Anch' io da piccolo avevo prima il triciclo..poi la diciclettina con le 2 ruote dietro..poi me le hanno tolte è ho imparato ad andare in bicicletta..ho avuto molte motociclette .( 13) ma nessuna con le rotelline !!🤣🤣
First thing I would check is the A arms if one is to low to the left in relation to the rear tire it will turn right and then vise versa. I have built several wheelie machines and sell them. Also I would try to align your rear tire but the rear tire is usually secondary and doesn't have as much of an effect.