Power valve failure

[46woodie]

I have a 59A in my 46 Ford. Car runs excellent but when I'm done driving gas is seeping out of carb (stock Ford) between base and throttle body. Charlie has rebuilt this twice and it had a bad power valve when I sent it to him so this is 3rd valve gone bad. Have had to change oil couple times due to gas in it. Also have excellent fuel pump that Charlie rebuilt. Like I said,car runs incredible but leaks gas. What is the problem? Thanks!

[Russ/40]

This isn't going to help you much, but that is why I run a Stromberg. Never another power valve problem. The holly power valves must seal to the casting, or they will leak, even if the diaphragm is good. Take the top off the carb and fill the bowl with fuel. The power valve must be sealed and not leak down.

If you have a backfire, it may blow the power valve diaphragm.

[rotorwrench]

Charlie usually modifies for the late type valves to work since no one makes the old style. If an engine is running too lean, it will backfire through the carb. This canl cause the vacuum diaphragm to blow out. Modern fuels are hard on carbs too. Rubber parts don't hold up well.

My old Mercury uses the Holley 885 and they used a power valve set up similar to Stromberg in those. They can have problems with the extensive vacuum circuit for that type power valve due to poor sealing of the shroud parting surfaces but when they work, they work well.

[46woodie]

No backfiring and like I said it runs great. I'm sure Charlie did a good job tighteningthe power valve so Its has to be sealing ok but will double check. Thanks

[Ken Henry]

It could be percolating after heat soak. If you look down the throat of the carb after shutting off, you will see fuel dripping out the nozzle bars in this scenario. It tends to run out at the base of the carb near the throttle plates. Ken

[nbrskn]

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read her I think that the power valve can be pluged off/ Is this true ?

[ford38v8]

Originally Posted by nbrskn

read her I think that the power valve can be pluged off/ Is this true ?

I'm sure it can, but why would anyone want to? Maybe in a stationary engine?

[Ol' Ron]

Just curious, how often do you hear of a PV failure? Can't remember the last time I heerd of one???

[chap52]

I was running dual 94's and Charlie advised to block off pv's. So I purchased a couple of correct pv plugs from him and it ran wonderfully after that. Don't know why, it just did? Chap

[Ol' Ron]

I like to tune a street engine for economy, which would be too lean for WOT.

[my4dv8]

It probably does run fine without PVs ,until you stomp on the go pedal and it will likely fall on its face. Maybe you have masked the no PV with bigger jets?
A common solution is to stick to stock size jets and a PV with a lower value than stock so it opens at a later at lower vacuum.

[Charlie ny]

46,
Time to send the carb back again. I'm thinking the PV gasket face on the
bowl is not square with the PV threads....possibly creating a strain when tightening

the PV.....we'll get it done.....N/C
Charlie ny

[46woodie]

Thanks Charlie!! Better if you have a carb that you know works correctly and send that and I'll send this back. 3rd time taking this off and shipping, not only expensive but pain taking on and off. You do great work,car runs great, but have had to change oil few times also because of gas leaking through.Car Starts alright after fuel bowl refills but drains into crankcase if car sits overnight. Going to run into major problems here. Thank you again

[Charlie ny]

46,
Check your PM's
Charlie ny

[rotorwrench]

Back in the days of round aircraft engines, they used fuel dilution in the oil tank to make the oil thin enough to flow through the engine for cold weather starting. The oil tanks had a tank within a tank (down in bottom center) to do this so they were pretty special tanks. After the engine was warmed up sufficiently, the dilution was no longer necessary and system was shut down. During the flight, the fuel would quickly evaporate out of the oil since only a part of it was affected. Some big round motors still have systems like this but are not used in semi-arctic conditions much anymore. These systems necessitated changing the oil by proper schedule which is about every 25-hours. most engines now days have spin on filters so that the interval can go up to 50-hours between changes. With dilution, an operator has to remain on the 25-hour schedule. This system was better than draining the oil after shut down then heating it on a stove and pouring it back in before a flight. That was even more work. Aircraft operators had it rough back in the day operating in northern countries anywhere near the arctic circle.

[Charlie ny]

46,
Your address please

Charlie ny

[46woodie]

396 21st st se
Cedar Rapids
Iowa,52403
Thank you,Richard C

[Daves55Sedan]

Couple weeks ago, I ran a '55 Ford car 75 miles at about 70mph and when I got to town, and began running at lower speed limits, I had a hard time keeping the engine idling well. I shut it off, popped the oil-bath air cleaner off and looked down the throat of the carb (Ford EBU 2-bbl with 1" venturi's). Gas was pouring down onto the butterflies. No doubt, power valve was stuck open.
The carb comes off easy on a Ford 292 Y-block and I had it in my hands in 15 minutes. Took out the power valve (located between main body and valve body). When I tried to push the plunger back to the closed position using my thumb, it didn't even want to move. Slowly working it back and forth, using a lot of pressure with my thumb, I was able to free it up so that it would move to the open and closed positions, but not without force. And certainly, there is no way 6.5 inches Hg of vacuum was going to move this thing. That power valve came from a Daytona parts kit, probably about 2 yrs ago. The car is run daily.
In order to get back home, I installed my spare EBU carb (which also had a Daytona Parts kit in it). When I got home, I looked and noticed that this power valve was leaking also, but a little less than my other carb. Temperature was in the mid nineties that day.
I think that the hidden O-ring inside the power valve that is supposed to seal when there is less than 6" Hg vacuum must be expanding due to being in contact with the gasoline. If the rubber is expanding, that would explain why it was so hard to move the plunger by hand. The rubber would be crushed against the I.D. of the valve passage bore. These are supposed to have ethanol-safe rubber parts.

[Daves55Sedan]

I've heard a lot of people complain in the past about running errands and stopping somewhere, then when they come back out to start the car to go to the next place, the car won't start.
First thing I check is to see if the power valve is struck open, by looking down the carb throat to see gas pouring down onto the butterflies. This is instant flooding.
You can blow into the carb to clear some of it and wait a while, but then get a empty tuna can with a spout bent into it. Pour it half full of gas and carefully pour that gas down the little air tube that goes into the float bowl. (Some older carbs don't have that tube so I don't know how you would prime the carb on those).
Now you need to watch and see if the gas you are pouring into the float bowl isn't just pouring down the throat. If so stop. But if the power valve is holding closed you might be able to get the car started, then gun the engine a few times might un-stick the power valve and allow it to close.

[Charlie ny]

In conversations with Richard he asked me for a different 94 which I supplied him N/C.
No leaks on this carb per Richard. The original 94 was returned to me once the replace-
ment proved itself. This was a while back and no issues since then that I'm aware of.
This is a June posting.

Charlie ny