The stock Kawasaki KFX450R fuel tank is a pathetic 2.6 gallons. Not
bad if you are just riding around the track, but for long rides in the
dunes, it just doesn't cut it. For example, up in Idaho at the St. Anthony
Sand Dunes, we started from Sand Hills Resort heading for the big dunes past
Egin Lake. I didn't even make it to Choke Cherry before I had to turn
around.
I also like to make the 40+ mile run from Gordons Well up to Glamis and
back, and I knew there wasn't anyway the stock KFX450R fuel tank would make
it.

OEM Kawasaki KFX450R Fuel Tank - 2.6 gallon
Thankfully IMS Products makes a 3.7 gallon oversize tank for the KFX450R.

IMS Products makes a 3.7 gallon oversize tank