A valve on the oil line is often (not always) a sign that the oil pump is worn! When it's worn oil seeps between the drum and housing. Very annoying to find the crankcase full of oil! A fresh pump has a play there something around .0001" or better and normally very little oil is escaping through! The pump and drum is size matched from factory and that is the reason a number (1 to 6) is stamped on the body. Mechanics often doesn't know that fact and there's a risk with mix up disassembled pumps and fit the wrong drum in a body.

The body wears oval and the drum conical. The worm drive is also often worn until the drum cogs are so thin they break, with a cracked pump body as a worst result. And changing cam shaft only is not really a good idea either, they fair better beeing paired. Keep an eye on the camshaft bushes, don't let them wear a too large play or that will wear on the oil pump gear!
Sorry to say it's all an issue as repro oil pump parts or camshafts isn't produced for what I know (hint hint if you have resources or contacts..), and you need good drum cogs for it to be worth hone the body round, rechrome the drum and grind it to specs.

If you plan to take it apart, the end cap is threaded counterclockwise! and it often sits like hell so you'd better have a custom made exact fitting exact parallell full width hardened blade in the slot or you'll slip and make marks, and perhaps it needs some heating as well.  As my cap did sit damn hard, I had to bolt the pump to a square piece of aluminium in order to hold it firm in a vice.

Take notice and write down how many turns the adjusting screw is turned out from the body.
The orig screw threaded part is 19mm long including the rounded top, with the head in total about 22,2mm long and the nut is 3,2mm thick. 
Observe that the original screw and original nut is important to use for the next statement I make. It is risky to give a specific measure as a non original screw or if something else is altered will change the amount of oil deliverd, and because of the oil consumption of the motor in question, but a base measure is 4 full turns out, normally that should give a little too much oil for a newly restored motor, but keep a sharp eye on the oil level in the beginning!  Better is to do like George Yarocki, run it in a lathe at 500rpm, about 18 drops per minute for a fresh motor with 3 piston rings, and perhaps up to 28 drops is needed with old 2 ring pistons..

Adjust in 1/4 or 1/8 turn increments but never more than 1/2 turn at a time and 1-2-3km between checks in the beginning. With the 1928-30 pump, when the original screw head and original nut is together and turned fully in, the pump does not deliver any oil at all. The 1931-32 pump adjustment is different. When you remove the level plug on the crankcase, if it just is dripping or doesn't run any oil, the level is too low in my opinion. I like to have the oil level as such as it runs out about 1/2-1 dl! (1/4-1/2 cup)

A good idea is to take the pump apart before first start. You can find the plungers rusted solid or maybe broken spring(s) (my springs where about .67" long)
The pump doesn't exactly produce a geyser of oil, one drum revolution takes 19 turns of the camshaft! For the 2 tiny plungers (.217" diam) in the drum means one stroke every 19 turns of the crankshaft. The plungers slide against a hardened washer that pivots on a pin ( .127" diam and ~1.130" long) that goes through the body. That measure was given to me, so I don't really know if the pin is cylindrical or slightly conical in order to tight up in the holes. The adjusting screw sets the angle of that washer, thus plunger stroke and amount of oil delivered.

My pump was so full of rust in the front compartment that the washer was rusted solid on its shaft and that meant any adjusting wouldn't work and the motor was at risk of getting too little oil. I poured phosphoric acid in the pump compartment and let it soak for 2 days and it went fine, and a dab of sticky grease hopefully prevents more rust. I didn't need to demount the washer and its pin.  In my used pump, the plungers putrode about 8,8mm and it takes about 2 kg to press one of them in 4mm..

In my opinion the oil level is perfect with 1/4 cup running out..

My view on that is the risk and cause of motor damage is substancially less with too much oil than with too little oil. The risk that the oil level gets too low is a lot greater when the level is on the margin. In the crankcase there is only (i haven't measured exactly) maybe 2dl (a cup) of oil that is churned constantly. The consumption isn't constant all the time, so the level is changing slightly all the time. The oil consumption can increase momentarily if the motor gets hotter than normal, say in a long hill or a stretch of faster than normal riding.

I have not experienced any problem at all with 1/2 to 1 dl (1/4-1/2 cup) extra in the crankcase.

I have experienced  on a couple of occations how the engine reacted with too much oil when the pump wasn't adjusted properly. The motor got hot and hesitant, smoked and protested and when I emptied the crankcase the hot oil spurted out in a jet, I would guess some 3 maybe even 4 dl. The engine was fine after  I drained it.

I also have experienced running with too little oil. On the hometrip from the Int. Indian meet in Scotland, I ran with a pack of Indian guys and in Holland they took, or maybe there wasn't any other choice, a 100 or 110km/h highway. The traffic was fierce with a lot of heavy traffic that averaged some 120-130 km/h and I had to ride a lot faster than my comfort.

Well the 4 lanes in my direction suddenly narrowed to 2 lanes and entered a kilometer long tunnel.  The traffic was insane all around me. Just when I prepared to enter the tunnel I suddenly felt the engine hesitate and I could not do anything about it because there where no road shoulders, no pockets, nothing at all to stop safely on. A kilometer is bloody 1000 meters. It takes 40 seconds to pass in 90 km/h. I had just one choice to try to keep it going as long as possible. The motor became increasingly noisier and slower...After an eternity when I got out of the tunnel, sheered to the shoulder and let off the throttle, the motor struck stop, completly frosen, and the rear tire skid before I hit the clutch.

There was no time to drop the handlebar, bend down to turn on the petcock for the handpump, pull the pump handle, wait a while for the pump to fill with oil and push down the rod. That is insane to even think of risking that in heavy traffic, even more so with an engine on the brink of seize solid and a band of trailer trucks about 10 meters behind in 100km/h.  The handpump was bad anyway.

I can tell you right away that having a bit too much oil is a lot less scary than having a bit too little oil...and way cheaper...

Well, I trailered the bike to "Mr Indian" in Holland, and shipped to Hull so that meet wasn't very far to ride to and fro on the bike. Jeff and many others has probably travelled far more than me. I haven't seen it spraying out the tube, but then again I haven't paid much attention to it at 50 mph :-) No, of course it dribbles and drips and I prefer parking on dirt. But not from the tube. I have made a oil catch can that I have in the toolbox. The catch can has a large inbuilt flutter valve and the tiny tube flutter is discharged with. I got the idea from Daniel Hanasch that wrote an article in the club paper some years ago. I crammed in a small car oil filter in the can, and with the hoses and tubings and rods and shit it's a slobby slippery knuckle busting business to get out and empty.