Carburetor Adjustment - Harley VL - Rider's Manual

Adjusting the Carburetor on a VL

This how-to article applies to 1930-1936 Harley Davidson V series motorcycles and originally appeared in the rider's manual

Don't continually tamper with the carburetor adjustment. If motor doesn't start and run right, first look for trouble elsewhere than in carburetor. Particularly, see that spark plugs are clean, properly adjusted, and that the porcelain core is not cracked in either plug. Try new plugs. Check the adjustment of valve tappets. Make sure that there is good compres-sion in both cylinders. See that the throttle and spark controls are properly adjusted. Also refer to "Summary of Motor Troubles and Their Causes"

Schebler De Luxe Carburetor
The Schebler carb was used on the 1930, 1931 and 1932 models. In 1933 Harley switched to Linkert carbs which look and function almost exactly the same.

1-Choke lever; OPEN position (all the way down) is normal running position of lever; 2-Air port shutter, open only for high speed; 3-Air cleaner; 4-Low speed needle lift lever; 5-Low speed adjusting needle; 6-High speed adjusting needle; 7-Lock screw; 8-Throttle stop screw, with which the closed throttle motor speed is regulated; 9-Throttle lever.

Carburetor Flooding 
Flooding may be caused by a leaky float needle valve (dirt or a poor seat), a faulty cork float, or a damaged bowl lock nut packing washer. If a solo machine equipped with "Jiffy Stand", is parked on an incline, or the stand is improperly adjusted or bent, allowing machine to lean farther than normal, the carburetor, regardless of its perfect condition might over-flow.

To Adjust Carburetor
Needle 5 (image above) on back side of carburetor adjusts the mixture for low and idling speeds. It controls carburetion up to 15 miles per hour, and affects it up to 25 miles per hour. This needle is mounted in a lever which is actuated by a cam on end of choke shaft. By means of this arrangement, when choke lever is raised for starting and warming up motor, the needle is also lifted away from its seat—enriching the gas mixture. When choke lever is moved to OPEN position, the needle is also moved back to its original position. When adjusting the low speed needle, choke lever must be at OPEN position (all the way down).

Needle 6 on forward side of carburetor, adjusts the mixture for high speed. It's adjustment affects carbureration above 15 miles per hour, and controls it entirely above 25 miles per hour. Both needles turn down (to right) to make mixture leaner at the re-spective speeds for which they adjust. Backing them out (to left) makes mixture richer. Both needles are held in whatever positions they may be turned to, by a spring and plunger which drops into .notches in the needle adjusting screw.

A carburetor once properly adjusted requires little, if any, re-adjusting. At the most, it should not be necessary to adjust the needles more than one or two notches richer or leaner to correct mixture for a change in weather conditions.

A carburetor that is badly out of adjustment may be re-adjusted as follows: 
Turn both the low and high speed needles all the way down (to right). Then, back up (to left) low speed needle about 2 turns, and high speed needle about 1.5 turns. With needles in these positions, motor will start, but mixture will probably be too rich. Start motor and after choke has been moved to OPEN position and motor is normally hot, correct the adjustment of both needles.

Adjust for low speed first. Turn needle 5 down (to right) one notch at a time until mixture becomes so lean that motor misses and is incliner' to stop; then, back needle up seven to ten notches or until motor hits regularly with throttle closed and spark advanced. Next, adjust throttle stop screw 8 as may be necessary to make motor idle at proper speed with throttle closed. Turning screw to right makes motor idle faster. Turning screw to left makes motor idle slower.

Don't idle a motor at the slowest possible speed, because an extremely slow idling adjustment causes hard starting. Before making this idling adjustment, be sure control is adjusted to fully close throttle.

After low speed adjustments have been completed, run machine on the road to make high speed adjustment. Run at various speeds between 20 miles per hour and wide open. Have spark fully advanced. Turn high speed needle 6 down (to right) a little at a time until mixture becomes so lean that motor doesn't respond to throttle, and backfires (spits) through carburetor; then, back needle up a notch at a time until motor responds to throttle, accelerates without back-firing (spitting), and hits evenly at high speeds or with wide open throttle.

Auxiliary Air Port
When driving with wide open throttle, the speed of machine can usually be increased a little by opening auxiliary air port in air cleaner connection. Moving shutter 2 (image above) upward opens port. Shutter should be kept- in closed position for all ordinary service.