I get arm pump pretty bad, but only on my throttle hand. I rode a 2016 YZ450 this weekend and the lighter pull throttle spring (2015-2016) helped a bunch. So with a little searching I found Tokyo Mods. They sell a lighter pull spring for 2010-2014 CRF450 & 250. This spring works on the 2014 YZ450F with some minor modifications.
This is the stock spring.
This is the Tokyo Mods spring as it comes.
These are the two modifications that need to be made. First straiten the hook (red line). Then unwind the spring 90 degrees (green line). Clip the excess wire to make it look like the stock spring. If your not getting enough preload, or the pull is too easy for you, you can unwind the spring up to 135 degrees to taylor it to your liking.
That's all you need to do. To install the spring you just need to take out the one allen bolt for the throttle body cover on the left side of the bike. Then one 11mm nut holds on the throttle cable wheel. Lightly tap the wheel to loosen it. Also, remove the cables from the throttle tube on the handle bar to get some extra slack.
Edited by luckyguy19, October 30, 2015 - 12:03 PM.