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Carburetor Tuning on Harley Davidson

Carburetor Tuning on Harley Davidson

Tuning your Harley Davidson carburetor is simpler than most feel and can be carried out with a handful of common tools. This easy method is a excellent Harley tech tip that applies to all Harley designs from 1989 to 2006 that use the CV (frequent velocity) fashion carburetor. Previously models equipped with the older butterfly style carburetors (pre-89 Evo's, Shovelheads, and Ironheads) are excellent candidates for upgrading to a more recent Harley CV carburetor. 

Before you rejet your carburetor it is suggested that you perform the subsequent tuning method first. When the mixture has been correctly tuned as described here you might not need to rejet the carburetor. 

Preparing the carburetor for tuning will need elimination from your Harley-Davidson's engine but this is quickly achieved.

The complete removal and set up procedure can be observed in your service manual. With the carburetor removed, place it on a sturdy perform floor upside down. The carburetor has a little cylindrical tower protruding from the base of the rear throat in opposition to the back again side of the bowl. The tower is plugged with a comfortable metal insert covering the idle combination screw. Gaining access to this screw is key to fantastic tuning and need to be drilled out. The metal plug is very gentle and only requires a family drill and a 1/8" bit. Safe the carb in both a vise or clamp and drill a hole into the plug making certain not to "punch" by way of as well quickly. You do not want to damaged the combination screw just beneath the plug.

Tip: I discovered to maintain from drilling also far into the plug is to wind electrical tape close to your drill bit to sort a thick band about 3/16" from the tip generating a stop point.

With a tiny hole now drilled into the plug, pry the plug out utilizing a select or awl. You can also thread a sheet metal screw into the drilled hole and use this to pull the plug out. With the plug eliminated, clear the locationall around the combination screw so no metal fragments stay.

Adjustment Technique: Using a small flat head screwdriver, turn the screw clockwise till it gently seats. Do no tighten as this will injury the screw or seat. Now turn the screw outward 2 turns to establish a starting stage.

Reinstall the carburetor back on your bike creating sure to substitute the fuel hose clamp and vacuum lines. It may be a make any difference of dexterity but I want to install the cables prior to pushing the carb back again onto the manifold. Test the throttle for any binding and double verify all connections.

The air cleaner assembly Ought to be installed prior to commencing the engine, not only to maintain the carb in area but to stop any backfire while tuning. With every thing again in place begin the engine as normal and deliver up to operating temperature. Do not overuse the enrichener (choke) and don't let the bike idle for a lot more than five minutes.

With the engine warmed up and at idle you might now fine tune the idle mixture screw for optimum performance. With the engine idling slow (no far more than 900 rpm) turn the screw inward (clockwise) Slowly until finally the engine starts to stumble. Observe: you are functioning with the screw upside down so assume about the orientation.

Elevate the idle pace if needed. Now turn the idle combination screw outward until the engine commences to run smoothly + one/eight of a turn. Preserve correct idle speed and repeat the adjustment every single time you modify the idle velocity. Blip the throttle a few of instances and observe the results. If the engine responds swiftly with a smooth blast and no backfiring through the carburetor, you have your idle combination set properly. If backfiring occurs by way of the carburetor then adjust the idle combination screw out another one/8 turn. Normally, the idle mixture screw ought to only be involving two and 3 turns out from it's seated placement.

Adjusting the mixture screw out as well far will result in an overly prosperous, lower RPM fuel combination. Stay away from tuning the idle also abundant, thus top to poor gasoline mileage and fouled plugs. Set this just past the stage of backfiring (coughing) via the carburetor. By no means take away the combination screw with the carburetor upright as the spring, o-ring, and washer will fall out.

Take your freshly tuned bike for a ride and be aware how it idles and responds off idle. If you knowledge any coughing through the carburetor not seasoned just before, regulate the mixture out another 1/eight of a turn. Black smoke witnessed from the exhaust at idle or a feeling of sluggishness off idle indicates you may possibly have set the combination too rich. If your bike is now idling continual and responds well from a start then you are all set. If your engine nevertheless runs lean (coughs or hesitates) you must transfer on to rejetting your carburetor. The very same stock Harley Davidson carburetor has been utilised on all creation bikes since 1989 due to it's reliability and potential to adapt to different conditions. With just the proper volume of tuning the CV carburetor will assist any stock to mildly modified Harley.

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1/4/2015 3:33 AM
I could read a book about this without finding such real-world aproapches!