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View Full Version : Power Valve in Holley 4150 Carburetor



Barry Eller
07-26-2008, 07:34 AM
What are the symptoms of a blown power valve diaphragm in a Holley 4150/850 CFM carb? I experienced an immediate rich running condition, backfires and fouled spark plugs.

ky-donzi
07-26-2008, 08:36 AM
That's sounds like one to me. They are pretty easy to remove and replace. If your carb is a newer one most have a power valve check valve that reduces the risk of one blowning. If not you might want to add the ckeck valve. I think Jeggs carries the kit

RickR
07-26-2008, 08:40 AM
Sounds like the right symptoms BUT before I took the carb apart I would check for moisture in the distributor, advance and timing.

Also (with due caution, especially eye protection) I would look down the carb at idle. If you see fuel dripping, spray some carb cleaner in the small brass bleed holes. If you still suspect they are clogged, try running a piece of wire fishing leader in the hole wo/being too aggressive.

If it is a new carb be prepared for a project. THE OE gaskets are a PITA.

BigGrizzly
07-26-2008, 09:05 AM
I am with Rick on this one. Be careful these symptoms occur for other reasons also. The power valves have a bad rep. For the wrong reasons. People have blamed them for their own incompetence. Remember tuning a carb is also selecting the right power valve.

Barry Eller
07-26-2008, 08:02 PM
If you take it apart, get the Barry Grant re-useable gaskets :)

I have a couple Holley kits on hand with the blue, reusable gaskets. I'll check the distributor cap for moisture, I usually lightly spray inside it with W-D 40 for preventive measures.

My alternator, that I just had rebuilt, dropped voltage shortly before the engine started this condition. I'm thinking that may have affected my MSD Ignition Module. As I understand it, MSD requires a full 12 volts to operate properly.

I'll know more tomorrow, as I will have some time to check a few things.

RickR
07-27-2008, 07:49 AM
Barry
I am running MSD also.
I have not had much luck with the caps after they have gotten "carbon tacked".

BUIZILLA
07-27-2008, 07:59 AM
Barry
I am running MSD also.
I have not had much luck with the caps after they have gotten "carbon tacked". there are a couple of us that carry spare MSD cap's as mandatory cargo... I keep two... one IN the boat and another in the truck stash...

BigGrizzly
07-27-2008, 09:17 AM
MSD needs voltage especially at idle. Mine doesn't like to idle below 12 volts-don't ask. WD40 not good in a cap especially the red MSD cap. I no longer use MSD caps but the blue point, they have brass conductors- always carry a spare.

Barry Eller
07-27-2008, 09:30 AM
10-4. I'll get two caps and rotor buttons.

My carb calls for power valve 125-65(22) which opening vacuum is 6.5 inches.

Does that sound about right for my application? I don't know what the (22) means after the part number?

I have Dave Emanuel's book, "Holley Carburetors;Super Tuning and Modifying".

Barry Eller
07-27-2008, 09:32 AM
MSD needs voltage especially at idle. Mine doesn't like to idle below 12 volts-don't ask. WD40 not good in a cap especially the red MSD cap. I no longer use MSD caps but the blue point, they have brass conductors- always carry a spare.

Will the "blue point" cap fit my MSD Pro Billet Distributor?

I have to get this worked out before the "Owners Rally" in FT. Walton! I'm looking forward to meeting you Grizz!

I need some Donzi stickers for Dan's Pantera!

BigGrizzly
07-27-2008, 09:42 AM
It should. At least you have a good book .

BUIZILLA
07-27-2008, 09:58 AM
I would use a 6.5 in the primary and a 4.5 in the secondary

but, that's just me..

smbarcelow
07-27-2008, 10:04 AM
I just replaced a blown power valve in mine. It was dumping fuel through at idle. The back of the boat is now black...still have to find an effective cleaner. She seems to run well now. Putting her back in today.

FYI, I have a 350 HP ZZ4 350 with a Holley 750 using a 6.5 primary power valve. No power valve in the secondary metering block. I suspect this is what came from the factory (GM Performance Parts, not Donzi). I have not yet measured vacuum at idle. Just picked up a gauge the other night.

Barry Eller
07-27-2008, 10:17 AM
I just replaced a blown power valve in mine. It was dumping fuel through at idle. The back of the boat is now black...still have to find an effective cleaner. She seems to run well now. Putting her back in today.


Bon Ami...never scratched, never will. GM recommends Bon Ami to clean automotive windshields that have hard water spots and windshield road film.
Just wax after using it on your gelcoat.

I'm thinking most of my engine problems are electrical, not a blown power valve. But I am going to clean my carb up anyway.

joseph m. hahnl
07-27-2008, 11:46 AM
Bon Ami...never scratched, never will. GM recommends Bon Ami to clean automotive windshields that have hard water spots and windshield road film.
Just wax after using it on your gelcoat.

I'm thinking most of my engine problems are electrical, not a blown power valve. But I am going to clean my carb up anyway.

Power valves are designed for enrichment when vacuum is lowest at idle.
That is in the idle circuit when the transfer slots are still in the path of the butterfly plates.
enrichment conditions can be caused by a faulty choke wire Or a sticking choke plate. Idle enrichment screws can back out. Power valves do not generally go unless there is a back fire Through the carburetor(during a lean condition). If there's an anti back fire check valve( I think modern Holly's have them built in) chances are unlikely that it is blown. It also would not generally effect a wide open throttle condition. As it most likely would be absorbed by a wide open venturi . The problem I have had with Holly and Webber's is debris in the float meter seat. allowing unatomized fuel to drip Through the trucks
Most importantly is the fuel pump diaphragm it may be ruptured allowing unatomized fuel to dribble in to the intake.You should definitely remove the spark arrestor and check the throat body for dripping or dribbling fuel.. This condition leads to hard starting and flooding. Which may not be a factor in your case.Also check the choke plate and make sure the choke is opening. If it were merely say a dead electric choke wire or a faulty or disconnected manual choke stove you can access this with out taking any thing off, other than the arrestor.At the same time you can adjust the idle screws and on Holly's I believe they allow you to take the float meter seat valve out of the fuel bowl with out removal of the carburetor and or the fuel bowl Also if the battery has a good charge it should run the ignition regardless of the alternator that is until the battery dies out.Hope that helps good luck