Venting trans oil

I've been working on getting my 'new to me' '83 CR500 ready for a little vintage. I have some jetting challenges to work out, but my question to you guys is regarding trans oil coming out the vent hose. The fluid level is correct, but every time I take it for a quick spin, I get a little puddle on the floor from the vent hose. Could I have a leaking crank seal? It starts easy and runs pretty well, no excessive smoke. I'm not familiar with reed valve engines but I'm wondering if it could be blowing crankcase pressure past the left seal.

There's an old back-yard mechanic test for early air-cooled Husky's to see if the clutch-side crank seal (which is installed on the crank side of the main bearing thus requiring splitting the cases to replace) is leaking.
Route the trans vent tube to a bowl of water. Start the bike. If the vent blows bubbles...the seal is leaking case pressure.
Not sure if that applies to an 83...I consider them modern bikes!
But you may want to give it a try.
Sure sounds like a leaking seal...

Thanks for the information. I'm used to a leaking seal on that side drawing in oil and causing a lot of smoke rather than loosing crank pressure from the crankcase. This is the only bike I've ever owned with a reed setup and I'm guessing that changes things in this area.

how much fluid is in the case? sounds like its overfull..often this will happen if too thick of oil or overfilling happens. try 1.5 qts of atf and see what happens. the water bowl test would work here too im thinking.
i used to have this problem running belray gearsaver in the winter..after switching oil, its never happened again..

ive had some overflow at times using atf. I put a slightly longer hose up the main down tube and problem solved. one thing I can tell you is when a lc bike waterpump fails...lots of stuff comes out that breather

I don't know if this is germane but when I bought my '82 250WR as a leftover in '84 I was told to warm the bike on the side stand buy ( not sitting on the bike of course ) turning the idle up a little bit and watch the tranny oil rise up in the clear tubing. When it got close to going in the air box I was told to shut it off and wait until it the oil all went back in the case. If that was done then I was good for the rest of the day.

the oil should never rise up the vent line.

u know the correct level is not up to the filler plug ? its like half way .only some bikes have it marked

my bike 82 500 just has the tube to the stock location on top of the air box and its never had oil up it

I replaced clutch plates and springs then filled it with measured 1.6L (what my book says) of Maxima 80 wt. Sounds like that may be a little too much and a little too heavy based on some recommendations here. I haven't really gotten it totally warmed up yet either. I think I'll just keep working on my carb settings and see how things go with the oil in the vent until then. Thanks again to everybody who offered advice.

Had a bit of trouble with the gear oil foaming and spilling out from the vent tube on my 82...... Switched to ATF (type F) , problem solved.

80 wt??? atf is 7.5, and the recommended oil is 30 wt.

30 is fine of course....manual actually states 20w for primary kick 2 strokes.
type f is 20w, thats why its recommended over other atf types. most atf fluids are around 7-10w.

gear oil is way heavy, and likely why its foaming. i had the same problem way back in the day running gearsaver.

Keep in mind that 80W gear oil is the same viscosity as 20W motor oil. Additives (especially when it comes to wet clutches) is another discussion.

Attached are links to Oil Viscosity Charts:

https://bobistheoilguy.com/viscosity-charts/

http://www.acculube.com/lubricant-viscosity.html

I make sure the vent hose runs up the frame near the carb boot on the air box then a short U turn facing down. On the newer cases '82 up I fill the oil lever to the bottom of the filler hole with the bike standing vertical. That's the bottom taper flange on the filler cap hole. Using ATF oil is ok. Or motorcycle 2T tranny oil. Remember new modern engine oil has had the lube for wet clutch plates removed. You will burn up the clutches. Use the proper tranny oil.