Thread: Syncing carbs.

How did this thread turn to syncing Webber carbs, or even butterfly carbs for that matter. The video clearly shows an XS650 motorbike fitted with VM 'slide' carburetors. For the third time I feel it important to stress, the carbs in the video are 'slide' carbs.

There are dozens of different type carbs and many methods of syncing them. Making a video on syncing carbs is individual to a particular brand or type. This video obviously deals with syncing Mikuni VM34 carbs, as fitted to the bike and as shown in the video. Absolutely nothing to do with Webbers, Delortos, Amals, Carters, Bendix, Pope, or any other type of carburetor.

The XS was fitted with CV carbs throughout its production, however, syncing them is basically the same as with the VM 'slide' carbs: Sync them at idle using the idle adjustment screw, then sync them when the slides or butterflies are clear of the idle screw stops. This is standard practice on this bike, as it is with plenty of other bikes.

The second picture I've posted show the VM 'slide' carb with an idle screw and a throttle adjustment screw, they are not linked: The idle syncing is controlled by the idle screws. Throttle syncing is via the adjustment screw on top of the carb.

The second/fourth picture is of a set of BS38 CV carbs, similar to VM carbs, the idle syncing is done via the idle screw, throttle syncing is done via the screw between the two carbs, this screw synchronises the opening of the butterflies.

The first picture is of a single BS38, early XS650s did not have the carbs linked. Idle syncing is done via the idle screw, throttle syncing is done via an inline cable adjuster screw, as on many bikes. However, the picture shows a modified carb showing a throttle adjustment screw fitted to the top of the carb, the idle screw is also shown.

So why didn't I title the thread 'syncing Mikuni VM34 carbs'? Simple, the video shows the type of carb being synced, and, all my posts have dealt with building and modifying an XS650 motorbike, why would I suddenly switch to VWs or Holdens.

Late on the scene here, but:

I ride BMW Twins and have tried a couple of different methods over the years.

These are getting harder to find now, but, I use 2 economy gauges out of XD-XE Ford Falcons....remember them?....lol
Mounted on some ply with a DIY manifold piped up to them.
The gauges are great. Good range and inbuilt damping. manifold allows me to run both gauges off one side to spot check calibration. never had an issue.

I like them so much I'm bought a couple more off ebay, in case I get a failure.....lol

I also use them on my R1150RS ( throttle bodies ) they still work well. had a slight difference, adjusted it and instantly noticed the different.

Steve

Not familiar with XD Falcons, my interest in Fords ended with the XY/XB. I gather the economy gauges are some sort of vacuum gauge that connect to the manifold.

Originally Posted by Hoggo1951

Not familiar with XD Falcons, my interest in Fords ended with the XY/XB. I gather the economy gauges are some sort of vacuum gauge that connect to the manifold.

LOL...yep.You are old school...lol

Ford Vac Gauge.jpg

A number of car makers had that sort of gauge around that time, usually the same size as the speedo to fill up the dashboard where the idiot lights used to be. A few of the jap cars had a small light up the front of the mudguard that lit up if you planted your foot, all operated off manifold vacuum.

One of the boy-racer add-ons in my youth was the Smiths Vacuum gauge which you were supposed to be able to use to detect sticking valves, air leaks and all kinds of maladies by looking at the needle flickering (all in a 2" die dial). Well it looked the part if nothing else...

But we digress somewhat.

I bought a low cost twin gauge engine vacuum tester.
It looks impressive, but is really only a toy - the needles don't match even when they are both applied to the same test point using a T adaptor.
The good ones cost a lot more, but even these probably should be checked before each use.

Better I think are "stick" type gauges that use liquid in clear tubes, even home made ones.

DIY manometer.

Vac Carb Sync-er (1).jpg Vac Carb Sync-er (2).jpg