Fair Weather Friend
 

I'm in L.A. It's been cold and damp (by Calif. standards anyway)
Today, tho it was drier and went up into the 60's. I noticed a remarkable difference in the performance of my 74 450 SEL.
When it is colder and damper, it misses a bit and is down on power. But as it heats up and gets less humid, or drier, there is alot more pep and pickup. Since the timing elements don't change
(points, plugs, timing etc), what does? Is it related to lean/rich
fuel mixture. What are the different ways to lean or richen the mix?
I've heard that one way is to turn the allen screw on the small cylinder near the left driver's inner fender (to the rear of the coil)
Which way to turn for lean or rich?
Are there other things I'm missing that affect performance under
cold-humid or hot-dry conditions?

Cold moist causes problems with trigger points and ignition points along with leaking secondary ignition (plug wires and plug wire ends).

I would advise against adjusting the MAP sensor without a lot of experience or an exhaust gas analyzer.