Not sure what's wrong with this thing at this point. Occasional backfire while starting it, and it still only wants to idle with the choke on. I was able to ride it and once I got going it would run with the choke off but I had to keep the rpm's up or it would stall. pops quite a bit when coming off throttle while it's in gear. I blew out all the passages with compressed air and a full can of carb cleaner plus I replaced the jets. The choke button does not like to stay out now so I have to hold it with my hand while I start it. Are my valves screwed? This is the first 4 stroke bike I've owned and so far I really don't like it. The bike is in good shape but I can't figure out why it won't run right. It's a 2005 YZ 450F. I drained the tank when I had it off so it has fresh 93 octane gas in it now. Anything else it could be besides the valves? Thanks.