Woody,
On a blow through carb you don't need to modify the power valve reference. However if you want to control the fuel better you do that modification, and change the power valve as I stated in my post.
The modification in your post is for a draw through carb, this is how you get the correct reference to the power valve, if you don't do this the power valve shuts off the fuel from PVR channels because the original power valve works off the loss of vacuum to open the valve and on a draw through at top RPM you can get a vacuum under the carb.
Hope this somewhat clear.
Harry
