Just changed oil and trans fluid. Now the thing has to have the choke on all the time to run. If you take the choke off while warm it will run when you throttle but at idle it stops an will not start unless choke on. Will go WOT but I can hear popping or backfire from rear especially on slow down. Did not do this before oil change. I also installed an inline filter. Could this be the problem> 1996 sportsman 500 carb 600+ miles only. Ideas? thanks