After doing a review of the regular 42 on a 40 a year ago, we got a chance to test a L version on a new 40. I purchased this cutter several months ago but due to schedule and weather haven't had a chance to hook it up and test it out.

The VMC brush cutter.
https://vmcequipment.com/ourproducts...

As a viewer pointed out in the comments, there is a 1 or 2 way circuit selection valve. An image of it can be found on page 54 of the KX040 manual. Turning the value for 1 way circuit can relieve back pressure. However, if you turn this, make sure to turn it back when you go back to using your thumb or any aux which is 2 way.

TOC
00:00 Intro
01:05 Hydraulic lines and proper rotation of the cutting blades.
05:45 Outside view cutter cutting bank and extended
08:51 Cutting small scrub
14:07 Cutting 3 to 4" tree
16:24 Trimming trees in mowing area
17:33 Final Thoughts on this model vs the EXG42