DragBikeMike has convinced me to change to a smaller orifice and get a bit more oil pressure.

The current orifice was made with a #56 drill that has a diameter of 0.045" and is roughly equivalent to a #120 main jet.

I made another orifice using a #57 drill that has a diameter of 0.043" and is a bit smaller than a #115 main jet (but bigger than a #115 jet).

While a change in diameter of 0.002" doesn't sound like much - the area change is noticeable.  A 0.045" diameter hole has an area of 0.0016 square inches.  The 0.043" diameter hole has an area of 0.0015"square inches.....the change is a 9% reduction in area.

I will make another test ride and see what affect the smaller jet has.  The next size drill I have is 0.042" in diameter - which is likely another 10% reduction in area.

Using very tiny drills on a lathe with a 12" swing is a bit intimidating...it would be so easy to snap the drill if I put too much load on it.  I used a high turning speed, lots of oil, made very slow advances and backed the drill out repeatedly to get more oil in the tiny hole.  

I went for a ride with the new smaller orifice.

The change was small.

With the previous orifice the oil pressure at idle was a bit over 1psi, and the 3,000 rpm pressure was 6psi.......the 4,000 rpm pressure was 8psi.

Now the oil pressure at idle was up by 1psi to 2psi, and the 3,000 rpm pressure was at 6psi which is unchanged.......the 4,000 rpm pressure was up 1 psi to 9psi.  I wound the engine up to 6,000rpm and the oil pressure was right at the 15psi limit of my gauge.  (It seems a bit weird the 3,000 rpm pressure did not go up 1psi like the idle and 4,000 rpm pressure did....I ran at 3,000 rpm for an extended period and it was locked in at 6psi).

I went ahead and made another orifice with the #58 drill, which is 0.042" and equivalent to a #110 jet.  This is likely the smallest hole I can make in the steel screws I have been using to make the orifice....the tiny drill wanted to bend when it was first starting the hole (I had made an initial center point with a larger drill to make it easier for the tiny drill to get started easier).  If I need a smaller hole - I might have to switch to brass or just buy jets and thread the outside to fit.

I will go for another test ride as the weather and chores allow.