FOR THE DO-IT-YOURSELF DUCATI OWNER

SYNCHRONIZING THE CARBS

$20+ (Gauge)

Long Phillips Screwdriver, ?mm Hex for the Oil Cooler, Dial Type Vacuum Gauge or Synch Sticks if You Must Do it That Way.

Carburetor Synchronization:  the very words scare many do-it-yourselfers away.  But, there is nothing to be afraid of.  It is a very easy process and the method I use is also very cheap.  You've seen the mercury type gauges sell for upwards of $100.  Those are nice, but also unnecessary.  I use a single, $20, dial-type vacuum gauge to synch my carbs.  If you are skeptical about the accuracy, let me assure you that a mercury gauge would produce the same results.  If you still don't want to take my word for it, at the end

of the process you can perform the tried-and-true "RPM drop" method.  I'll tell how later.  First, let me explain why the carbs need to be synched.  Your bike has two carbs (if you're riding a Duc anyway).  Each one feeds a separate cylinder.  If both of the carburetors aren't feeding their respective cylinders an equal amount of mixture, then the cylinders are producing different amounts of power and that can wreak havoc on an engine.  Synching the carbs ensures that each cylinder is receiving the same mixture as the other, and thus both cylinders are doing their share of the work.  An out of synch carb can produce engine knocking, poor idle, fluctuating idle, reduced power, backfiring, etc.  So, let's get those carbs synched!

NOTE:  This procedure can also be applied to throttle body equppied bikes, assuming that the runners have a provision for the smog tubes just as carbed bikes do (which I'm pretty sure they do).  Simply hook up the gauge in the same spots as I show and use the appropriate synching screw (I don't know where it is on injected bikes, but I know there is one, sorry).

This procedure must be done while the bike is at full operating temp AND running, making everything twice as hard.   You need to work fast through everything, but some of the stuff you can do before you go and warm it up.  Also be sure that before you start your mixture screws are set exactly equal.  Screw one of the all the way in being SURE to note EXACTLY how many turns it went in, then set it back.  The other one should turn in the same amount, then set it back.  If they aren't equal, it will screw up you vacuum readings from cylinder to cylinder.

The first step is to re-install the smog hose nipples if you've already removed the emissions equipment (you didn't throw those out, did you?).  If the smog hoses are still running into the intake runners, simply pull them off to expose the nipples.  Be sure you don't pull off the hoses that go into the other side (the inside) of the runners, those are vacuum lines for the fuel pump and tank shutoff.  The emissions hoses run to the outside of the runners.

This is the nipple I'm talking about.  It's brass and has a hole running through it.

Once the hoses are removed or the nipples are re-installed, cap them off with vacuum caps.  Once you get back from warming the bike up, you only have to remove them and pop the gauge on.

Before I put on the vacuum caps, I put some grease on the nipples to make it easier to slide the cap and gauge hose on and off.  Worked like a charm.

Once back from the ride, pop off one of the vacuum caps and QUICKLY slide the gauge hose on.  You need to leave the vacuum cap on the other side or the idle will shoot sky high and you will also lose your vacuum, and therefore your fuel supply (it's vacuum operated).

Once the gauge is on, quickly wrap the fender with a rag.  You have to do this because the oil cooler will be laying right next to it and could damage the paint.

You have to remove the oil cooler and lay it out of the way in order to get your screwdriver up in there to adjust the synch screw.  Of course, you need to do all of this quickly so the bike doesn't overheat while sitting there idling.

If you've looked at the gauge by now, you're probably thinking, "What the hell has Monster Man gotten me into?  This gauge deal sucks!  Why is it bouncing all over!?!?"  Good question.  The pulses in the runners are quite rapid and all over the place.  You may have noticed that in the emissions tubes there were severe neckdowns (plastic pieces), limitng the size of the tube to about 1/16 of an inch.

They were there to smooth out the vacuum leading to the cannister.  How?  I can't say, because I'm not an engineer, I just know what they were for.  The same principle can be applied to the gauge.  If you simply pinch the hose down, you will see that the vacuum stabilizes and it reads a constant vacuum.

So, now that we have that figured out, take the gauge to one side of the bike and note the reading.  Then, very quickly, remove the gauge hose from the nipple and re-install the vacuum cap.  Then, on the other side, take off the vacuum cap and quickly install the gauge hose.

Now take the reading on that side.  If they are different, then the carbs need to be synched.  That's the fun part.

Ta-Da!  Here's a new, easy to see diagram of what screw is used for synchronization.  The synch screw is the furthest back one, and often gets mixed up with the idle screw.  Click for a larger version.

Once you've located it, turn it a bit with the screwdriver and watch the vacuum gauge.  Take a quick note of the reading, then switch back to the other side.  If they are still not equal, turn it some more, take a note, switch back to the other side, take a note, etc.  Hey, I never said it was easy!

Once you've finally got the readings equal, you're set.  Equal readings mean that the vacuum from each cylinder is identical, which means they are producing the same power, which means that at a certain throttle (idle, for example), they are flowing the same amount of air/fuel mixture.  Mercury stick synchronizers will tell you the same thing, but the gauge is way cheaper and you can whack the throttle open without fear of sucking the mercury into the engine.

And if you want to double check your findings or try to discredit my method and its accuracy, watch your tachometer, and with the engine running, remove one of the cylinders' plug wires.  The tach will immediately drop a certain RPM, usually around 300.  Then, plug the wire back on and remove the other one.  The tach should drop the same amount of RPM as the other.  That indicates they are doing the same amount of work.  I performed this RPM drop test and they came out equal.  I should note, however, that many specialists don't approve of this test because it is hard on the engine.  Even though my Ducati factory manual tells how to do it, I only did it once to double check my work.  I agree with the experts, it does seem hard on the engine and electrical system.  Some people have warned of fried electricals, so perform this test at your own risk.

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