If it has an older metal gas tank like mine has, it will accumulate rust and pass the rust to carb. I soaked my tank with muriatic acid, rinsed thoroughly with baking soda/water but still accumulated rust and passed rust to carb. You might be able to find an after market plastic tank.
I can't remember if I am supposed to use a tachometer to set the "H" carburetor adjustment or just adjust "H" to max high speed before it starts to bog down. Any recommendations?