I recently acquired a couple of ATV's (4 Wheelers). After having them for a few months, I finally got around to getting them running. On the 1st bike below, I did brake work, battery & Carb issues. Nothing related to oil.

2002 Honda Foreman 500
I got this running about 3 weeks ago. I've been running them around the 5 acres here during the 3 weeks or so before taking them out to the farm 50 miles away for some bigger adventures.
When I worked on them 3 weeks ago, I made sure to check the oil levels etc. Oil was seriously low. Added oil. Ran around the five acres here for 15 minute intervals give or take.
Wife & I made that trip yesterday & rode for about an hour or so. I checked oil levels before leaving home. Sure enough, its way low. Filled with oil. After the ride & got home, checked & seriously low again.

I let these bikes run at idle or 15 minute intervals upon checking them out & completing the work. No oil leaks. I have let these bikes idle every time I have used them just to check tout their conditions, since I don't know much about their mechanical history. Again, no oil leaks at idle & I don't see any oil on the engine.
So, that leads us to consumption. It does not smoke even one iota. None.. period. Not on start up, not on hard acceleration, not at idle for periods of time.
Yet, I'm missing a quart plus in a one hour use.
Only reasonable explanation I can come up with is loss during use/riding, but again, I don't see any oil leaks on the engine. I'm not 100% on that fact, but in general looking, I see no oil leaks on the engine.

@cheeze

 

I would look at the crank case breather. It probably is routed into the intake to burn the oil smoke. If you've got worn pistons/rings or a blown head gasket you could be blowing a lot out the crank case breather. I have no idea why you aren't seeing any smoke though.

 

Mr PD, there is no oil in the breather....

 

does it have an oil cooler that could possibly be leaking or lines going to it?
what does the spark plug look like oil deposits on it?

 

It does not have an oil cooler. I haven't pulled the spark plug since there's no smoking. I haven't considered that but I can. i'll do that this weekend if I get a chance & report back.

 

If it is not going on the ground then it is going out the tailpipe. Check the spark plug. I don't know how much oil has to burn until you see blue smoke but I would be betting it is more than you think.

 

Way back when I had a chevy with one broke ring. 2k miles around town and it wouldn't use over a half qt of oil but 200 miles down the interstate and I had to add a quart. Never saw any blue smoke out the tailpipe.