Ken, the only thing that changed from left to right was the caps... and the issue followed. Your caps are where the issue is. The vent tube adds a slight pressure to the tank. If the vent tubes are not aligned into the airstream, one tank will get more pressure than the other, thereby increasing the flow out of that tank.

The only other thing that could be different is the flow of air through the vent tube may not be the same due to a partial blockage, either debris or the hole through the cap is not the same size, or some other restriction.

Hope this helps.

Ralph