I picked up a (I know) Century R1A1 for a song. The owner said it had cycling issues.
Upon inspection of the rife I noticed the gas regulator sat too far back hitting the hand guards and not effectively adjusting the size of the relief hole. I removed the hand guards and screwed the regulator on further so as to actually adjust the gas relief. My question is how far is the regulator supposed to be screwed on? Until it contacts the front sight post?

I screwed it on till it stopped, then backed it off 1 revolution till the #1 setting just did cover the hole.

Yes, close it up and then shoot it, if it won't cycle then you have other issues.

FYI, what ever you do, do not break that regulator ring.  They are impossible to find if you do, it will not fit, you will have to hand fit them.

I had an R1A1 cut down to 14"+2.25" brake, I had to run it on 1 or 0 to get it to cycle.

Thanks, I hope I'll be pleasantly surprised when I get to test fire it.

Once you determine that the rifle functions as a previous reply has recommended you want to open up - lower number on the ring - so that it is not slamming your rifle internals.  The purpose of the adjustment is to handle "adverse conditions" as in dirty and it is time expedient to continue operation of the rifle until such time as you can clean it properly.  I would open the port to around 2 or 3 and test fire the rifle.  The goal is to adjust the gas to the point where the rifle consistently feeds and fires reliably.  I would then use the next higher number on the regulator.