Carb Maintenance & Synchronization

Experiencing rough idle, galloping, backfire, and uneven acceleration? This is a good indication you need the carbs synchronized. The procedure is fairly similar for all multi carb engines including Goldwings, V-max and a great many more. The idea is to get all the individual cylinder vacuums to match. I'll use the standard inline four as a demo type. First thing pull the seat & fuel tank so you can get at the carb adjustments and vacuum connections. You'll need an auxiliary fuel supply as the tuning will take enough time to drain the carbs dry. Here's a neat little tank that will do the job with minor cash outlay.

Fill the auxiliary tank about 1/2 full. Slip the hose over the spout tip. There’s no need to vent the tank as the sides are soft and will "inhale" as fuel is used. Hook up the tank to one of the fuel lines (some bikes have (2) lines that feed all the carbs, one is standard the other is reserve. Using a 1/4" drill bit or short Phillips screwdriver, plug the remaining lines so fuel doesn't spray all over. Lay the tank on the frame or faring just so gravity can do its thing. Start with the idle fuel mixture settings. Check the service manual for how many turns out the mixture screws are supposed to be set. (Some mixture screws are non-adjustable. Skip this step and go to synchronization). Start engine & allow it to warm up. Place a fan or furnace blower in front of the engine to keep from overheating. (Mixture screw tips are precision machined points and may be easily damaged if tightened into seats). One screw at a time, turn mixture screws in until they seat, counting number of “turns in” as you go. Record this number for later reference if needed. Once seated, back them out to factory recommendations. Turn the screw on #1 carb out until you notice a roughening idle. Go back to the original setting and turn in until the idle roughens again. Set the screw at the mid point of these two settings. Repeat with other mixture screws. Some carbs use a fuel mixture screw and some use an air bleed screw. The procedure is the same for both. On the fuel mixture screw type, turning screws clockwise is leaner; counter clockwise is richer. The air bleed type is just the opposite.

Carburetor Synchronization:

To sync the carbs you will need a gauge set or one of the more popular carb stick synchronizers. These can be purchased through "Dennis Kirk" 1-800-328-9280 or www.JCWhitney.com, (Keyword: Carburetor Synchronizers). Most tuners prefer the mercury carb sticks as they are more reliable in the long term and don't require any needle flutter calibration. Hose adapters are required for some motorcycles. They are not included with the tool and are a separate purchase. They are listed with the sync tools. I recommend the purchase of a sync adjuster screw tool. This tool works the locknuts and adjuster screws.

Support the sync tool on a lever or handle bar grip and connected to the respective carbs. Keep the hoses clear of engine’s hot surfaces. For tuning Yamahas, go to the "YICS" section for the tuning procedure.

With fan on in a well ventilated room or area, aux fuel connected, idle mixture set, and carburetor synchronizer tool connected, and engine warmed to normal operating temperatures, set the idle speed to about 1000 RPM and watch the sync gauges. Pick a carb and set the vacuum of the others to match this one. Pick one that is not the highest or lowest, but in the middle of the readings. Some carburetors have one non-adjustable carb that the others are adjusted to. Check the service manual or call your local dealer if you are not sure if your carbs are this type.

The majority carbs have adjusting screws between the carbs. (On older Kawasaki KZ type carbs, adjusting screws are located under the carburetor top cover caps.) Adjusting screws have locknuts to maintain adjustments. You may notice your adjustments change slightly when tightening locknuts. Compensate for this accordingly as you work. The adjuster found between carbs 1 & 2 balances those two carbs. The adjuster found between carbs 3 & 4 balances those two carbs. The adjuster found between carbs 2 & 3 (or center) balances the left and right carb sets (1-2 & 3-4) to each other. On older Goldwings, screws are between carbs as above, but center adjuster is on the left side. The order in which the carbs are adjusted doesn't matter as long as they all come out balanced in the end. When adjusted as level as possible, you’re finished.

Sync adjuster screws may have a drop of red or yellow paint to mark or seal the factory sync settings. While synchronizing, open and close the throttle slowly to avoid drawing mercury into the engine.