It's paying for all your expenses (mortgage, insurance, taxes) and then setting aside an additional percent (usually around 50% of the rent) to cover future maintenance, capital expenditures, vacancy, property management, etc.If you took 50% of your rent for expenses, that would leave you $1,200 to cover the mortgage and insurance.

Clearly something is not working for it to be on the market for so long and the numbers are most often the culprit especially in the slow season when landlords try to be more competitive in order to fill vacancies.

Add about 30% from $1700 of property management, capital expenditure reserves, and vacancy expense, now you are at about $1930 in total expenses per month, net cash flow of -$200.You can decide to manage your self and then you are break even.It not a bad deal but you should ask yourself is there a place you can get a better return on your investment.

I get a 7.7% Cap with 5% vacancy and $200 accounting fee. 

I put a 20% vacancy factor in because of turnover.  

The new supply over last couple years has increased vacancy rates and from a recent market report will continue throughout this year. 

Your rental income might come in every month - a check from your tenants - but your expenses might be "lumpy" in that you'll have a major repair once a year, a month of vacancy after tenants leave, etc. 

Great opportunities for AirBnB to cover vacancy periods there.

Anthony and Greg gave good info.Freddie Mac or Fannie Mae agency loan options depend on the property's economic vacancy at the time of loan application submission, physical occupancy for last 90 days, submarket, and your net worth and liquidity cash position. 

Also, statistically speaking, lower-income housing can have higher vacancy and higher turn costs due to damage and evictions.