My '86 use to get 25mpg but after a carb rebuild (in 2002 because I couldn't pass emmissions), it now passes emmissions but I only get 20-21. It runs really rich when cold but I wouldn't think prolonged cold starts would cause a 20% drop over a tankful. Now I only get 300 miles per tankful

Any ideas what to look for? BTW, my compression in all 4 cylinders is still 140-150psi. Spark plugs look the right color.