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Carburetor Synchronization

Since I took the time the other day to synchronize the carbs on my Rotax 582, I thought I would write a little about it. The following is my opinion only, after being a motorcycle mechanic for many years. 

So you've managed to assemble your new powered parachute, installed your beautiful new Rotax dual carb engine, and rigged your chute. Now you're ready to fly. Well not quite. Some will be satisfied to adjust the idle, do the run-in procedure, and call it done. But those who strive for perfection will take the time to properly adjust the mixture and sync the carbs. Today I'll talk about carburetor synchronization. 

Whenever you have a muticylinder engine, where each cylinder if fed by its own carburetor, its a good idea to sync the carbs. If you don't do this, it is possible that one of the cylinders will be doing more work than the other at idle and mid range throttle openings. While this will not usually cause any harm to the engine, it can cost you in engine smoothness and mid range performance. 

The idea behind synchronization is to make the throttle slide opening exactly the same on both carburetors throughout its range of movement. You will need a mercury carb sync tool to do the job. These tools are available from motorcycle dealers, auto parts stores, and other places. Do not be tempted to by the dial type vacuum gauges, only the mercury type are worth owning. 

Bing has made carb synchronization an easy job by installing vacuum ports (primer ports), and by putting the adjustable components in easy to reach locations. On the left side of the carbs, near where they fit into the rubber mounts, you'll find a small male hose fitting, covered by a rubber stopper. Remove the stopper and attach the hoses from your tool (most sync tools have 4 hoses, we'll use only two, one for each carb). Hang the tool away from the prop and start the engine. With engine at idle, take a look at the level of the mercury drawn up into the transparent tubes. Most likely one will be lower than the other. Find the carb that is drawing the mercury up higher, and turn the throttle stop adjusting screw clockwise until the levels are even. Go ahead and adjust the idle speed to your liking, but make sure when you are done, the mercury levels are even. 

Now on to the mid range adjustment. Shut off the engine and pull the rubber covers up off the cable adjusters on top of the carburetors so you can get to the adjustment nuts. Start the engine and set the throttle to about 3000 rpm. Take a look at the mercury level, and after loosening the lock nut, back out the adjuster on the carburetor that has the higher level until the levels are even. Tighten the lock nut. Turn off engine. Slide covers back down. Remove tool hoses Reinstall vacuum port stoppers. 

That's all there is to it. The carbs are synchronized.