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post #1 of (permalink) Old 08-13-2012, 04:08 PM Thread Starter
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Smile Carburetion problem solved

Finally I got to the bottom of the intermittent carburetion problem. At idle, sometimes it would be fine, sometimes grossly lean and rough. I had the intake manifold milled flat and replaced the gaskets, which needed to be done anyway, but was not a cure. Then I rebuilt the carb, which also needed doing. That wasn't a cure either, but at least it was cheap.

This morning it was idling rough at an 18:1 air/fuel ratio. I clamped Vice Grips onto the vacuum hose from the PCV valve and it went to 15:1 and the idle smoothed out. Took off the Vice Grips and it went back to the rough idle and 18:1 mix. I shot carb cleaner through the valve and went for a spin. It did fine for a dozen miles, but when I was almost home it messed up again. New PCV valve on order.

But seriously, thirty four years and the valve goes intermittent? Sheesh! They don't make 'em like they used to.

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post #2 of (permalink) Old 08-14-2012, 09:15 AM
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Humm... there's a saying for that: "Too soon old... Too late smart.
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post #3 of (permalink) Old 08-14-2012, 10:09 AM Thread Starter
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I knew I could count on someone to say that.

The real shocker is that there isn't a PCV valve in stock anywhere close. My buddy is getting one from Iowa or some other far away place. If this one doesn't last another thirty four years I may have to make a road draft tube. Remember those?

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post #4 of (permalink) Old 08-14-2012, 10:25 AM
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I've never looked at the specs for a PVC, but I imagine there are a bizillion configurations that really do the same thing.. at the same PSI to open the valve. Now all I have to do is find out that value.
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post #5 of (permalink) Old 08-14-2012, 05:30 PM Thread Starter
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I've not taken this one apart, but it apparently has no spring, but instead just lifts a metal ball to close off the flow. When the vacuum is high enough to lift the ball, the valve closes, so it will only work in a vertical position.

In my particular case I suspect the ball has deposits that keep it from closing completely when it rises in a certain orientation. Many PCV valves I've seen have a spring that serves the function that gravity provides on this one. It's a pretty robust design, having lasted all this time, and I suspect it would be good for another hundred thousand miles if I just soaked it in something that would eat the deposits off it. In fact, I think I'll try some things to see what works, and then keep it as a spare.

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