Help I have a dr 250s that is putting oil back through the drain line at the bottom of the air box ant one know why

May not be the carb at all. You have somehow managed to suck gas into the oil. Take the plug out and crank it a few times. It will likely throw excess gas and oil out of the cylinders. I had the same problem with a brand new (5 hrs.) DR Field and Brush Mower that was equipped with a "carbon recapture unit" - a ridiculous new EPA requirement. Rather than a simple vent on the gas cap, these geniuses have put a valve at the top of the gas tank with a hose running back into the carb. No problem until you fill the gas tank and try to mow uphill more than at 25 degree angle. Then, what happens is when the gas level in the tank makes contact with the valve, you wind up with an air filter full of gas and gas/oil in the cylinder. You'll need to replace and gap the plug, drain and replace the oil, install the CRU (if it has one) replace the air filter, and it should be ok. I'm going to bypass this CRU. The EPA, for all the good work they do, gags on a gnat but swallows a camel. Good luck. P.S. My DR is still in the shop.

Put car on ramps. On the lowest point of bottom of the motor, you will see a bolt. . Place drain pan under the bolt, and turn bolt all the way out. Drain all the oil out and re measure what you're putting back in. Place 3 and one half liters back in as the filter holds almost a half a liter. Try not to run the car as you may hurt valve seals air filters etc.Good luck let me know how you make out. Please rate this solution Cheers from Nova Scotia!!

Not a big deal. Im assuming this is a 4-stroke push mower and not a leaf blower.
Remove the air box cover, air filter, and air box back plate. Careful there is a gasket on the back of the backplate that if damaged the primer bulb wont work, part # 272653. Remove the fuel line from the carb and drain the tank. Using a 1/2 inch wrench remove the bowl nut from the float bowl on the carb, hold the bowl to the carb as to not break the gasket seal, drain the bowl and replace the bowl nut. If you tried to run the unit and oil is in the cylinder remove the spark plug ( clean the spark plug) and spray some carb cleaner in the hole and pull the starter rope several times to purge the cylinder. Reinstall the spark plug, reattatch the fuel line, install the air box back plate ( leave the air filter and cover off for now), add fresh fuel.
Take unit outside and start, you may need to give it a shot of carb cleaner in the throat of the carb to help it start. It may smoke, it may blow oil out the muffler. Let it run until it quits smoking ( usually around 5 minutes) . Shut it off and complete assembly. It should be fine.

Take off the side covers , unbolt the seat and remove( two bolts), the air box is under the seat. Flip the two tabs and lift the cover. Unscrew the center wing nut and lift the air filter out. Clean it, re oil it, and put back in, reverse order.

there is a drain bolt on the bottom of the motor.. take it out let all the oil come out and then fill back to the recommended amount or if it has a dip stick fill to the full line

Often times there is a engine breather tube that has to do with emissions that runs from the engine to the air filter breather box. This tube can in some cases blow oil through it when the engine is run hard. Make sure you're not over filling the engine with oil when you change it because this will cause the oil to "blow off" the excess and the air box is where it often goes.
There is also another possibility, are you using too much oil in your air filter after you clean it? This too is a common cause for oil in the air box, if that's the case I would not worry about it.
The last case scenario is one you don't want, that would be washed out rings which cause blow by and that in turn causes the engine to blow oil out of the breather tube which I'm confident it venting into the air box.
Please let me know if these resolve your question and if not give me more details and I will be happy to assist you further.
Regards,
RSelvy