Ok, I have a 52 plymouth flathead 6 that starts as soon as you turn the key and just purs like a kitten. When you rev it up is sounds like its missing a little but nothing real noticeable. However, put it in gear and it has a hard time (rough running as hell) getting going, but once going it runs smooth down the road in all three gears. At 50 mph it drives perfect, it just has a spot in the acceleration where it runs rougher than hell and backfires to if you keep on it. I cleaned (not rebuilt) the carb on it thinking it just need the carb redone and that cleaning it real good may be good enough but it made zero diff. I am a body and paint guy so motors are my weakness but I am trying to learn this stuff since my dad lives to far away and don't have time to drive down here every time i need engine troubleshooting...and he won't be here forever so I need to learn this mechanical part of hot rodding. Any help is appreciated.