$400 - 500 a week income? I'm hoping you really meant income, not gross sales. however even for 40 accounts that number seems very low for income after all expenses.
in order to determine the possible profitability we would need to know equipment included (age/hours,) vehicle?, size of accounts, etc.
Edit, Welcome to Lawnsite too, wear boots, because it gets deep in here.
Efficiency = Profit