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Carb Sync...Mountain?, or molehill.
An internal combustion engine is nothing more than fuel driven vacuum pump. The greater the vacuum, the better the efficiency. When you attach the sync tubes and watch the gauges/manometer, you are monitoring the efficiency of each cylinder. If all cylinders where exactly the same, and the float levels, throttle plate opening, idle screw adjust, and main jet needle were all the same, there wouldn't be a need to "balance" the carbs. But they're not, so we have to. Just keep in mind that syncronizing your carbs is simply "fine tuning". If radical adjustments are required, you probably have a more serious issue.
So just what is it you're doing when you "sync" your carbs?
You're adjusting the throttle plate opening to achieve an equal vacuum between cylinders. You're not adjusting the mixture, you're not changing anything except the amount of engine vacuum that's allowed to operate on the carbs.
Remember, #1 effects 2, 3, and 4. #4 effects 1, 2, 3 ......etc. When you mess with one, you mess with them all. You don't run up to 3,000 rpm to do an adjustment. You raise the rpm to clear the cylinders so you can get an accurate reading the next time you return to idle to sync them again. And trust me, you'll have to sync them again. And again. It's a process, not a procedure. Sync, rev, sync, rev. Once you've completed the entire process, you should find that the gauge/manometer readings are just as close at 3,000 rpm as they are at idle. If they aren't you probably have a more serious issue.
Also remember that EVERYTHING else needs to be in good working order prior to syncronizing the carbs. Plugs, coils, plug wires, resistor caps, air filter, fuel filter, oil level and quality, etc.
Tip: "I get air bubbles in the sight glass, and have to recalibrate the sync tool." No, you don't. Simply remove the vacuum line from the adaptor. This allows atmospheric pressure to act on the chamber, and your bubbles will disappear. Reattach the hose and you're good to go. Initial calibration of the sync tool is good for the entire procedure.
#1 05-18-2008, 12:28 AM,
fysty-1 Wrote:Thanks for that posting GL. It seem other don't share my appreciation especially the people that live high above sea level. This should be in the Tech section. How bout it moderators? :roll: :roll: Big Grin Big Grin Big Grin Big Grin Big Grin Big Grin Big Grin :twisted: :twisted: :twisted: :twisted: :twisted:

Well....I live at 2600 feet (not sure what that is in meters :mrgreen: :mrgreen: ) and my guess is he wrote that as a guide for "why did it take you all day to sync your carbs Marty!"

Well to my defense I counter with....I wish he wrote it last well as it was 108 when I did it and I would have to shut down my engine to prevent overheating, let it cool and do it again.

BUT I still synced at 3000 rpm's and not at an idle :cry: :oops: :cry: so my guess is that he will PM me and ask me to DO IT AGAIN!!!! Not to mention the fact that I already invited him to Vegas to work on my bike with all the beer you can drink offer. BTW the offer still stands!!!!

While VERY educational I want to leave the tech section to "how do I fix it" step by step.

Thanks for the post!!!
#2 05-22-2008, 05:32 PM,
Beer, I better come along and supervise. 8) 8) 8)
#3 05-23-2008, 03:32 AM,
I don't think it would be a good idea to go into business with Lance. He'd drink up all the profits Confusedhock:
#4 05-23-2008, 07:19 PM,
I have performed the carb synchronyzation process on many GL1200s and it has been my experience that I have had to synchronyze the carbs at higher RPM's, 2500 to 3000 PRM's as well as idle, to end up with a good running engine. Worn linkage and worn throttle plates could account for this variance and splitting the difference between idle and 3000 RPM will sure make your bike run a lot better. Each engine will have different characteristics and dynamics and you must do whatever it takes to make it run properly if you're a good tuner. ONE BIG CAUTION: When making adjustments at higher RPM do not snap the throttle closed or else you will suck the mercury or liquid right out of your manometer. Close the throttle slowly and gently to prevent losing the mercury.
Ed (Vic) Belanger - 1954-2015
Founder of

#5 05-27-2008, 06:00 AM,
Quote:I have performed the carb synchronyzation on many GL1200s
hmmmm...Vic you drink beer? :mrgreen: :mrgreen: :mrgreen:
#6 05-28-2008, 06:23 AM,
vic,.. maybe it's time to have a maintance weekend, where others can be shown the correct way to do things, ie, fork seals, fork oil, sync carbs, brakes, like a meeting of all the great minds. :roll:
[Image: Roadawggoldwings-1-1.jpg]
#7 05-29-2008, 04:53 AM,
That's probably not a bad idea at all. We're having a get together Niagara Falls, Ontario on August 30 and 31 and it might be nice to incorporate something like that into the meet. Good idea.
Ed (Vic) Belanger - 1954-2015
Founder of

#8 05-29-2008, 06:29 AM,
roadawg Wrote:vic,.. maybe it's time to have a maintance weekend, where others can be shown the correct way to do things, ie, fork seals, fork oil, sync carbs, brakes, like a meeting of all the great minds. :roll:


Lets have it at MY house! :mrgreen: :mrgreen: :mrgreen:
#9 05-29-2008, 08:48 PM,

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