How to Adjust a Harley CV Carburetor
by Gabriel Scofield
Harley-Davidson Motor Co. used the constant velocity (CV) carburetor in the 1988 Sportsters, 1990 Big Twins (EVO and TC88) until 2006. Since then, all Harley-Davidson motorcycles make use of fuel injection. The CV carburetor may show signs of needing to be tuned. These signs include a drastic decrease in fuel economy, black smoke appearing from the exhaust, sluggish acceleration, the engine spitting back through the carburetor, or hesitating upon acceleration. A low-speed circuit adjustment to the carburetor can be made in minimal time
.
Step 1
Check spark plug for light-brown glassy deposits which may be accompanied by cracks in the insulator or erosion of the electrode, which indicates a lean air-fuel mixture. Dry, fluffy or sooty black deposits indicate a rich carburetor air-fuel mixture.
Step 2
Locate the idle mixture screw on the bottom outlet side of the carburetor, in a passageway next to the float bowl. Turning the idle mixture screw in, or clockwise, will lean the idle mixture and turning it out, or counterclockwise, will enrich it.
Step 3
Drill out the metal plug covering the idle mixture screw. Do not drill too far into the plug; wrap the drill bit with tape or string to prevent you from drilling too far and damaging the screw.
Step 4
Pry out the plug with a small pick.
Step 5
Turn the idle mixture screw in (clockwise) until it stops. Do not over-tighten the idle mixture screw. Damage to the screw and its seat may result.
Step 6
Turn idle mixture screw two turns out (counterclockwise) to an idle speed of 1,000 rpm.
Step 7
Adjust the screw 1/2 turn at a time. After each adjustment, reset the idle speed to 1,000 rpm. The maximum adjustment range is 1/2 to 3-1/2 turns.
References
Tips
- When adjusting the idle mixture screw, make only small adjustments. Stick with the 1/2 to 1/4 turn rule. Often the smallest adjustment is all that is needed.
Things You'll Need
- Household drill
- 7/64-inch to 1/8-inch drill bit
- Small pick
- Small flat head screw driver
- Carburetor cleaner
Warnings
- These procedures may reduce or void any limited warranty coverage.
Writer Bio
Gabriel Scofield started writing in 2003 for motorcycle dealership websites. He graduated from the Motorcycle Mechanics Institute with a certificate in Early & Late Model Harley-Davidson. He since has reached the level of Harley-Davidson Master Technician.
