650L Diagnosing Misfire/backfire

Riding a 2013 650L XR'S ONLY headers and exhaust. Daves mods 55/160 jets sea level. Adjusted my mixture screw somewhere near 2 and a half turns out... but the $70 motion pro carb tool i bought to adjust the mixture on this bullshit 2013 carbs, decided to literally fall apart in my hands the first time i used it. I took it out for a spin and after a while of riding i would blip the throttle and the exhaust would cough and the bike would shit out on me. It started right back up but happened a few times. I somehow got the tool back together to turn the screw in a bit. The bike runs a hell of a lot better with the adjustment but when decelerating from high RPM's i get an intermittent backfire from the exhaust. It's not your normal popping on decel it's a loud ass bang that sounds like a shotgun going off. It only happens when decelerating from high RPMs with the throttle closed. And seems to happen more before the bike gets warmed up. Could this cause any problems? Is the bike running wayyy too rich now? I haven't checked the plug color yet. I'm not very privy to how engines work and the more mechanical side of things so maybe me running rich and stickin 89octane in the bike causing unburnt fuel to detonate? I'm at a loss. I'm more worried about the backfiring causing any internal engine problems because when it backfires it sounds pretty violent. If someone could fill me in on some knowledge or a resolution i'd appreciate it.

mmm..a screwdriver is normally all you need to adjust the mixture/air screw..I duuno what's up but as you say huge shotgun type explosions are normally caused by unburnt fuel igniting..You can cause them yourself by hitting the killswitch when running at a good pace or downhill and giving the engine a lot of throttle/gas intake then turning the killswitch back to run (boom)..don't do it around horses..


I suppose the timing may be slightly off..have you checked the tappet/rocker gaps,??,you don't want them overly tight,,causes hard starting and bad detonation type stuff..ie,,bad kickback..Course you wouldn't notice that as you have no kickstart..I class kickback the same as large shotgun type explosions..Timings out thus things explode at the wrong time..thus kicker breaking your leg or in your case,,the massive bang when the bikes decelerating..

Edited by Horri

Check your valve adjustment.......



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