Re: 91 Mercury 75 Hp Air/fuel Mixture @@@
Start out at 1 ? ( manual specs) turn open and then go out until it starts hesitating and in till it hesitates , find your peek points.. And adjust accordingly..

The blue bottle is a oil tank reservoir and contains your 2 cycle oil.. If I was you I would change the oil out and use quicksilver? works great.. Assuming that you never have ran this motor.. It might be old ( the oil)

hope this helps