I have the same problem. It appears to be the rocker cover gasket. Am going to replace it and see what happens. Hope this helps.
311777
YES, IF THE MODEL # 311777 TYPE 0148-E1 CODE 990604ZE IS WHAT YOU HAVE. I HAVE ONE.
I need the valve settings for a 17 hr. Briggs mod. 311777 type 0131-e1 code 980521zd THANKS DENNIS