I've went through 1st, 2nd, 3rd and 4th gears at high rpms nothing out of the breathers. Only in 5th gear at high speeds. When I hit the throttle instantly oil spews through the breathers and out the hoses/ filter. I've replaced umbrella valves, cam gasket, rocker box gaskets... Compression test were about 10-15# difference, no biggie.
Any other ideas?

 

Don't fill the oil so high. 1/4-1/2 of the way up the dipstick max. It should reduce this by a lot.

 

i keep my oil about 1/4 and also put on a breather tube to take excess oil to under the bike. but with the oil level lower i dont get much blow by any more

this is similar to what i did on my bike:
http://www.mklsportster.com/xloilblowbyarticle.htm

 

+3 On the oil level.

When you did yur umbrella valves did you make sure to put just 1 per rocker box and it needs to be mounted on the intake side not the exhaust.



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Rolling-on in 5th gear at high speed produces the highest load on the engine, and maximum cylinder pressures. You are getting blow-by past the rings, pressurizing the crankcase, and blowing oil out the breathers as a result. You did a compression test and got a 10-15# difference ... between cylinders or from what it's supposed to be? And how fast did the pressure leak-down?

Puking oil while on the throttle in 5th is not unusual, the Sportster's crankcase ventilation system is a poor design to begin with, and it varies from bike to bike. It sounds like you did what you could to fix it. You can try the oil level suggestions, but in my opinion that won't do much since we are dealing with a dry sump system and technically, the oil level in the bag should have no effect on what is actually in your crankcase... unless your oil pump is not scavenging properly (and then you have bigger issues)

Ultimately, you may just have to live with it... how often do you crack the throttle in 5th gear?

 

+10...i can't tell you how much bullshit i've gone through with blow by.

conversely, i think i'm on the straight now, running a breather kit to a small filter and the oil as low as i can. as long as it's showin up on the dip stick, you should be good.

 

FYI he swapped the oil pump for a Buell unit... problem solved.