just bought this 400 xplorer all it does is click when i tried to start (battery is good) so itried to pull start started up 3rd try drove it maybe 1/2 mile started losing power and died now wont start it backfired once pulled spark plug and it was dry found a hose that was off that carried coolant to motor put back on now when i try to pull start coolant resivour bubbles (was dry had to fill) did i blow it up or how do i fix

 

Here's your best beet, drop some oil down the spark plug hole, pull it over about a dozen times, next if you have a pressure tester, check compression. Advise

 

sounds like its time for a rebuild, i bet the previous owner was aware of the problem and unhooked/drained the cooling system to prevent it from showing those symtoms while he was selling it but... you should have first b4 ever ripping down the road on a new used quad for the first time :
check all the fluids.(antifreeze, counterbalancer oil, tranny fluid,brake fluid, injector oil, gas etc...)
inspect plug
check air filter
inspect chain and sprockets
start it and check for leaks or strange noises
top off the oil tank (to make sure the injector is working)
then go for a test ride

 

usually if it has air bubbles in the antifreeze it might be a blown head gasket. cant imagin that it had too much antifeeze in it if the rad. hose was unhooked?