Is it possible my 86 Accord got 40 miles a gallon ..Today they say 29?

two things affected the gas mileage in the last 20 years: the advent of fuel injection that was necessary to minimize vehicle emiissions and EPA ratings system changes.

the older hondas were carbureted and got high mileage. to meet the emissions requirements carburetors had to go by the wayside and were replaced with fuel injection that gives the ability to more tightely control emissions. Fuel ecomomy was reduced as a result of the additional emissions equipment and the controls on the engine that are necessary to achieve those standards.

the second change was the EPA formula for calculating MPG changed in 2007 and knocked everything down to more realistic numbers. The Toyota Prius is an example where the MPG rating on that car fell by about 10 mpg in 2007 yet the car was unchanged mechanically and technically from th previous year.

also, keep in mind that today's accord is a much bigger car and heavier than your 86. the comprable sized car to the 1986 is the civic which is almost identical in wheel base and weight to the 1986 accord.