To get the adjustment right, you need a CIS fuel pressure gauge to measure the cold control pressure that the WUR regulates. But if you don't, and everything else is up to snuff, you can try pulling the brass plug upwards very slightly by tightening the nut down against the WUR body by a 1/4 turn or so. This will lean out the cold fuel mixture.

If the car starts to hesitate or stumble when cold, you turned it too far. Back the nut off slightly and tap the plug back down. I've seen a definite gas mileage improvement using this adjustment since mine was running way rich, though I think it only affects fuel consumption during warm-up.

PS - Do not under any circumstances turn the threaded screw that goes down into the brass plug, only turn the nut.

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma