The city’s largest pension board is refusing to grant a disability pension to a 291-pound worker who developed asthma after the cleanup effort at Ground Zero, saying his weight was the chief cause of his illness. Emergency Medical Technician Michael Abramowitz — who transported body parts of victims to the morgue after 9/11 — was forced to retire in 2010 when FDNY doctors determined his asthma and psoriasis made him medically unfit for the job. He was 56 at the time. So like many others who worked at Ground Zero, Abramowitz applied for a disability pension. A doctor certified that his asthma is “related to 9/11-related dust exposure.” But the medical board of the New York City Employees’ Retirement System saw things differently and blamed his girth — not exposure to toxins — for his health problem, according to records obtained by The Post.