Davida vacuum gauges

[Laverda Dave]

Hi All,
I bought a second hand set of Davida Vacuum gauges a while ago to replace the steel rod Morgans that were never unfortunately as good as the mercury ones I had years ago and sadly got broken.
The Davida's didn't come with any instructions but I didn't think that mattered as I've used the mercury filled Morgans well in the past.  The problem I have with the Davida's is the reading scale, the increments are in lbs and not hg.  The scale reads from 0-0.6lbs.  According to the Haynes manual a reading of between 16-24hg is required during carb sync, there are no alternative lb readings provided. Checking a conversion chart on the web 16-24hg = 0.6-0.8lbs?  This will be off the scale on the Davida's 
Does anyone have a set of Davida's and can you give me an idea of where on the lb scale the carbs should be balanced at?

[BigAl (Alan)]

I had the same issue a number of years ago with new gauges (as image) and instructions when I set up the CB750.  I simple carried out the instruction 'synchronisation is obtained when the vacuum is the same on all gauges'... it worked.
Never got to the bottom of 1bs = Hg ?

[hairygit]

Al hit the nail on the head, vacuum pressure is irrelevant to our bikes, getting all the carbs as close as possible to identical readings is the aim, hence "Synchronizing the carbs"

Sent from my X6pro using Tapatalk

[Deano400]

16-24 mmhg would give 0.31 - 0.46 lbs (PSI).

[flatfour]

I've used Davida's for some 25 years on a variety of bikes (mainly four - cylinder Honda's though) and the needles always sit at around the Five - to the Hour position as on a clock face.

With the exception of a need to replace one vacuum hose after around 20 years of used (collapsed) the gauges have been faultless.

[JamesH]

Video screen shot of a Cb750 K5 at idle (#2 not yet balanced) using davida gauges

[JamesH]

Word of advice - I wouldn't try to aim for 'absolute' numbers, just aim to get all 4 in sync.

[Laverda Dave]

Thanks for the advice everyone, I aim to get the carbs balanced over the next couple of days. I'll report back (carb overflows permitting!).