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Syncronize Your Carbs

The Kawasaki manual has a very short section on synchronizing your carbs on page 2-8. When I say short, I mean short. Ditto for Chalkdust on page 15. For those amateur wrenches like me, this seemed to leave a lot to chance. So, while I had the tank off after adjusting my valves, I took some time to look around the carbs and as far as synchronizing them, the worrying seems to be a lot worse than the doing.

I bought a Morgan Carbtune II a while ago and haven't had the opportunity ( I think my mother used to call it procrastination) to use it until now. The Carbtune is highly rated and since it didn't cost much more than the alternatives, that's what I bought.

The Carbtune comes with a couple different sized brass adapters but they aren't needed on the Concours; the rubber hoses supplied just slide right over the vacuum ports on the carbs.

Getting The Bike Ready
  • The engine should be thoroughly warmed up before you start. Best thing to do is take it for a good long ride.
  • You're going to have to remove the gas tank for this job, so you might as well start there.
  • Assuming that you're not yet a wunderkind with your gauges and can't get the job done with the gas that remains in the float bowls, you'll have to find a way to connect the gas tank to the fuel line. I found a little plastic adapter at the local auto supply house but I've seen similar items made of  brass at Home Depot. So, get some gas line tubing and one of these adapters. The whole works should set you back all of about three bucks. ( See below for another bright idea.)
  • Set your gas tank on a bench nearby, connect the fuel lines and turn the petcock to prime. The vacuum line that opens the petcock is connected to the vacuum port on carb #2 so forget was you were just about to ask about getting vacuum to the petcock. ( I had another suggestion but the more genteel reader may consider it a bit rude.)
Hooking It All Up
  • 3 of the 4 vacuum ports are in use and have hoses connected before you start. Carbs 1 and 4 connect to the breather in the valve cover. Carb 2 provides vacuum to the petcock. Only carb 3's vacuum port is not used. It has a little black rubber condom blocking it. If you live in California, all bets are off.
  • It gets mighty warm in there so be careful not to burn yourself. I hooked mine up after just warming it up in the garage. But I have been told that this won't warm the engine up enough. Take your pick; you've been warned.
  • So pull off the hoses and plug used in normal running mode.
  • Hang the Carbtune from the left handgrip and attach its hoses to the carbs.
  • The simplest, most obvious advice is usually the best so here goes. Sort the hoses for the gauges left to right so that they run to the carbs in the same order, left to right. Told you it was simple, didn't I.
Synchronize Your Carbs
  • The actual process of synchronizing the carbs is the easy part assuming you haven't burned yourself yet. With the engine running and the little things in the carb tune bouncing around like jumping beans, you're ready to go.
  • This is how my gauges looked like when I started. My engine was warm and was idling normally.
  • The horizontal lines across the Carbtune represent increments of 2cmHg. That's 2 centimeters of Mercury.
  • Carbtune and the shop manual say to get the top of each column within 2 cmHg. That may be ok for the shop ape, but I spent good money on this sucker and took some time to get it all set up. It only takes about 2 minutes to do what you really came here for so take the extra minute and get it as close to perfect as you can.
There are 3 adjusting screws (not 4 as I would have suspected). One sits between carbs 1 & 2, another sits between carbs 3 & 4 and finally, another screw sits between carbs 2 & 3.
  • I adjusted the screw between carbs 1 & 2 first and got the gauge columns as close as possible. The screw needs very little adjustment.
  • After each adjustment, blip the throttle and give the gauge half a minute to settle down; re-adjust as necessary. Deepthroat says don't blip too hard with mercury gauges; if you do, you stand a chance of the carbs inhaling a little bit of mercury. Undoubtedly, that'll work its way through the system and end up in the air for you to breath in. Like I said, don't blip the throttle too hard with Mercury gauges.
  • Occasionally, I made sure the Carbtune was sitting straight up and gave it a little tap on the back if it looked like one of the columns wasn't jiggling about.
  • Next, I adjusted the screw between carbs 3 & 4 being just as fussy as with 1 & 2.
  • Finally, adjust the screw between carbs 2 & 3. This simply sync's the left pair to the right pair. You'll want a really long Philips screwdriver for this one. A slot will work but it tends to jump around on the screw head.
  • According to http://www.motorcyclistonline.com/howto/howtocarbs/ :   "As a final test, run the engine up to a low cruising rpm and see how the vacuum signals compare. (If they're way off now but fairly equal at idle, you may have a sticky slide, sloppy linkages or some other malady and syncing won't help.)"

When I was done, this is how the Carbtune looked.

This was my first time at the job and if I can get them this close so quickly, why should you settle for anything less. Now I'll see if it took any of the buzz out.

It's time to let the bike cool, remove the hoses, replace the bike's hoses & plug, replace the gas tank, apply some burn cream, and go for a test ride.

Here's another idea on a gas source while you're doing the job courtesy of Jay Franks, COG#5692.

  • Use any flexible plastic container with a sealable cap that is large enough to drill two holes into. (The cap, not the container.) I used a poly bottle about 3" in diameter and 6" deep.
  • Drill one hole that will be a tight fit for the piece of tubing  you will use to connect the bottle to the carb fuel hose. I selected a 5/16" O.D. tube that will fit into the 5/16 I.D. carb hose. Drill a smaller vent hole in the cap also.
  • Push the hose into the bottle cap so that it reaches almost down to the bottom of the bottle and fill the bottle about 1/2 with gas. Place the cap on the bottle and hang or wedge the bottle, WITH THE CAP UP, somewhere that is convenient and above the carbs. When you are ready to start the carb adjust, place your finger over the vent hole and give the bottle a slight squeeze. This will start a gravity siphon and the gas will feed until it runs out, or you break the siphon. To do that, you can lower the bottle until it is below the carbs and remove the tube from the carb hose and the gas will run back into the bottle.
  • No valves, no leaks, simple to make, and Cheap!

Article By: David J. Morrow

Updated September 2007

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