I had seen lots of descriptions for DIY carb sync devices on the net, but they were all for 2 cylinder bikes.
I wanted one for my 4 cylinder VFR 750 so I made one with 4 vertical columns of water mounted on a board.
The columns are about 2.5 meters long and joined at the bottom. There is about a 1 meter water in each coloum.
The columns are mated to 4 tubes that attach to the carb vacuum ports. Here I am using the device to sync the carbs
on my 96 VFR 750.
The device was very easy to build and fairly easy to use. The
difference in the height of each water column gives the difference in
vacuum for each of the carbs. You adjust carbs 2-3-4 until all 4 carbs
show the same vacuum. Carb 1 is a reference and has no adjustment
point. With a bit of carb adjustment I could get the 4 carbs to show
about 50-100 mm maximum difference in the water column levels.
This converts about 100/13.6 = about 7 mmHg which is (I think) close
enough, at least for now. The carbs weren’t all that bad in the
first place (about 22 mmHg max difference which was when the pic was
taken) so there wasn’t any really huge difference in
performance. Here is a movie of the degree of balancing I was able to achieve reasonably easily.
One day I may try to improve the device later by providing damping in the vacuum lines. This makes the changes in water column height happen more slowly and should make the device easier to use since the variations in vacuum should be evened out.
Doug Eleveld
deleveld@dds.nl