Stock relief pressures should be between 4.5 and 4.6 psi, most relieve down at 2.2 to 2.4 psi, and need to be adjusted.
I made a fitting to check the pressure relief, took an
oil pump end hose banjo bolt, two aluminum washers and a nut, installed same in
each line, one at a time, and connected my pressure tester.
I evacuate the line of oil, then hold the valve end near my ear, so I can hear the air pressure relieve when the valve opens. reading the pressure when the "air" changes gives the relief rate.
To adjust, unscrew the valve parts, remove the spring and GENTLY pull it apart, A VERY LITTLE AT A TIME, put the valve back together and retest, stretch, test until the correct relief pressure is attained, tighten the valve, go to the next one.
Edit: I cannot stress enough to go very slow and gentle in stretching the spring, it is very touchy and small, and can be super easy to damage/destroy.
Edit: I set the blowoff pressure to 4.6 psi, that way, I figure the spring will sack back to 4.3/4.2 psi when it gets happy once again. When rechecked after being run a few thousand miles, the spec of 4.3/4.2 comes in steady.
Using a hose and oil can filled with two stroke oil, connect the oil pump end of the line with the pressure check bolt in place, and GENTLY fill the line, return it to the bike, bleed and go. Stops down the time to fill the whole line from the oil pump, and you won't need to use premix to bleed the pump/lines.
My Bridgestones all have valves that have hose bibs and use rubber hose between the pump and valve. I will look, as I think there may be more bikes that use that type of valve setup, like a few Suzukis and Yamahas of the past. Most Suzukis used a hard line plastic line like our stuff has.
There may be fittings available in generic form for the oil pump end from companies like McMaster-Carr, which has a web site, don't remember the address right off. 6mm bolt hole will relate to 1/4th inch (.250) in non-metric sizing. I'll have to go with the rubber hose when I case reed my next engine, as the oil injection inlet will be in the front of the cases, with the reeds.
Kawasaki specifies 4.6 psi blowoff pressure.
Since there is a metering orifice in BOTH the bottom of the banjo bolt, for the crank, and in the oil passage in the inlet port, the reversion pressure is dampened, so the differential backwards doesn't adversely affect the check valve. Lower end vacuum/pressures are at the 1.50 to 1.75 psi range, lower than the check valve blowoff pressures.
I have checked new valves out of stock at KMC, Santa Ana, when it was still there, and got between 2.0 and 2.9 psi.
We got in trouble one time for blowing the check ball all the way through the spring to the other end of the valve on F series valves from the 125 psi pressures from the air hoses we used to break 'em, Japan didn't think it was funny, and that is where the Kawasaki failure code "OU812" came from.
I worked for Kawasaki for 4-1/2 years, stretched many,
many A, S and H series check valve springs, which corrected over-oiling, along
with setting the pumps up correctly, and never had ONE failure of the valve,
spring, seat, ball, NOT ONE. Never seized an engine after adjusting the oiling
system, once again, NOT ONE.
Without redoing the check valves, oil mileage for a tank of two stroke on the typical 3 hose system on an H2 would get 500/600 miles with the pump cable set correctly, with the revised check valves, 900 to 1,000 miles per tank, with no seizures.
I'm just putting ideas out, nothing more. If a valve is more easily made on a CNC machine, and for a reasonable price, well, that's the way to go. If ones are available that are either right or can be made right for low dollar, or no dollar, fine. Of course, CNC time is expensive, no-one is disputing that.
I just don't like all the "specialty" triple "guru's" getting hold of this kind of thing and charging out the kazoo for it. This is a sport, hobby, not a "buy me a house, buy my stuff" kind of thing to me.
I see regular everyday parts way overcharged to users every day on the automotive sites I visit, reboxed, manufacturer I D obscured just because someone wants to charge three times its real worth, than from the NAPA store the very same part actually is available from.
The converse to all this is stuff like Tomcat pipes, which are hand made, darn good and worth every penny, because one person is putting his all into making something from flat sheets of metal, not outside buying something for excessive profit.
Please don't get me wrong, if an aftermarket check valve is available for a reasonable price, and fits the specs, then we need to let everyone know, so they can get 'em if they need 'em. Now, let's go find that valve.