First, if you are going to separate the carburetor from the fuel tank, you need to read the Briggs manual.
Second, for all of the side valve engines AFAIK, Briggs specifies SAE30 engine oil, meeting American Petroleum Institute standards (SF, SG, SH, etc. - they keep bringing out new ones). Briggs says you can use, say, SAE 20W-30, but you should expect to burn quite a bit more of it than you would with straight SAE30. Outdoorking members seem to have verified the truth of this warning.
