can anyone tell me why the swing backfires i just got mine out of the garage and rode about 15 miles all is good then the swing starts to backfire thanks ellen

Backfiring is caused by unburned gas. If the bike is not ridden very often the gas will tend to break down and not burn as cleanly. With the addition of ethanol this is even worse. A fresh tank of gas might help. It's hard to diagnose without knowing about your riding habits and the condition of the bike. Others much smarter than I will chime in. The main thing is to let them know as much as you can about the storage of the bike, age of the bike, milage since last tune up, and any other information about the problem. I've found there are some very smart people on this forum and they will be glad to help. I hope you get it running right. Springtime is coming.

We had a few days ago a discussion about this...
I think it should be normal under some conditions but not all are confirm with me...
Do you have the backfire all the time or only under some conditions like motorbraking, after fast throttle closing, etc?

Backfire is caused by unburned fuel and there are some reasons for this. You also need air for the backfire...

Do you have the Backfire outside of your silencer or do you have the "plopp" inside the silencer? If it is inside, you also need unnormal fresh Air in the silencer, here are also some reasons and one of this is also normal...

Do you have modified anything? A tuning exhaust or a sport Air Cleaner can also cause or boost this...
What is the Maintenance status? How much km/mls are on the scooter and did you (when?) adjusted the valves?

I have found this video for example

Here you can see the (in my opinion) "normal" Backfire with an "open" exhaust (MIVV) and i would bed also a non-stock airfilter

Or here another Video with a really extreme exhaust and also backfire