yesterday was driving in 3rd -- it b(ar)fed decelerating at 30 mph or faster
put it into drive and b(ar)fing quit -- never b(ar)fs until decelerating ~55

good sparks, cap, rotor, wires, right engine operating temp, 0TDC timing, no known vacuum leaks, good choke, >1 yr old o2 sensor
any ideas in what makes difference between 3rd & drive deceleration?

 

you mean the popping coming out of the exhaust during decel? If so that is normal and all free flowing exhausts do this. Higher rpms in 3rd than 4th would be why it would do it at a lower mph. Totally normal though.

 

Thanks that's one off the whatisit? list

 

THe difference between accelerating and letting off in 3rd and drive, is that in drive, the engine nearly freewheels when you let off the gas, because you are in OD. In 3rd, you will have engine braking, making the car pop more through the exhaust as it winds down w/ an overrich exhaust condition for a brief second.