Yes you need to increase the size of your leader. Here is a suggested chart showing leader to fly size: This is just a rule of thumb chart, different leaders will handle different sizes of flies.
For some reason unknown to me I can not seperate the data below, I do and when I save it everything jumps back together.
The first number is the tippet diameter (.003)
The second number is the tippet size (8x to x4)
The third number is the pound test of the leader (1.2 pounds to 18 pounds)
The last series of numbers are the suggested fly size (24, 26 28 etc)
Tippet Diameter Tippet Size Pound Test* Fly Size
.003 8x 1.2 24,26,28
.004 7x 2 20,22,24,26
.005 6x 3 16,18,20,22
.006 5x 4 14,16,18
.007 4x 5 12,14,16
.008 3x 6 10,12,14
.009 2x 7 6,8,10
.010 1x 8.5 2,4,6
.011 0x 10 1/0,2,4
.012 x1 12 2/0,1/0,2
.013 x2 14 3/0,2/0,1/0,2
.014 x3 16 5/0,4/0,3/0,2/0
.015 x4 18 6/0,5/0,4/0,3/0
However, what you have to remember is that there will come a point and time when the fly will overpower the fly line and rod. A 5 weight rod and line can only handle a certain weight of fly before it fails to load properly and your cast will disintegrate rapidly. Then you have to go to a heavier rod and line.
Larry
—sagefisher—