Your Harley's engine street performance is usually the best way to tune the carburetor. Due to different grades of gasoline, gasoline additives, altitudes and riding styles plug readings may differ from engine to engine. After bike has warmed up and idle speed has been set, it is now time for an initial test ride. While riding the motorcycle pay close attention to the off idle to 1/3 throttle position. In this range, watch and listen for the following:
a. Flat spot off idle
b. Lag in acceleration
c. Backfiring on deceleration.
These problems can be remedied by richening the needle position. NOTE: Before making adjustments for this condition, check for intake and exhaust leaks. These leaks have similar symptoms.
Lazy accelerationb. Poor mileagec. Surge at low speedsd. Poor fuel economy
These problems can be remedied by leaning the needle position. Gasoline is very flammable.
DO NOT work on any carburetor while smoking or around an open flame. It is also strongly recommended that any procedure pertaining to gasoline be performed in a well-ventilated area, as the vapors can be harmful.