TOPIC:

The bench/mechanical sync is to get the carbs to a rough starting point before installing them on the bike. Once on the bike you sync them with the vacuum meters to get them perfect. It also positions the slides correctly in regards to the idle screw setting leaving you with the right amount of room to adjust them into sync. If that makes sense. I'm not too great at explaining things.

tw, you may be right. However, isn't WG talking about the throttle slides? They all need to be in the same position? I guess what I'm asking is, is a bench sync and a mechanical sync the same? They both have the same objective. Even throttle slide height, right? My book say's the mechanical sync is done while the bike is running, taking the top off of the carbs and adjusting the throttle slide to obtain even vacuum, then to the vacuum sync. I think. Anyway, my book doesn't mention a "bench sync" only mechanical and vacuum.

tw.. wrote:

I may be wrong Vach, but I think WG is referring to the sync on CV carbs and your talking about the sync on VM carbs.

Someone please chime in if I'm incorrect.

Post edited by: vach, at: 2007/04/27 13:38

BSKZ650 wrote:

did you calibrate the mercury first?

use a couple of tees and use one cyl, make sure they are all the same

BSKZ650 is right. The gauges can be way off from the factory. The restrictors need to be normalized first. Use a couple Tees or you can actually get a 4-to-1 manifold that works great for like $1.99 at some auto parts stores.

You connect the 4 lines to the manifold, then the manifold to one cylinder. That means all 4 should read the same. If they don't, you need to adjust the weaker ones by tweaking the restrictor. This ususally means poking the hole on the restrictor slightly larger with a sewing needle. It's very sensitive so be careful and use small adjustments.

Also make sure all four tubes are the same length and the restrictor should be at the bike-end of the tubes, not at the manometer-end.

vach wrote:

tw, you may be right. However, isn't WG talking about the throttle slides? They all need to be in the same position? I guess what I'm asking is, is a bench sync and a mechanical sync the same? They both have the same objective. Even throttle slide height, right? My book say's the mechanical sync is done while the bike is running, taking the top off of the carbs and adjusting the throttle slide to obtain even vacuum, then to the vacuum sync. I think. Anyway, my book doesn't mention a "bench sync" only mechanical and vacuum.

A bench sync is typically done off the bike usually after a carb the carbs have been pulled apart or rebuilt. It's a good way to get all carbs set equally before re-installing on the bike. Once installed then you can do the mechanical setting, per the manual directions, while the bike is running.

I hope this helps.

You bench sync carbs on a bench and sync carbs while the bike is running using manometers or other vacuum gauges attached to the carbs or carb holders via vacuum ports.

The BENCH SYNC procedure is necessary on carburetor assemblies with manually actuated slides. It is necessary to preset the slide heights to where they are in the center of the idle knob adjustment range AND get them close to each other. This MUST be done before putting them on a bike and attempting to sync them if the carbs have been apart; that is, the throttle rod has been removed such as for changing jet needle clip position or more extensive disassembly for cleaning, etc.

On CV carbs, bench sync isn't really needed. If you have them apart, it is a good idea to loosen the locknuts on the adjusters and with your eyeball ensure all slides open at about the same time to make sync easier but the throttle butterfly on a CV carb is open just a tiny crack... You SYNCHRONIZE the carburetors once they are on the bike. If your manual calls this bench synchronization, they use the term differently than I have heard it used.