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Carb sync...I guess it's a mountain!
There are a lot of posts about carb syncing. A few more about sync tools. So I'm not going to go through all that info again. <!-- l --><a class="postlink-local" href="">viewtopic.php?f=56&t=2975</a><!-- l -->
A member of this forum was having a hard time syncing their carbs, even after reading Bluewing's post in the "tech center". <!-- l --><a class="postlink-local" href="">techcenter/article1000.htm</a><!-- l -->
Great pictures, Lane!

But before I tell you the easiest way I've found, I'd like to clear up a few "misconceptions".

Number four carb isn't adjustable. I hear this over and over from very knowledgeable people in the industry. Well guess what? Number three isn't adjustable either. Neither is number one or number two.
When you syncronize your carbs, you are changing the opening of the throttle plate[s]. That's it.
You're not changing the mixture or the air to fuel ratio. Those are all designed into the carbs by use of fuel jets, air bleeds and emulsion tubes, and the idle mixture screw. The only way you can affect the air/fuel ratio is by altering the float level. Closing off or opening up passages that affect mixture.
When you adjust the sync screw on the left side of the bike, it changes the throttle plate position of the #2 carb.
When you adjust the sync screw on the right side, it changes the throttle plate position of the #1 carb.
Adjusting the sync screw at the rear of the #3 carb causes BOTH the right side throttle plates to change, since the are linked mechanically.
Well, what about #4? Number four throttle plate position is adjusted by the idle stop screw. Since all the carbs are linked, all throttle plates move in unison.
You don't sync number one to number four because number 4 isn't adjustable. You sync #1 to #3 because that is the linkage that's intended for that purpose. You sync #2 to #4 for the same reason. You sync right to left for balance and set all to a specified idle speed.

A lot of people have a terrible time syncing their carbs because they make it WAY TOO HARD.

Who cares if number four isn't adjustable? How do you sync just number 3 to #4? Does it help if I turn my head and cough? Forget everything you've heard about syncing carbs. There is a very simple method to syncing the carbs, provided the rest of the systems are operating correctly.

1-set your base idle speed to 1000 rpm.
2-adjust #1 to #3 [or number two to number doesn't matter]
3-adjust #2 to #4 [or number one to number still doesn't matter]
4-adjust balance right to left [or left to right]
5-run the throttle to @3000 for a few seconds to clear the cylinders and return SLOWLY to idle.
6-reset base idle to 1000 rpm.
repeat until you're satisfied. Shouldn't take more than a couple repetitions. The entire job shouldn't take more than 1/2 hour. Including removing and replacing the lowers.

Hope this helps. I understand doing something the first time can be time consuming. It is for me. But once you've done it, you'll scratch your head and wonder what all the ruckus was about.
#1 04-08-2009, 08:54 PM,
Good stuff GL...
The way I did mine (when the carbs were off the bike) was to use a very small drill bit as a gauge... I first set the idle speed screw to the drill bit, then made all the other adjustments (using the drill bit as a gauge)... If one takes just a bit of time and uses a small enough bit, the carbs can be matched to within a thousandth of an inch... Once the mechanical components (butterfly valves and float levels) are all exactly the same, is the only time one can proceed to the operational side of things (air mixture adjustments)...
Ed Zogg
#2 04-09-2009, 06:33 AM,
Makes perfectly clear sense to me GL. Thanks for laying it out for the folks here.
Ed (Vic) Belanger - 1954-2015
Founder of

#3 04-09-2009, 09:32 PM,
I connected my spankin' new Morgan Carbtune to Miss Patina during spring re-commissioning - found left side cylinders out of whack with each other, and right side fairly even but way low compared to left side. 3/4 of a beer later (don't panic there was no test ride - much bodywork was off the bike for spring inspection / rag wiping) the engine was idling much "easier" - the readings very even to each other - the later test ride proved to be very pleasant - a very noticeable difference in performance. Well worth it. As a side benefit it would appear fuel economy has improved a bit. 8)

#4 04-15-2009, 04:34 AM,
Well done. :-bd
Ed (Vic) Belanger - 1954-2015
Founder of

#5 04-15-2009, 04:58 AM,
Very nice explanation,
The first time syncing my carbs , I was a little concerned about getting them all out of wack. It took a little time but posts like this one explaining what is actually happening should take the worry out for others.
I agree about the first time taking a little longer but I'm still not good enough to do it in 1/2 hour with r&r the panels.
#6 04-15-2009, 07:03 AM,

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