what causes engine to misfire and backfire losing power
A bad fuel pump, or the carburetor is flooding out.
1973 last of the point and condenser ignition system if it hasn't already been modded. Replace the point and condenser, check the breaker plate for any side to side movement, if it has some replace the breaker plate, reset point gap, start engine and check the dwell.
If the above doesn't work, run a compression test to see if there is a problem with the timing chain and cam timing.
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