Hello everyone!! A friend of mine has a sportster that had been sitting up for a while and wouldn’t start. Went to take a look and the plugs weren’t firing – changed them out and it started like a champ. Let it run for about 20 minutes and it sounded great so I decided to take it for a spin, but after cruising for about 10 minutes it started to backfire and eventually crapped out and wouldn’t start. Let it sit for about 30 minutes and then it fired back up. It was still backfiring, but after idling for a while it eventually stopped so I took it for a spin again. Same thing – ran great through the whole range of rpms, but after about 10 minutes it started to backfire and crapped out again. This happened one more time. Anyone have any ideas? Strange thing is it runs really well for a while, but once it warms up it starts to backfire and then dies. Thanks in advance.