1986 90hp.lately hard to start when cold.seems like there is a fine line between getting enough fuel to start & flooding.new plugs,fresh fuel (premium),120 lb all cylinders,good spark.sometimes takes 15 to 20 attempts to start.enrichment valve appears to be working properly.what is the proper procedure in using the enrichment valve to start a cold engine(time valve should be energized)?been running this engine about 10 years & never had this problem.