I've been flying my Rambler with a Saito 72 for about 6 months now and it is well broken in with probably over four gallons through it. I have a fuel line connected to the crankcase vent and I've noticed, (since new) that it is always very dry and very clean indicating that little to no fuel is exiting. The engine runs perfectly so I'm not worried about but, how much residue should be leaving the crankcase?

If you are running, sort of, on the lean side and running all synthetic lubricant, you probably wouldn't see much.

Quite a bit actually. Saito has moved the vent connection to the front of the engine. I suspect they did this to provide a more positive flow of oil to the bearings ,and more importantly the cams and cam gear. There were a few bearing , lifter and cam gear failure that may have been headed off by this wise move.
If I had any of the older Saitos I would consider updating them to the newer arrangement. Jusy my experience Based on a few bad bearings and 1 very bad cam gear, As well as a few other engines that crossed our bench.

Quite a bit, & not so much are very generic terms, and does not really answer the question. To me a tablespoon full in a gallon of fuel would be not so much , but a cup full in a gallon of fuel would be quite a bit, so what is the amount in a gallon of fuel that goes through the vent. Not trying to bust chops or be picky, just would like a measurable amount please. Thanks.

It's been my experience that the oil comes out of the crankcase breather in a very fine mist, almost invisible. If you put your finger near it, your finger will get wet with oil. Also it will burn ya.

Just to add to things, the vent is not only an outlet it is also an inlet, when the piston goes up it pulls air into the crankcase as well, its not a one way vent. some of the oil is pushed up the cam and pushrod tubes , probiibly 2/3rds of the oils stays in the combustion chamber and exits out the exhaust, the crank and bearings are only lubed by blow by oil from the combustion chamber and threw the valve guides. The oil out the vent is only about 1/3 rd of the oil in a tank of fuel , 10oz tank / 2 oz of oil for 20%oil, around 1/2 oz will probibly come out the vent if that much and most in a vaper. IMO sence this is a small amount that actually gets to the crankcase is why I like a litle Caster in my fuel.

I've noticed, here on RCU, that Saitos generally have a lot of blowby coming out the crank vent. Maybe you have an engine with a VERY good ring seating. The amount of oil in your fuel will also have an effect on the amount of blowby. Four-Stroke fuels often have less oil in them (~16%) which won't produce as much smoke or vent expulsion. The advantage I would imagine would be less carbon build-up inside the head and on the muffler, plus a higher percentage of burnable fuel in the mixture.
Personally, I'd try running it a little richer to see if it makes a difference in the blowby. I'd use afterrun oil too. Try placing a plunger on the vent working it in and out to see if there may be some blockage. A piece of crud or machining burr may be hindering the effectiveness of the vent.
Just some thoughts.

Jeff

I've been running Synthetic oil fuel. 18%oil-I think and 15% nitro. I keep it on the rich side around 400-500 rpms from max. I get a nice smoke stream exiting the exhaust. I'll try to put something in front of the breather to see if anything comes out. I was lead to believe it would spew out of there in bursts.

Don't expect to have oil residue spewing out of a healthy Saito. As previously posted, some will have a light, clear film and others may have a darker or heavier outflow. Unless it's a visible and continuous flow, you're OK. A 300 RPM drop from max speed setting is just fine and you are describing a very healthy motor. - Feed it some Wildcat 15% fuel or even some Hobbytown USA 2-4 stroke fuel (Wildcat in a house label) and go enjoy it...

quint

Cool, Thank you all for your very helpful posts!