power valve

What's the power valve do?

According to the service manual if you hook a vacuum pump up to the power valve line and apply a vacuum you should hear a clicking.
I did this last week, and my memory may be wrong, but I think all I got was a sucking sound, and eventually gas came in through the line. It was either that one, or one of the other vacuum connections along the top/back of the carb.
Can anyone confirm if this is normal behavior or not?
But if power valve wasn't working right, what would be the likely symptoms? I searched google, and this forum, and I couldn't really find what the valve does.

--Peter

What you did was connect the vacuum pump to the Air correction jet... either letter B or letter C

what you need to do is look for #14... that is the hose at tha back of the top hat that is closest to the fuel line to the carb...

if you still get fuel then your vacuum lines were not put in the right places

the #14 port on the carb actually goes thru an internal passage that should have no access to fuel even if there is a leaky top hat gasket which is one way fuel goes places it shouldn't... the port feeds to a valve that lifts the rod off the actual powervalve which closes the valve from feeding more fuel to the barrels... as manifold vacuum drops the rod, pressed by the spring that is around it... hits the powervalve and opens it up, giving more fuel... manifold vacuum drops as you increase throttle.

I checked the power valve line again today. When I apply a vacuum to the #14 line, it doesn't hold the vacuum, like not at all.
And yet if I left the vacuum line open, the engine clearly stumbled, but reconnecting the line caused the engine to run better. It was hard to tell if there was a difference between when I disconnected, and plugged the line, versus when I had the line connected. It seemed like it was just a hair smoother when the line was disconnected and plugged.

I bought a bunch of vacuum hose...when I get some free time I plan to replace everything I can get my hands on. It looks like there are a few lines that run under the intake manifold/under the carb...those will be a challenge.

lines under the intake manifold may be the coolant hose... be careful when messing with that... and or removing the carb... since a leak would cause coolant to flow into the intake and kill the motor.

there is actually only one hose that runs from the back base of the carb and goes under the intake manifold... that is the coolant one... it's a different size then the hoses next to it.

Also you may be Automatic correct? If you are you probably are seeing the TV cable going under the manifold.

if the power valve did'nt work the car would drive as if you have a a 3cy engine, it would be real slow.
try this.
where the valve is located take a vacuum line that's connected with-in it.
then find a vacuum line, then attach it, the engine should rev to 3,500 rpm's.
then release it , the rpm's should go down.

I'm a bit confused with your directions...

Quote:

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Originally Posted by A20A1

I'm a bit confused with your directions...

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Me too.

The car is a 5 speed. Thanks for the tips about the coolant lines.

okay, you have vacuum secondary right?
where the line leave's from the valve to a 3 way joint line, dissconnect then find a vacuum line that has constant vacuum.
then join the 2 line's together , the rpm's should go up to 3,500rpm's.
if it does the secondary is fine.

Did you apply vacuum to the carburetor or to the vacuum line?
You apply vacuum to the carburetor directly... or to the diaphragm you are testing.

When you disconnect a vacuum line you should always plug the line... sometimes you should plug the port on the carb too... but usually you only need to plug the line.

Vacuum Secondary and Power valve are two different things... or are you suggesting useing line #14 as the vacuum source to see if it is pulling vacuum?

I believe vacuum pumps have a gauge, so all he needs to do is disconnect line #14 from the carb and connect it to the gauge to test vacuum...

then plug line #14 and connect the hand held pump to the port on the carb to test the valve.

there is a small bleed hole in the valve... I'm not quite sure if thats why you are not holding vacuum...

i disconnected line #14, and connected my vacuum pump/guage. I got something like 21-22 in.Hg
Then I connected the pump to the carb port, and plugged the #14 hose, and applied a vacuum, and the vacuum wouldn't hold. The service manual says that's a problem. But I'm curious if anyone else has tried it.

that sucks... the powervalve isn't readibly fixable... it's sort of stammped into the carb, very hard to remove and isn't a part that is included in the rebuild kit... so you need to replace the whole top hat if it is indeed leaking. (Might want to get the whole carb)

pluging #14 will get rid of your vacuum leak but then the powervalve itself will always be on and you'll be wasting gas when not driving the car under heavy throttle...

what you could try is removeing the top hat and see if the rod istelf is stuck in the down position... even with the spring on it sometimes that rod can get stuck... so just gently push on the rod and make sure the rod moves in and out of the hole.

If you're absolutely want to try and fix it yourself you,ll need a dremel and a small grindind bit... with the grinder remove the indented aluminum areas surrounding the rod... it will look like cross-hairs... there are 4 indentations... with those gone the rod and valve that operates the rod should slide out... replacing the o-rings that go on the valve is something you'll have to figure out, I never tried to go any further then taking the valve out.

oh damn, . . . i forgot thier's something inside the carb i'm sorry man, i thought you were talking abot the secondary vale thingy itself.

Well, I've got the throttle stop screw cranked up a little, so the car runs, and it's been two weeks since this whole stalling problem started.
I'll try and remove the top hat this weekend (it's just like 5 screws, and then the thing should pull off, right?) and see what's up.

But what purpose does the power valve serve?

There's also a power valve control solenoid, too, right? I'll look into that.

I've only gone from about 32mpg to 28mpg. Considering the cost of a new carb, and my car has 156K miles, I might just learn to live with it.

Where do you live?
Only some had power valve control solenoids... if you live in the US you don't have one.

the powervalve adds more fuel when the engine demand is high. usually more demand the less vacuum... the less vacuum the more the rod drops because of the spring and the valve opens.

I live in the US. Boston to be specific. I'll do some troubleshooting on the power valve this weekend and see what's up.
Thanks for all the info Mike, you truly are a 3G genius.
It is amazing to me how much info this forum has on the 3G, and how little info I can find on the rest of the internet.

--Peter

Yesterday I removed the vacuum line from the power valve, and plugged the port and the vacuum line.
The idle increased slightly, but once I put the throttle stop screw back to where it was originally, the car still stalled.
So I'm not completely sure it's the power valve

Today I took the top hat off. If I apply a vacuum pump to the power valve, it doesn't hold the vacuum. If I press the rod up, and then apply the vacuum, it'll stay up, and hold the vacuum. There is a small hole that goes into the primary venturi channel, and this is where the air is escaping. If I put my finger over this hole, and apply a vacuum, the rod goes up and stays up.

Isn't this how the thing is supposed to work? If there wasn't an air bleed valve then when the vacuum dropped under heavy throttle, the rod wouldn't fall, because there would still be enough vacuum.

Mike, have you played with the power valve using a vacuum pump to see exactly how it is supposed to work?

Also, what is the carb supposed to sound like? Because when the car is running I can hear a hissing sound, and i'm 100% sure it is coming from down in the primary venturi. Maybe this is the vacuum from the power valve bleeder hold, maybe it's something else. I'd expect to be able to hear air in the venturi, since air is being sucked down into it, but I'm not sure if this sound is normal.

thanks.

--Peter

The hole is in the top hat...in the opening for the primary barrel.
interesting that that is your problem... thats what i was thinking and that why I asked you to push the rod up manually a few times to make sure the rod wasn't getting stuck, but covering the hole to make the valve more isn't normal... it should move when vacuum is applied. I'm pretty sure the bleed is there so the spring can lower the rod faster then if it operated like a diaphragm with no bleed.

Quote:

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Originally Posted by A20A1

what you could try is removeing the top hat and see if the rod istelf is stuck in the down position... even with the spring on it sometimes that rod can get stuck... so just gently push on the rod and make sure the rod moves in and out of the hole.

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anyways glad you found the leak... you can try and plug the bleeder hole and the powervalve should still work fine... but then you may need to have a heavier spring operating the valve... I'm really not sure.

usually a hiss is normal... but your hiss and my hiss are two different things so it's hard to say.

Well, I'm not sure the power valve is the entire problem. Since I capped off the valve, and I still got the hiss, and the car didn't run like it used to. Even when I plugged the hole, and used the vacuum pump to retract the rod it still didn't run like it used to. And of course things got worse since I removed and reinstalled the top hat. The old gasket is probably leaking.
So I was leaning towards a rebuild, but since the power valve isn't part of the rebuild, I should probably just replace the carb.
Should I get a new, used or rebuilt carb? Where is a good place to buy one? Preferably somwhere on the internet. I'd like to spend under $200 if possible.
I don't know any local junkyards.

Thanks
--Peter

just get a new hat, for now.
the hissing is normal IF coming from the barrel(s).
but like a20a1 said, less vacuum the more gas the power valve dump's into the barrel.
i know some of the guy's here are selling a carb.