Would changing transmission effect my carb settings?

[lutzy]

I changed from a TH400 to a 5 speed and the car started to backfire when letting off gas.. Would this have anything to do with changing tranny's?

[Vegas69]

It very well could. You are going to have more engine braking with a greater amount of gears. Does having it in a higher gear improve the situation? That would be my first test.

[GregWeld]

Did you remember to plug the vacuum port your TH400 WAS plugged into?