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Err, white smoke is usually steam, which would be very bad. Gasoline smoke is black, oil smoke is blue, water 'smoke' is white.

I'd say for testing purposes just disconnect the manifold from the exhaust pipe and then you can see if you are having backpressure issues. It'll be loud, but if it runs good then you know it's exhaust backpressure. Since you are in CA with a '81, you have to have a cat. And I think it's illegal for someone to sell you a used one, i.e. you can't buy them at Pick-Your-Part I think. I'm rooting for you that it's not the catalytic converter. How do the plugs look during all this?

White smoke back through the carb can be fuel vapour (unburnt, so not smoke). CAN be... steam is definitely very very bad.

On the EGR valve piece mentioned in the beginning of this thread...
Don't take it out. I can't stress that enough. I'm sure everyone knows that regular pump gas is usually only good to about 8:1 compression, right? Well, the EGR valve is like an octane booster. Higher octane numbers mean slower burn rates, and higher numbers are less likely to ping. SO, the EGR valve is there to keep you from pinging your engine into a pile of junk. The exhaust gasses are already burnt, so they will slow the rate of burn down considerably, just like the lead in the good ol' gas you guys used to be able to get (I'm only 18, and wouldn't know about the beauty of running 13:1 on pump gas...)
lol, octane rating can be also be raised by adding small amounts of diesel to your tank as you're filling it.

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1980 4X4 LUV daily driver, as stock as can be.