Syncing with homebrew carb gauge

[kar_the_terrible]

Hi,
Im syncing my carbs with a homebrew carb gauge ... clear tubing and oil. Now I can sync the carbs just fine on idle... I can bring it to within 4 cm of oil level. But the problem is that when I rev up the engine, the oil level sits steady for sometime and then suddenly starts to rise up in the direction of one carb.

Are my carbs falling out of sync? the direction of oil level change is consistent towards the left carb, Im just not sure if the low density of the oil instead of mercury makes any difference... and whether the gauge can be easily destabilized, even if there is a momentary vacuum difference between the carbs.

thanks
-Kartik

[old-n-slow]

I would be inclined to look for another cause. Something like vacuum leak between one carb and the engine. A filter (if each carb has separate filters) that is dirty, a difference in compression between cylinders.