Hi
Ihave a 1991 Springer with stock carb on it. When running at about 30 mph it starts juddering and backfiring but when i open her up she runs like a dream.
Hope someone can help.

 

You might want to drop the float bowl on the carb and ck for junk in the carb. maybe consider and overhaul. Also check your intake manifold orings and replace.

 

Yeah, like mentor70 sez, and replace that POS carb with a S&S.

 

Downshift.