Sensation mower

I bought this a couple of years ago, I’ve not done too much with it but I’d like to know how much oil to put in the engine? it doesn’t have a dipstick it’s a cap with two prongs sticking up and I think I may have overfilled it as there is a bit of black oily smoke when it runs. It has the original engine - Briggs and Stratton 92902 - 1823 - 01, I believe the sensation model is 11J3. Thanks