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.

Please let us know what you see when you change to the OEM filter.  If your pressure changes it will be valuable information.

You are spot on with your comment about oil temp.  I have observed very small changes in temperature making significant changes in pressure.  As I recall, you measure oil temp by shooting your filter cover with a IR thermometer.  I don't think that provides sufficient accuracy for evaluation of the running pressure.  You need real-time data.  Even with a permanently installed thermometer, I find it tricky to nail down a consistent pressure for the observed rpm and oil temp.  It takes a bit of patience and persistence.

Regarding temperature, your observed pressure vs rpm may be lower than mine because your oil temp might be higher than mine.  I'm running a portion of my oil through a cooler (circuit to gear mesh). That most likely results in my sump oil being slightly cooler than it would be on a stock configuration.  In addition, I believe my ambient temp out here is probably a bit lower than yours.

I used to measure my oil pressure off the right-hand side of the head cover, then I switched to an external oil feed to the top end and had to move the oil pressure gage connection to the left-hand side of the head cover.  That's where you are connecting your gage.  When I made that change, pressure at high rpm went up a few psi, and pressure at idle went down 1 or 2 psi.  I believe those changes can be attributed to a less torturous path to the top end (high rpm flow increase) and the elimination of oil-heating in the cylinder and head oil passage (higher viscosity oil at low rpm).

My compliments on the jet machining.  I can appreciate how hard it must be to drill those small holes in steel.

At first I thought maybe the pressure had increased by a bit and perhaps the OEM Suzuki filter was less restrictive - however it turns out that the cooler air temperature and curvy roads on the first part of the ride just didn't get the engine and oil up beyond 230-235 degrees at the exhaust port.

On the way home I did about 20 miles of highway and got the engine up to 245-250 degrees.  I had the same pressures I had on my last ride - 2psi at idle, 6psi at 3,000 rpm, 9psi at 4,000rpm.

I got 59mpg on the last tank of fuel - I think it should do better than that.  I will be installing the A/F meter and checking how the mixture is with this piston - I have not yet done that since installing the Flat Top piston (The spark plug looks good and the bike is running great).

The testing is over - time to take the pressure gauge off and just start riding the darn thing!

I will be installing a low oil pressure switch and idiot light soon.

I worked outside this morning - then after lunch it was just too hot and I retreated into the garage to get the bike work finished up.

I removed the oil pressure gauge and plugged up the threaded hole in the cylinder head cover.

I then installed the 14mm adapter and pressure switch.  The switch activates at 6psi...this was the lowest pressure unit I could find.

The switch provides a ground when the pressure drops below 6psi - so I only needed to run the negative wire from the LED light to the switch.  I drill a small hole in the large center frame tube up at the steering head, and rand the wire down the inside of the tube.  When the wire exits the large tube I used black electrical tape to secure the wire to the right side frame tube - it is pretty much invisible.

This is what the light looks like with the fuel tank mounted and the switch on.  It is a very bright LED and should be easily visible in direct sunlight.

I hit the starter button and the light went out when the oil pressure built up from the running starter (it is raining so I can't go for a test ride).

That oil pressure warning light is totally pro, and it certainly will get your attention.  Very nice installation.

Can't get over the mud stains on your helmet.  Your bike must have been a complete mess after that ride.  My bike is a beater; it definitely looks well worn.  It doesn't get any oooos & aaaahs, but I never have to wash it.  

I think you have pretty much exhausted all reasonable options for increasing your oil pressure.  You definitely have significantly more pressure than the stock system, and now you have a warning light.  Pretty sweet setup.

I've been watching your weather on the nightly news.  You guys have been havin a rough summer.  You are long overdue for a nice stretch of dry, temperate weather.  Can't wait to hear how the cafe shakes out on some long rides.  Very interested in how the flat-top piston works out for you.