I just bought a barely used RMZ-250. The guy i got it from said it had
about 5 hours on it. When I looked at it, it was obvious that he was
telling the truth you had to look hard just to find a scratch on it.
Anyhooooo he told me that the bike is still bone stock except for
Pro Taper bars, that he had them add at the dealer but i noticed
the radiator cap was a 1.8 now i have heard of putting 1.6 on
these bikes but why a 1.8. It does not have the after market mod
of the water pump cover but it is on my list of things to get.

Not sure why the bike has a 1.8, just might have been an easy size to find in a parts store. definitely not stock though. a lot of people run the 1.6 cap, but only because kawasaki stocks a 1.6 cap for the KX500 bike. either way, the coolant will be able to reach a higher pressure before overflowing. I think the benefits of this are up for debate among RMZ/KXF owners. I run the stock cap.

Yea didnt thing the cap was stock. Is a 1.1 the stock cap?

Refill with Engine Ice and get a KX500 radiator cap from a dealer and it will run 20-30 degrees cooler.