Couple people I've ridden with have commented on the great gas mileage the Vara gets and I may have discovered one of the reasons. I had to change the air filter the other day and see that they have a damper actuated by a vacuum dashpot in the airbox.
Seems that in cruise mode (full vacuum) the damper will be closed reducing the airflow to the filter, O2 sensor will see it's running rich and ECU will back off the fuel, presto changeo instant economy mode.
When you need to "give er" and slam open the throttle of course you lose vacuum, the damper opens, more air gets in, O2 senses lean, ECU gives it more gas, presto changeo instant power mode....
Or at least that's the way I figure it works... Whatever I get a good 55 MPG and over 400 kms on 20 some odd liters of regular gas.
Maybe others work that way to, I don't know but I like it!!