My mistake. I said power valve, but I meant Idle Jet.
I did speak with Dave Renner, hell of a nice guy.
For those that don't know, on a Marvel the idle jet is the tube that remains in the lower half of the carb and sticks up about 1". This tube CAN NOT be removed. If damaged you can not purchase another idle jet, no one makes them.
The orifice must be between .0225-.025.
Originally I had purchased 2 Marvels on eBay and someone drilled out one of the idle jet holes about twice the size of what it should be. I soldered it up and redrilled the hole. A number 74 or .06 drill does the trick.