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Hi all, i know my truck is an 87 but mechanically it might as well be an 86 😁 I’ve been having issues since I replaced the power valve in my carb. I tossed the old one and I don’t think there is way to get it back. Here’s the issue. And it is random! It is flooding with gas on partial throttle under load above 2k rpms. What’s the part number or specific type I need to get the power valve closest to original?
also are they adjustable?
Thanks so much!!
What do you mean by "flooding"? A power valve can't add enough fuel to cause the carb to flood. It can add enough to cause a little bit of black smoke, but that is at idle only.
I’m not sure what the number is on it. It came in a kit from Napa.
Im not 100% sure it is the power valve but it is dumping too much fuel in the intake so it will bog down. And it only happens sometimes. It has been a headache
Most of the kits include a 6.5" power valve. This is not a problem. The power valve simply determines at what point extra fuel is provided due to load requirements, not how much. Something else is going on here.
But it's important not to make changes to a carburetor like that, in general. If you don't know what was installed before, and don't know what is installed now, that makes it kinda tough.
Is the engine modified for performance, or closer to stock?
Most of the kits include a 6.5" power valve. This is not a problem. The power valve simply determines at what point extra fuel is provided due to load requirements, not how much. Something else is going on here.
But it's important not to make changes to a carburetor like that, in general. If you don't know what was installed before, and don't know what is installed now, that makes it kinda tough.
Is the engine modified for performance, or closer to stock?
Yeah I know I goofed. I figured it was in the kit so I could replace it. Live and learn I guess. I’m pretty sure it’s stock other than an Edelbrock performer 460 intake
Without being able to look at it best guess is still believe it's something else, carburetor bowl fuel height, ignition timing is off, carburetor idle mixture needs adjustment, vacuum leak etc. What other maintenance did you perform? It's not the power valve...
Without being able to look at it best guess is still believe it's something else, fuel height, ignition timing is off, carburetor needs adjustment etc. What other maintenance did you perform? It's not the power valve.
Just gaskets on the carb. The timing is right. All new ignition system
What do you mean by "flooding"? A power valve can't add enough fuel to cause the carb to flood. It can add enough to cause a little bit of black smoke, but that is at idle only.
Uh no.
If the power valve value is to high it will open too soon and over fuel the engine causing bogging and copious amounts of black smoke out the tail pipe. The Power circuit by-passes the main jets and fuels the emulsion circuit and booster directly from the fuel bowl when the valve opens. See below diagram.
Sounds like your power valve is to high a value or it is leaking ?
If the power valve value is to high it will open too soon and over fuel the engine causing bogging and copious amounts of black smoke out the tail pipe. The Power circuit by-passes the main jets and fuels the emulsion circuit and booster directly from the fuel bowl when the valve opens. See below diagram.
Sounds like your power valve is to high a value or it is leaking ?
As previously stated 6.5" is a good safe bet.
Thanks for the info I ordered the 125-65 Holley single stage standard flow power valve. Will update once it is installed
I have had several Ford vehicles that have had blown power valves, and they have run fine except for running very rich at idle.
I will admit if somehow the power valve was improperly installed or the gasket was leaking, it may admit more fuel, maybe enough to cause problems. But it would be a constant problem. I don't see a power valve coming on at the incorrect time causing "flooding".
My theory is the the fuel system has dirt in it, the carb is trying to pass small bits of dirt through the needle and seat, and once in awhile it's getting stuck in there and overflowing the fuel bowl into the engine.
I have had several Ford vehicles that have had blown power valves, and they have run fine except for running very rich at idle.
I will admit if somehow the power valve was improperly installed or the gasket was leaking, it may admit more fuel, maybe enough to cause problems. But it would be a constant problem. I don't see a power valve coming on at the incorrect time causing "flooding".
My theory is the the fuel system has dirt in it, the carb is trying to pass small bits of dirt through the needle and seat, and once in awhile it's getting stuck in there and overflowing the fuel bowl into the engine.
A blown powervalve makes a difference at idle,as it introduces fuel directly in to the intake, the diaphragm seals the fuel from the fuel bowl lose the diaphragm and it dumps extra fuel in to the intake.
A PV that has a to high a value will open to soon introducing extra fuel in to the main circuit before the engine can use it this usually results in bogging as you suddenly get a big rush of extra fuel bogging the engine befre it can use it..
Unlike a PV that has failed where the extra fuel is already there and will result in reduced performance from idle till when the PV was supposed to open.
That is how the PV can mess things up cause bogging and over fueling.
Checking for debris in the needle and seat may be worth doing, but you would have to have a constant supply of crud to do this then only happening when on partial throttle under load above 2k rpm. That is too consistent for it to be dirt. And the symptoms he is experiencing are exactly the same as a to high a value power valve.
If it were mine I would start the truck on level ground, pull the sight plug(s) and set the float level(s) one at a time of course.
Those power valves are somewhat robust. It's not like you had to replace them with every backfire. Lots of times people ran too much duration and they wouldn't stay shut.
I would also look to see if you actually have a check ball and correct spring that your secondaries arent flopping open.
01-20-2018, 01:29 AM
