Anthony, everything you're reporting on your used KLX smells of, at least, a carb rejet perhaps even MCM.. Can you contact the previous owner (PO)..?
I can imagine a stage 1 carb with MCM and 15 tooth primary sprocket going 88 mph with stock exhaust and airbox..

 

I bought this straight from the factory (Lake Forest, CA) through an employee buy program. IT had 400 miles on it but no reported mods, nor can I see any that were done. As for rejetting, the air/fuel screw is still capped.

I'm not too concerned any longer, just gonna run it!

 

Your not alone! mine does as well, full choke fires right up, let it on choke for a bit to warm up and your ready to roll!! Factory Stock Carb I want to mess with the carb but am afraid of messing it up.

 

2014 klx 250s bone stock with 5500 miles runs 97mph indicated. Stupid scary though.
Fires right up every morning, even after sitting for a week or 2. Perfectly reliable, I bought it used with about 500 miles a couple of years ago. Mostly running Shell gasoline through it & altitude is only 137' if that matters.

 

I see you revved an old post. I'll chime in with an update. Mine also still starts right up, warms fast and is still on the original 2014 battery. I now have over 3k on my bike, changed the sprockets, now running 14/50 for a bit more pop, and still manages freeway speeds acceptably. You stated "scary", my advice is move your butt far back on the seat at freeway speeds, makes a great difference. Happy, happy, happy.