Mickey try this, remove the air filter cover altogether and replace with 2 very wide washers to hold the filter in place.
Now take it for a spin and see if any change, I've discovered by checking out other sites and mucking
around with my 79 that they don't breath at all well.
This can't hurt and if it detracts from performance you can just slap the cover back on no harm done.
The system may have been set up to restrict the bikes performance as a gas saver during the petrol crisis, same reason my speedo only goes up to 80mph to try to trick me into believing any 650 worth it's tires couldn't crack 100mph.
Not sure how much water she will swallow if you get caught in the rain again, we don't get a lot of rain around here.