How To Synchronize Your Carbs - It's All About Balance

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You've read your manual, you've got the tools set up and you're ready to go, so let's get started. First make sure you've got plenty of ventilation. For most of this exercise the engine will be running, and while the smell of burning gasoline may be heady, the byproducts of combustion can put you to sleep for a very long time if you're not careful. I suppose I should also pass on the obligatory warning about spilling gasoline all over the place, especially when you're working with a hot engine, so consider it passed.

The first step is to remove anything that impedes access to the carburetors. Your manual will provide the details, but in most cases it's going to mean that at least the seat, the fuel tank and perhaps some of the bodywork will be coming off. Stow it all in a safe place before proceeding.

If required, connect your auxiliary fuel tank and hang it in a secure location high enough to ensure good fuel flow to the carburetors. If you plan to dangle the thing from the handlebars, make sure there's no chance it'll contact the exhaust pipes.

Sometimes things can get a little tricky here, particularly if you're working on something with EFI or a tank-mounted fuel pump. If that's the case you may be forced to keep the tank and its attendant fuel lines and wiring harness connected to the bike while you fettle the adjusting screws. In some instances the tank will be hinged to accommodate you; in others you'll just have to jury-rig something. As always, consult your manual; the answer is lurking in there somewhere.

The manual should also identify the correct vacuum ports, which will have either rubber caps or threaded plugs to seal them, and the "master" or reference carburetor you'll synchronize the others to. If the vacuum ports are threaded, you'll need adapter tubes to plug in your gauge (normally these are supplied with the gauges, but not always), so make sure you know what you'll need beforehand.

Following the manual or gauge manufacturer's instructions, connect the gauges in order-gauge number one to cylinder number one and so forth-and if need be, calibrate them according to the manufacturer's instructions. Then position them where they'll be easy to see yet out of the way, making sure none of the hoses foul any of the carb linkages.

Double-check your hoses and make certain there's nothing left open or unaccounted for, then start the engine (don't forget your fan) and let it come up to operating temperature before setting the idle to the manufacturer's recommendations. If the carbs are way out of whack, the bike may not idle well. If that's your situation, just get it as close as you can for the time being and proceed.

With the engine idling, observe your gauge. In most cases the carburetors should be set to identical marks, but occasionally you'll find some that are set unequally, so double-check the gauge readings against the manual before you start spinning adjustment screws.

If you're working on a twin, the procedure is dead simple. Normally there will be only one adjusting screw, and which way you'll turn it depends on the readings you're getting, but my bet is you'll be turning it clockwise to start.

As a rule carburetors are fairly sensitive to adjustments, so go slowly and work in small increments; 1/8 turn at a time should be about right until the gauge readings are identical (or at the factory-recommended settings).

When you're satisfied with the readings, gently raise the engine speed to a fast idle and then allow it to drop to the base setting to settle the slides. Recheck your work, performing any fine adjustments as required.

A word to the wise: You don't have to go crazy here-a fast idle is all that's required. If you're using a mercury gauge and you rev the snot out of the engine, the high vacuum created when the slides drop down can suck the mercury clean out of the gauge and straight into the cylinders. If that does happen it's not necessarily a disaster, but it will put paid to your synchronizing efforts until you can refill the gauge, and you'll have to change the oil and filter to get rid of the ingested mercury.

Triples and fours are a little more complicated, though not by much. Essentially the procedure is the same as that of the twins; there are just more cylinders (and adjusting screws) to deal with.

When you're happy with the adjustments, rev the engine to a moderately fast rpm-somewhere around 2500 to 3000 works nicely-and make sure the gauges remain equal. If they don't, but they remain aligned at idle, look for a vacuum leak, worn or sticking slide, or some sort of mechanical problem in the linkage.

The final step is to recheck your idle speed before disconnecting the gauges and putting the bike back together. Make sure all the vacuum caps and lines go back in the right place, and don't forget any clips, especially those that secure the fuel lines. In fact it's always prudent to start the engine one last time after the fuel and vacuum lines are reconnected but before any major body pieces are reinstalled, just to make sure everything is as it should be.

Tech Tip
The Lost Key Chronicles
A couple of months ago I was with a group of about 300 people taking part in a dual-sport ride. We were preparing to leave when the rider next to me reached for his ignition switch, said "Uh-oh," and began searching his pockets. Within 30 seconds he realized his keys were lost, and the next thing you know there were 300 people combing the parking lot looking for a tiny DR650 key. Believe it or not we found it-but if we hadn't he would have been truly screwed. The guy was miles from home with no spare. Yeah, he might have hot-wired the bike and made the ride, but that would have been a hassle, and most likely his day would have ended right then and there. The only bright side was that (a) he'd trailered to the event so at least he could get the bike back home, and (b) he lost the keys in a gin-mill parking lot, and the joint, which had excellent ambience (if you catch my drift), was open.

You might not be so lucky, so here are a few places to stash a spare key.

* Tossing a spare in the saddlebag, tool kit or maybe a stash pouch is always popular, but make sure the spare is accessible without unlocking anything!

* I've seen quite a few guys wire or tie-wrap a spare to some out-of-the-way place on the frame. Make sure the hiding spot is well protected and out of sight, and don't forget where you hid it.

* Inside the headlight is a great spot-warm, dry and protected, and you can usually pop the headlight off without too much trouble.

* Inside the taillight-ditto. When I was a dealer we always stashed a spare key in the taillight just in case. You'll need a screwdriver to remove the lens, but they're usually easy enough to come by, and in a worst-case scenario a rock makes a passable substitute.

* Inside the handlebar may work but it can be tricky. In the first place, modern handlebars aren't always hollow, and in the second, you'll normally need tools to remove the throttle or a razor blade to remove the left-side grip and retrieve your hidden key. But either method is preferable to the alternative. If you do hide the key in the bars make sure it can't slip all the way to the center. Foam wrapped around the key will usually do the trick.

* A hide-a-key box can be bolted, tie-wrapped or even duct-taped to the inside of the fender or frame or even to a convenient engine bolt. Tape the box shut and you should be all set.

Obviously you don't have to stash a spare on the bike; you can hide one in your favorite riding jacket or carry a flat-style spare in your wallet or anywhere else. The idea is to have a spare available in an emergency, and by extension it needs to be stored in a safe, secure, inconspicuous spot where it's protected from the elements and the unsavory types who might really like to ride your bike like they stole it.