The only way I know to reduce weather helm is by raking the mast forward. By raking the rudders forward you can remove the symptoms, but the boat will still not be in balance.

A certain degree of weather helm is desireable, but not more than 1 or 2 degrees.
If your jib is sheeted too loose and main too tightly, you can also get excessive weather helm. Crew position also affect weather helm, and this can can change for different windspeeds. But not enough to make it a problem.
Some designs like the Hobie16 load up their rudders a lot to make up for the lack of centerboards/daggerboards, so if you sail one of these designs, you would have to accept the mast rake and remove the symptoms by raking the rudders forward instead. If you lack adjustment screws on the rudderheads, you might have to re-drill the rudderblades.
We have had lots of discussions on the open forum earlier, so a search will surely yield results.