Home Made Carb Synch Setup

The original idea came from PowerChutes but it was expanded and evolved at the Airheads Beemer Club


The manometer consists of 3/16" plastic tubing, red Automatic Transmission Fluid (ATF), about 3 ft. of scrap wood, and a few bits of bicycle inner tube to hold it together. No calibration is necessary 'cause you're just trying to adjust vacuum to be equal. This setup can measure about 36" of ATF vacuum difference, or about 2 3/8" equivalent of Hg vacuum difference. Two cm Hg is supposed to be the maximum vacuum difference between carbs.

If the cylinders are severely out of whack (> 3" Hg difference), the ATF will continue to rise and eventually flow into one carb - quickly pull off the tubes and shut down the engine. Then it pays to crudely synchronize using a vacuum gauge on each cylinder before using the manometer.

You can synchronize 2 carbs at a time with the differential manometer. The other two nipples should be capped.

Turn the engine off to move from one pair of nipples to another. If you don't, when you remove one tube, the lovely red ATF will get sucked into the other carb.


I also blatantly stole the siphon gas holder idea from Jay Franks, COG#5692 (down a the bottom).

In my case, it's 3/16" tubing stuck into the top of a bicycle water bottle, with a little hole drilled into the top. To start gas flow, you cover the hole with a finger, squeeze the bottle 'til gas fills the tube, then release the hole. To stop gas flow, lower the bottle below the carbs.


I used a total of 20' of 3/16" clear tubing, 16' for the manometer, 4' for the temp gas tank, total investment of about $3 CDN. The ATF was left over from changing the rear shock fluid.

The good thing about the 3/16" tubing is that it fits over the Concours vacuum nipples and press-fits into the 5/16" gas line to the carbs.

I know this works, it's extremely accurate, and it's frugal, which rests well with my Scottish blood.