My 86 R80RT recently return from a 1000 mile trip. Ran Great. Had the Carbs balanced two weeks prior, values adjusted 3000 miles ago, and it has always started immediately, (fast) and with no problem. The other day, I took it for a short trip. Drove about 150 miles and went to a gas station. Filled up and when I went to start it, it took about 3 seconds to turned over and when it did, it had a slight "spit" backfire> Never did that before. The rest of the day - no problems. This morning I pulled it out of the garage, turn the petcocks on, flipped the enricher over, and when I hit the starter, it took about 4 to 5 seconds to crank over and when it kicked on, it backfire blowing small flakes of carbon out of the exhaust. After that, no problems the rest of the day. What is my bike trying to tell me?

Thanks