| Tuning your Harley Davidson carburetor is simpler | | | | The air cleaner assembly MUST be installed prior to |
| than most think and can be performed with a few | | | | starting the engine, not only to hold the carb in place |
| common tools. This simple procedure is a great | | | | but to prevent any backfire while tuning. With |
| Harley tech tip that applies to all Harley models from | | | | everything back in place start the engine as normal |
| 1989 to 2006 that use the CV (constant velocity) | | | | and bring up to operating temperature. Do not |
| style carburetor. Earlier models equipped with the | | | | overuse the enrichener (choke) and don't let the bike |
| older butterfly style carburetors (pre-89 Evo's, | | | | idle for more than 5 minutes. |
| Shovelheads, and Ironheads) are excellent candidates | | | | With the engine warmed up and at idle you may now |
| for upgrading to a newer Harley CV carburetor. | | | | fine tune the idle mixture screw for optimal |
| Before you rejet your carburetor it is recommended | | | | performance. With the engine idling slow (no more |
| that you perform the following tuning procedure first. | | | | than 900 rpm) turn the screw inward (clockwise) |
| Once the mixture has been properly tuned as | | | | SLOWLY until the engine starts to stumble. Note: you |
| described here you may not need to rejet the | | | | are working with the screw upside down so think |
| carburetor. | | | | about the orientation. |
| Preparing the carburetor for tuning will require | | | | Raise the idle speed if necessary. Now turn the idle |
| removal from your Harley-Davidson's engine but this | | | | mixture screw outward until the engine begins to run |
| is easily accomplished. The entire removal and | | | | smoothly + 1/8 of a turn. Maintain proper idle speed |
| installation procedure can be found in your service | | | | and repeat the adjustment each time you adjust the |
| manual. With the carburetor removed, place it on a | | | | idle speed. Blip the throttle a couple of times and |
| sturdy work surface upside down. The carburetor | | | | observe the results. If the engine responds quickly |
| has a small cylindrical tower protruding from the base | | | | with a smooth blast and no backfiring through the |
| of the rear throat against the back side of the bowl. | | | | carburetor, you have your idle mixture set correctly. |
| The tower is plugged with a soft metal insert | | | | If backfiring occurs through the carburetor then |
| covering the idle mixture screw. Gaining access to | | | | adjust the idle mixture screw out another 1/8 turn. |
| this screw is key to fine tuning and must be drilled | | | | Normally, the idle mixture screw should only be |
| out. The metal plug is very soft and only requires a | | | | between 2 and 3 turns out from it's seated position. |
| household drill and a 1/8" bit. Secure the carb in either | | | | Adjusting the mixture screw out too far will result in |
| a vise or clamp and drill a hole into the plug making | | | | an overly rich, low RPM fuel mixture. Avoid tuning the |
| sure not to "punch" through too fast. You don't want | | | | idle too rich, thus leading to poor gas mileage and |
| to damaged the mixture screw just below the plug. | | | | fouled plugs. Set this just beyond the point of |
| Tip: I found to keep from drilling too far into the plug | | | | backfiring (coughing) through the carburetor. Never |
| is to wind electrical tape around your drill bit to form | | | | remove the mixture screw with the carburetor |
| a thick band about 3/16" from the tip creating a stop | | | | upright as the spring, o-ring, and washer will fall out. |
| point. | | | | Take your newly tuned bike for a ride and note how |
| With a small hole now drilled into the plug, pry the | | | | it idles and responds off idle. If you experience any |
| plug out using a pick or awl. You can also thread a | | | | coughing through the carburetor not experienced |
| sheet metal screw into the drilled hole and use this to | | | | before, adjust the mixture out another 1/8 of a turn. |
| pull the plug out. With the plug removed, clean the | | | | Black smoke seen from the exhaust at idle or a |
| area around the mixture screw so no metal | | | | feeling of sluggishness off idle indicates you may |
| fragments remain. | | | | have set the mixture too rich. If your bike is now |
| Adjustment Method: Using a small flat head | | | | idling steady and responds well from a start then you |
| screwdriver, turn the screw clockwise until it gently | | | | are all set. If your engine still runs lean (coughs or |
| seats. Do no tighten as this will damage the screw or | | | | hesitates) you should move on to rejetting your |
| seat. Now turn the screw outward 2 turns to | | | | carburetor. The same stock Harley Davidson |
| establish a starting point. | | | | carburetor has been used on all production bikes |
| Reinstall the carburetor back on your bike making | | | | since 1989 due to it's reliability and ability to adapt to |
| sure to replace the fuel hose clamp and vacuum lines. | | | | different conditions. With just the right amount of |
| It may be a matter of dexterity but I prefer to | | | | tuning the CV carburetor will support any stock to |
| install the cables before pushing the carb back onto | | | | mildly modified Harley. |
| the manifold. Test the throttle for any binding and | | | | Enjoy the ride! |
| double check all connections. | | | | |