Carb sync question

[Alan Schlosser]

Let's see if I can ask this without confusing even myself

The Suzuki shop manual states to sync at 1750 and have 2 and 3 a half ball lower (which has been assumed to be 1cm of mercury.

Clymer states the same 1cm at speeds of 1500-2000, so that's about the same.

BassCliff's tutorial shows the Morgan Carbtune (which I'll be using) adjusting at 2000 and the settings at 24cm for 1 and 4 and 23 for 2 and 3, which again is about the same 1cm difference.

But his link to Mr. Bwringer's carb sync instructions says to adjust at 1200rpm and look for 28.5 and 25.5 respectively, which is a 3cm. difference.

So, what do I do? Adjust for 1cm. difference at 2000, or 3 cm difference at 1200? Or will the difference at 2000 match the reading when the idle is lowered to 1200?

[bwringer]

I've never been able to tell the slightest difference when adjusting these with the center two a bit lower, so these days I adjust them all to the same readings.

The tutorial posted on my site was created by someone else (he's given credit at the top of the page). He also specifies a certain vacuum reading, which is somewhat incorrect. The vacuum reading is not important, only that they are all the same.

The RPM you should use to sync is variable according to taste as well. I prefer to adjust at or close to idle speed in order to create the smoothest possible idle. To do this, the engine must be at operating temperature.

However, some folks feel that you should sync at 2,000 rpm or even higher (I've heard 1/3 of redline) to create the smoothest possible running at road speed (yes, sync changes a good bit at different RPM -- nothing's perfect in this world, including GS engines). If you sync at higher RPM, you'd better do it quickly so the engine doesn't overheat.

[BassCliff]

Hi,

Yep, it's not really an exact science. There are tolerances. Since you have your own Carbtune you can experiment a little and use what works best for you and your bike.


Thank you for your indulgence,

BassCliff