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syncing the carbs

what you'll need:
Time needed: If you decide to add the tubing in order to make future carb syncing easier, plan on at least one full day. I chopped it up into two days in order to not go batty. After that, syncing the carbs themselves should take no more than an hour, depending on how out-of-sync the carbs are (most of that time is spent removing the airbox and stuff, so just checking the carbs without adjusting them will take like 5 minutes).
  • about a yard of plastic tubing, 9mm in diameter
  • Two 1/4" barbed valves (we used some home sprinkler system plastic valves) Picture here.
  • One 1/4" tee connector (again, we used one from a home sprinkler system) Picture here.
  • 10mm socket
  • 4mm hex (allen) wrench
  • 6mm hex (allen) wrench
  • Philips screwdriver (normal)
  • Philips screwdriver (right-angle, sometimes called offset)
  • needlenose pliers
  • funnel and clean container for antifreeze (if you decide to completely remove the radiator)
  • carb sync tool

Note: I've heard murmurings on the SV mailing lists that not all SVs have the stock T-connector. I'm not sure yet whether it's a year-model thing (i.e my 2001 SVS has it, but a '99 SV might not), or a California vs. 49-state model thing. Once I get some pictures/text from those who have the non-T-connector model, I'll be sure to post them, too. Sorry about any potential confusion in the meantime.

Note: Thanks to Discerning Reader Erik, who points out that you'll want to make sure that the inner diameter of the tubing is the same size as or slightly smaller than the valves. Home Depot (and, quite possibly, everyone else) apparently marks the size of the tubing as the outer diameter of the tubing.

Another note on the tubing, from Discerning Reader Warren: "Also you will need to make each line coming from the carb the exact same length in order to ensure proper syncing. If one line is a lot longer it will be much harder for that carb to pull suction on the sync tool and will cause a misreading. (the tool could say your carbs were off even if they were dead on because the carb with the longer line was under more stress and couldn't pull as hard)"

If you do the tubing, in the future when you want to test the carbs, you'll just need the carb sync tool. If, then, the carbs need adjusting, you'll need the socket wrench, allen wrenches, and offset screwdriver to get to the carbs and their adjust screw, but that's all.

There are a great many things to love about the SV650S. It's a wonderful bike. In the name of cosmic balance, however, Suzuki felt it necessary to make a few things about SVS maintenance more irritating than being nibbled to death by ducks. Syncing the carburetors is one of these things.Granted, carb syncing is only recommended every 7000 miles (according to the factory Suzuki manual), but trust me, after trying to get at that front carb nipple just once, you're going to have cold sweats at the thought of ever putting yourself through that again. So, in my humble opinion, it's best to put yourself through this once, put the tubing and valves on, and make future carb-syncing a breeze.

Carb syncing measures the amount that the throttle valves in each carburetor are open at any given time. If the valves don't open simultaneously, the bike will run a little roughly (a good indication that you might want to sync the carbs). The procedure below uses a dial-type vacuum gauge; there are also mercury stick gauges and gauges with steel rods (as opposed to mercury). It's more or less personal preference which type you use. No matter which type of gauge you use, it will probably have four long rubber hoses: one for each carburetor on a four-cylinder bike. If you've got a SVS, you've got a two-cylinder bike, so you'll only use any two of the hoses, and ignore the other two. The hoses on the gauge connect to vacuum ports on the carburetors; in my modification below, we're going to be hooking up plastic tubing to the vacuum ports and routing the tubing to an easily-accessible place on the bike, then plugging the tubing up with valves. When we go to actually sync the carbs, we'll attach the gauge hoses to the valves on the tubing instead of to the carburetors directly.

As you've probably figured out, the pre-procedure is what makes syncing the carbs a pain in the ass. I figure I might as well be honest about that. No false advertising here, boy howdy.

The first thing you're going to want to do is remove both seats. The rear just pops up when you unlock it with the key. To remove the front seat, use a 4mm hex wrench to unbolt the black plastic frame covers on both sides, and remove them. Next, use a 6mm hex wrench to unbolt the seat, and it'll come right off.

Next, prop up the fuel tank. Underneath the seats, there should be a long piece of metal (it's attached with a little clip underneath the seats). Take that out and hang onto it for a moment. Center the handlebars and use a 4mm hex wrench to unbolt the two tank mounting bolts that are up by the triple clamp. Once those are removed, you can tilt the tank backwards on its hinges. Use the aforementioned long piece of metal to prop up the tank (put one end into the hole on the triple clamp steering stem bolt, and the other end into one of the mounting holes on the tank).

svs_tankup svs_tankup2

Now we're going to remove the airbox. Stand at the right side of the bike and look at the bottom of the airbox; you should see a black rubber tube going up into the airbox on the lefthand side. Squeeze together the metal clamp holding it on (a needlenose pliers can help here), and disconnect the hose from the airbox. Move around to the left side of the bike. On the righthand side of the airbox, you'll find two similar hoses with clamps going up into the airbox. Disconnect these in the same way (hint: the one on the left is a bit tricky; you'll probably need the needlenose pliers).


After the tubes are disconnected, you can remove the airbox. Grab it firmly at the top, and pull straight up. Wiggle a bit if necessary, but it should pull right off, exposing the carburetors. At this point, you'll need to be extra careful not to let anything fall into the carburetors. If you're going to leave the bike for a while, unprop the tank and just set it down. Even falling leaves can drop right into the carburetors and make your life suck.


If you're really masochistic, you can go ahead and start futzing with the carbs now. I started trying to do that, and ended up with bruises and scrapes all over my hands from trying to squeeze them in little crevices. I found it was much easier to move the radiator out of the way, so that's what I'll tell you to do.

The fairing is connecting to the radiator via one of those little grommets, so you'll need to move part of the fairing out of the way. Using a 4mm hex wrench, remove the three rearward hex screws on the fairing on each side of the bike. That'll give the fairing enough flexibility to allow you to pull it off of the radiator -- though be careful not to yank too hard on the pretty plastic, OK?

Next, remove the horn bracket that attaches the horn above the radiator. It takes a 10mm socket, and you can just leave the horn hanging from the wiring; you just need to unbolt it to get it out of the way.

Now, unhook the temperature sensor wiring that leads to the radiator. If you stand on the righthand side of the bike and look just inside the frame, there's a black ziptie holding some wiring in place. It's got a little locking mechanism; the ziptie will loosen if you pull up on the little plastic lever right where it tightens (this hopefully makes sense when you're looking at it). No need to remove the tie, just loosen it. Right next to the ziptie, there'll be a big rubber sleeve holding two connectors and one pair of wires that isn't connected to anything; you'll want to disconnect both of the connectors and slide them out from under the ziptie.


Go back to the radiator now. On the righthand side of the bike, there will be one lower mounting bolt. Remove itwith a 10mm socket. Ditto for the upper mounting bolt on this side. You might need to remove the radiator cap in order to remove (and later, replace) the upper bolt. On the lefthand side of the bike, there's only one upper mounting bolt (no lower one). Remove it, too. Now you can move the radiator out of the way. Just pull it down (gently!) until you start to feel resistance from the radiator hoses. Get underneath the bike on the righthand side, and look up at the carburetors. Behind where the radiator fan was, at the bottom of the front carburetor, you should see a black rubber cap. This is the holy grail. You need to remove this cap. If you feel like you can get your hand (or some pliers) in that space easily enough to remove the cap, you're done with the radiator. If not, you'll need to drain the radiator fluid, remove the main hoses and smaller reserve hose (up at the top of the radiator), and remove the radiator completely. All I'll say about that is that the drain bolt is on the righthand side, just above and to the right of the crankcase. Get a funnel. When you loosen that bolt, antifreeze will shoot straight out at you. Don't say I didn't warn you.

OK, now you've got everything out of the way, and we can actually start in on the carburetors now. Yay!

procedure - inserting new tubing.
We'll do the rear carburetor first, because, although it's a little more complicated, it's far easier to get to all of the parts. First of all, take a look at the carb and the hoses so that you can get an idea of what's going on. The rear carb's vacuum intake nipple is in use already, which is why we needed a new tee connector. There will be a hose running from the underside of the gas tank into an existing tee connector; from that connector, there's a hose going to the rear carb nipple, and a hose going to the fuel pump (a square box alongside the frame on the righthand side of the bike). Here's a bad diagram of this. We just want to insert another hose into this mess, that can be re-routed to the outside of the bike (for better accessibility) and plugged with a valve. We don't want to cut the existing tubing, since we don't trust ourselves with scissors, so we'll just add another tee connector and small section of tubing. And here's a bad diagram of what it'll look like afterwards.

First, cut off a section of the clear plastic tubing. It doesn't matter how long, but one to two inches will work well. Fit one end (doesn't matter which) of your new tee connector into one end of the tubing. If it doesn't fit, take a Philips screwdriver, and insert it into the tubing to stretch it. Pull out the screwdriver and insert the tee connector; the tubing will shrink to fit. Now, find the hose that runs from the fuel pump (not the gas tank) to the existing tee connector, and disconnect it at the connector. Insert your short length of new tubing onto the existing connector, and insert the existing tube onto your new tee connector. Again, if any of the tubing is too small, stretch it out with a Philips screwdriver. If any of the tubing is too large in diameter to fit snugly, a small ziptie will work to keep it on the connector.

Next, take the remaining length of new tubing and attach one end onto the remaining side of your new connector (again, streching it with a Philips screwdriver first if necessary). Route the new tubing over to the righthand side of the bike; the frame makes a triangle right under the gas tank, and this is where I put mine. Measure out enough tubing so that you can get to it easily, and cut off the rest. Stretch out the end with your Philips screwdriver, and insert one of the 1/4" valves. For normal operation, make sure the valve is set to "closed." That's it! You're done with the rear carb!

new_rear_piping new_rear_piping_lbl

Now it's time for the front carburetor. Remember way back in the pre-procedure, when you located that little rubber black cap on the lower righthand side of the front carb? Guess what? Now you get to remove it. You may do this by whatever means necessary -- we're not saving the cap, so feel free to have at it with pliers, screwdrivers, whatever. Every time you swear while doing this, just think of how much more fun it wouldn't be if you hadn't moved the radiator first. I'm just sayin'.

I'll assume you've got that rubber cap off. Congratulations; that's the hardest part of this entire procedure. The rest is easy. Using your trusty Philips screwdriver, stretch out one end of your remaining piping. Then, slide it on the metal nipple (you know, the thing under the rubber cap that you just hurt yourself removing). You want to slide it on as far as possible, so if it doesn't go on that far, take it off and stretch the tubing out more with the screwdriver. Once that's on, you just need to figure out how to route the tubing so that it stays clear of the throttle cables (those shiny thin metal cables just above the nipple). I routed the tubing underneath and then over to the righthand side of the frame, through the ziptie that you loosened in the pre-procedure (the one that holds the temperature sensor wires that you disconnected), and out underneath the frame right next to our other valve. If there's extra tubing, cut it off, stretch out the end with the screwdriver, and pop on your other valve. Make sure this valve is set to "closed," too. That's it! Easy, once that cap is off.

The first picture below is from the outside of the bike, looking through the righthand air hole in the fairing. I'm pointing at the front carb nipple with a flathead screwdriver. The second picture is from the top, looking down at the carbs. Those metal cables in there are the throttle cables.

nipple_from_outside_lbl front_carb_nipple

attaching_tubing attaching_tubing_lbl front_carb_tubing front_carb_tubing_lbl

bike_with_valves new_valves

procedure - testing and syncing the carbs
OK, you just wasted half of your life away, and you haven't even started the actual carb syncing yet. Fear not, this is a piece of cake now with your new valves. Simply take your carb sync tool and attach one hose onto each of your new valves. Most carb sync tools have four hoses (for a four-cylinder bike); it doesn't matter at all which two you use. Now, here's the fun part. Turn the valves to "open," and start the bike. It'll be loud and sound weird without the airbox on. One piece of advice: don't put your head near the carbs for too terribly long. Remember those hoses that you disconnected to remove the airbox? With the bike running, you'll be huffing lots of fumes coming out of those tubes, which would normally be going up into the airbox. Yum.

Now, take a look at your carb sync tool. Every tool works differently, but with my dial gauge, I've got two rapidly fluttering needles. A dampening screw on the tool will slow down the fluttering; you don't want to stop the needles, but slowing them so that they're readable is a plus. No matter what tool you have, you want the needles/mercury/whatever to be in the same place for each carb. If the needles aren't in the same place on the two dials, or the mercury is floating in different levels, you need to sync up the carbs. You can see in the second picture that my carbs were slightly out of sync -- the first dial reads a bit below 200, while the second dial reads just above 200 (Note: on these dial gauges, you only really pay attention to the location of the needles. All the colors and writing and junk is for car tuneups -- we don't care about any of it, really.).

carb_sync_attached_lbl carbs_out_of_sync

If you've got to adjust your carbs, it's pretty easy. Stand on the lefthand side of the bike, and look down at the carbs. Remember not to breathe too deeply if your bike's still running. You'll see a screw close to the top of the rear carburetor. That's the adjust screw. There's only one for the SVS, since it has two carburetors (Peter's VFR, which has four carbs, has three adjust screws). All you need to do is stick your offset Philips screwdriver in that screw and turn it. Experiment turning it one way or the other -- you won't hurt anything -- and watch the dials. You'll figure out which carb you're tuning by which gauge moves, and just keep moving the screw until it lines up with the reading on the other dial. That's it. Don't breathe too deeply over there; those fumes are nasty. Turn off your bike, remove the carb sync tool, and don't forget to move the valves to their closed positions.

carb_adjust_screw carb_adjust_screw_lbl

That's it! Now you just need to reassemble everything: airbox on, radiator back on, horn re-attached, fairings screwed tight, tank down, seats back on, frame covers back in place, and you're ready to ride again!

If you do the extra tubing, in the future, you won't need to do anything but hook up the carb sync tool to the valves, open the valves, and run the bike in order to check the carbs. If they need syncing, you'll need to remove the seats, prop up the tank, and remove the airbox to get to the adjust screw, but you don't need to mess with anything else. See how much easier that is?