Have you pulled the carburetors, cleaned them, and checked the jetting? 50 miles per tank is pretty bad, for trail riding at least. Even riding in the mountains, my 600 still has at least a quarter tank after fifty miles. Could be bad jetting or a choke hung up or out of adjustment. With regard to oil, the first thing to check is if the oil pump alignment mark is lined up. It should be easy to see if the carbs are off, but you may need an inspection mirror or camera to see it otherwise. There's a line on the arm of the pump that moves with the throttle that should line up with a mark on the body of the pump at idle. That may be out of adjustment, but even with it lined up, you'll still want to monitor oil use. Best way to do that is to run the oil tank down as far as you feel comfortable, then incrementally add a measured amount (I'd recommend a pint), making a mark at the oil level each time. Then, when you fill it, you can get a good idea where you're at (40:1 would be two pints to 10 gallons of oil). Keep in mind, if the carbs are throwing too much fuel in, that'll cause a "lean" oil ratio, so don't worry about fine-tuning that until you've got the carbs squared away.
