The screw is right hand thread and when screwed all the way in stops the flow of fuel. So, looking at it from the side of the Jeep, with the engine at operating temperature, you screw it clockwise (inward) until the Jeep starts to stumble, then start backing out very slowly until you reach the highest RPM. Once you start making it too rich, the RPMs will actually drop slightly.
Ideally, you would have a tachometer hooked up, but with the waterproof ignition that gets a little complicated. There are also timing lights with digital RPM gauges on them, but it is actually getting harder to buy a timing light these days.
It was not a modification to have the M151 type aircleaner...that was standard on the CDN2 and CDN3 Jeeps. I have never heard of the plastic "horsehair" coming apart....leave it alone and you will be fine.
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