07 honda 250 trxte,idles fast every time i remove gas cap then put it back on,?

[hoot]

hello folks,i have a 07 honda 250 trxte 250 atv if i take gas cap off to check the gas it idles fast when it gets hot,i can leave it sit over night and it idles fine until i remove the cap again,i checked the vent line and cap i can blow through it or suck on it and get air,i put in new spark plug and drained the gas tank and refilled it with fresh gas it had some drugs in the carb that came out when i drained the tank,thank you for any help, hoot