MG Car Repair: 76 Midget backfire, emission control, check valve

Question
I have a '76 Midget that has a backfire whenever I shift between 2nd & 3rd and 3rd & 4th. This only happens when I up shift.  I bought the car a month ago and the first thing I did was change the plugs and air filter. Other than the backfire the car runs great. Any suggestions?

Answer
Hi Gary,
Many things can cause a backfire between shifts. First and most likely is a leak in the exhaust system (usually somewhere in the front)
Some emission control items could be the cause also. EGR valve or the check valve. Any thing that can allow air to enter the exhaust system can cause a backfire.
Howard