My rubicon isnt running right i was using it earlier today and all of a sudden it died which it has been doin recently but when i went to turn it on i pulled the choke and it started and as soon as i let go of the choke it dies and wont stay running my friend told me to  change the spark plug so i bought a new one search arouond for where the sparkplug was and found it i tried taking the cap off but couldnt ( didnt want to pull to hard) then i opened the box with the new spark plug and noticed the top of the plug had threads on it to ive never seen this before ( my first quad usually work on sleds occasionally) somepone please help me with this im not sure if its the plug that is bad on my quad thats y it keeps dying any suggestions please