As I mentioned before, We used to balance the carbs by lifting the plug caps. This is not allowed any more and a bike that has any after market electronic ignition can blow the ignition module part of the system by lifting the plug caps. You must use the short 4 mm rods on the spark plugs to short each side out in turn to balance the carbs. These rods should be tightened with a wrench because they will vibrate loose if not tight enough.
A too low an idle will cause an oil starved engine. It can ruin the lower end of the engine. A too low an idle will ruin your day. I believe the lowest idle in the book is 6 or 7 hundred. These are quit low. Most riders today have idle set around 1000 on the R90s. Mine is a little below 600 I think.
I'll be back.