What is the proper crankcase oil level for a Briggs and Stratton 5.0 horsepower 4 cycle. I bought used one that didn't have a user manual. I filled crankcase to bottom of threaded fill plug and when running oil ran out of air filter. Any information will help

There is usually a slot like thing in the oil fill port. Fill to the top of the slot, just like you would put water in a car battery.

I doubt you overfilled it.

The oil breather needs to be replaced. Find the engine model, stamped on the blower housing and go to Home - Briggs & Stratton (http://www.briggsandstratton.com) and/or Parts & Accessories | Shop & Find Lawn & Garden, Appliance Parts at Sears Parts Direct | SearsPartsDirect.com from Sears (http://www.searspartsdirect.com) Both should have parts. The tear down manual will be better at B&S. Find the oil breather in either location.

If the tiller has a model the sears site should cross referance.

There is usually a slot like thing in the oil fill port. Fill to the top of the slot, just like you would put water in a car battery.

I doubt you overfilled it.

The oil breather needs to be replaced. Find the engine model, stamped on the blower housing and go to Home - Briggs & Stratton (http://www.briggsandstratton.com) and/or Parts & Accessories | Shop & Find Lawn & Garden, Appliance Parts at Sears Parts Direct | SearsPartsDirect.com from Sears (http://www.searspartsdirect.com) Both should have parts. The tear down manual will be better at B&S. Find the oil breather in either location.

If the tiller has a model the sears site should cross referance.
It does not have an oil breather. It has a dry air filter.

Oil breather's look like:
http://thumbs.ebaystatic.com/pict/1400019856304040_2.jpg

It's an open small hose pointing down usually on the side of the engine with a filter internally attached. You really have to look for it.

All small engines have them. When they are plugged you pull oil into the air cleaner.

Your talking about an oiled foam air cleaner.

I'd bet you money that it has an oil breather, but it's against the rules.

Look up your engine and/or tiller model and do some leg work. I can't without that information.

We used to have oil breathers on car engines, but that's been replaced with the PCV system. The oil fill cap was vented through a filter element.

Yes it does have an oil breather to ventilate the crankcase. It is a small rectangle shaped box about 1 1/2" x 2 1/2" and has usually a black tube coming out of it to the air filter housing. I fill the engines to the top of the threads on the lower fill port.