then smokes) ...

I have a strong feeling its my float levels are still to high, but im going to blow the carb apart anyway. Hope i find something.

Thanks George.
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Old Sep 5th, 09, 08:40 AM
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Default Re: What are symptoms of a blown power-valve?

Sorry for high jacking this thread... I will see if i have a blown power valve and i think some symptoms are excessive fuel dumping down the ventures and very hard to tune with your fuel mixture screws as the blown power valve will take over with the idle circuit from the excessive fuel at idle.
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Old Sep 5th, 09, 02:54 PM
Steptoe Steptoe is offline
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Default Re: What are symptoms of a blown power-valve?

Before sorting what PV u need, you have to adjust the sec idle position so the mixture screws are in the middle of the factory spec...
Make sure the Accel pump has about 15 to 18/1000" at WOT
This will (should) put the the idle vac above the PV spec...then as described above road tested with in car vac gauge (at least) to determine the PV reqd...using a A/F gauge is not reqd, but it certainly confirms if you have got it right.
All of these steps are a basic must/std proceedure when dropping a new carb onto an engine

Once these are storted it is time to setup the dizzy curve.

The seach function in these forums pulls your answers real quick and saves ppl posting the same BS over and over yr after yr.
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Old Sep 5th, 09, 03:59 PM
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Default Re: What are symptoms of a blown power-valve?

Quote:
Originally Posted by Steptoe View Post
Before sorting what PV u need, you have to adjust the sec idle position so the mixture screws are in the middle of the factory spec...
Make sure the Accel pump has about 15 to 18/1000" at WOT
This will (should) put the the idle vac above the PV spec...then as described above road tested with in car vac gauge (at least) to determine the PV reqd...using a A/F gauge is not reqd, but it certainly confirms if you have got it right.
All of these steps are a basic must/std proceedure when dropping a new carb onto an engine

Once these are storted it is time to setup the dizzy curve.

The seach function in these forums pulls your answers real quick and saves ppl posting the same BS over and over yr after yr.
Steptoe... lol If it weren't for people like you and the TC gang we wouldn't be here. Because no matter how many times we ask these silly questions, its nice people like you who redirect use to put on our thinking caps again. So i just want to thank you ..
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