Welcome the the site !!
You mention you have had the bike quite a while , how long ?? , and what have you done to it ?? (maintenance wise/rebuilds/head gaskets, etc.)
Have you tried starting it from cold and removing the radiator cap ?? , you need to do this to see if there is air bubbles going thru the system indicating a blown/leaking head gasket or to make sure your impeller shaft in the water pump is not leaking , also look closely at the radiator cap itself , and make sure the seal is not compromised ..... running hills and sitting idling WILL make the bike overheat , why ? , because the only cooling is the air that flows thru the radiators , so when you are sitting there , its got no air flow or anything to cool the water that is flowing and it will overheat or spew out .....
Have you considered a cooling fan ?? , I made my own setup
, but Trail Tech makes a nice setup that is basically bolt on
https://www.crfsonly.com/catalog/produc ... ts_id/5360 , and switching to a 1.6 or 1.8 bar radiator cap will allow the temps to raise about 50 degrees before it starts to boil over
Also switching to Engine Ice (what I use) or Evans Waterless Coolant will help with overheating
https://www.crfsonly.com/catalog/produc ... ts_id/1920
As far as the exhaust goes , it might help if you could post a picture of it , so we can see whats going on , or if its anything to worry about .... to post a picture you need a image hosting site like
IMGUR or , if you have money , Photobucket (it used to be free to but they got greedy and lost a lot of people) or any image hosting site to use for Forums , for IMGUR you will sign up (its free) then upload your picture/s to it , then click on the picture and it will open up a little window with the picture and some links on the right , click the one that says "
BB Code (message boards & forums)" its second to last on the bottom right , it will look like this ............................................
[img]https: //i.imgur.com/yLR1FNo.jpg[/img] , then just Copy , then Paste that code in your post here
But it will show up like this when you hit Preview or Submit
Also , make sure your jetting is correct for your elevation , if the bike is stock , then most likely its lean even if you are at sea level , you need to check the main and pilot jet and see what they are , if its stock the pilot will be a 42 and that is too lean , the main will most likely be a 142 , which is too lean (this is stock jetting made to pass emissions , not run well)
This is a Jetting Guide , if its jetted to this , it should be good , and that will eliminate that as a cause or issue
Jetting Guide for Main Jet:(pilot 45) CRF450R/X
Sea level....165
2000 ft.......162
4000 ft.......160
6000 ft.......158
8000 ft.......155
Temperature/Elevation:
One main jet size (up/down) for every 2,000 feet or 25 degrees in temp.