I only used the tach on the bike. Actually, I didn't even look at the tach, I just listened for the changes. The pics above with the fuel shown at the carbs, was that only when you rebuilt them 2 years ago?
The plugs are really lean. There is a good chance your jets are getting gummed. With crap gas and any time sitting, these carbs need attention. When I used to run ATF with the gas, (1 oz per gallon) it would take two tanks to get the carbs smooth again.