my new 850 had a few loud backfires after a short ride than at idle bang!! made me jump , it did it 3 different times and the more i rode it then no more backfires. it only has 6 miles, has any buddy else have there new 850 backfire when new?? hope it just needs broke in.

 

my 09 850 did it a lot when newwhen letting off stopped doing it after 25 or so miles hasnt done it in a long time 800 on it now sometimes they say the throttle cable needs adjustment[free play]

 

Even though many of the newer machines are EFI (yours in case with 6 miles) I still feel that the break in time may will probably cure your issue. The computer is going to have to learn the A/F ratios, the way you ride etc. I know all of that is supposed to be in there but I won't accept that. Even my 2007 EFI falters a bit when the weather and temps change from the last time I rode it but it's only noticeable for the first few seconds of idle then adjusts itself. If your having this issue after 50 miles I'd take it back to the dealer to have the computer and sensors checked. Another thing that may attribute to backfiring is if your engine is cold and running rich via computer control (like having the choke set) and run it for just a short distance then shutting it down. With a cold engine you may not be getting a full burn of the fuel and leftover fuel vapor could ignite causing the back fire. One thing to note is it's not good to run your machine for short time and then shut it down. Be sure to fully warm the engine prior to shutting down. Just my 2 cents. I should also mention that the backfiring could also be attributed to a lean condition rather than a rich condition which the computer should correct with a little run time.

 

rode it some more 12 miles now and never backfired, filled the gas tank and ride it more tomorrow. the 850 engine sounds sweet compared to the 550.