83 XLX. Most times when I maintain freeway speed for more than several minutes, my bike will begin to backfire. What could be the cause of this?
Lack of lead additive in gas?
High speed jets problem?
Bad fuel/air mixture?
Ignition problem?
When I let off the gas and let it slow down, the backfire goes away.
Thanks for any help.

 

Additives (lead) help to prevent detonation (pinging), ....not so much backfiring.

Could be a couple things. Check you timing components and adjustment first. Kind of weird that it happens after it runs good (at speed) for a while.
Keep us informed.

 

Intake leak.

 

Your petcock screen could be stopped up, or the gas cap vent could be plugged. At higher speeds, you could be using more gas than can flow back into the carb. Next time it happens, try loosening the gas cap while still riding (not with a full tank) and see if it clears up in a few seconds. If so, the cap vent's partially stopped up. If that doesn't help, check the petcock screen. If that's not the problem, you could have some trash in the float bowl. Is the carb braced so it can't vibrate around at higher rpm's? That could be a problem, too.

 

I'm not nearly as seasoned as some of these guys, but first and foremost I'd ask if this is a new problem you're having that suddenly cropped up, something that's been going on for a while, etc.

My 83 Sporty would cough at me sometimes, when I first got it, if I kept a steady speed for any length of time. No trouble on acceleration, or maintaining speed for a short bit, but would happen more and more the longer I maintained RPM. I did some carb tuning first (my fuel accelerator pump was running WAY too rich), which helped. But ultimately I pulled out my plugs and found out the gap was off. A new set of plugs, properly gapped, has made a world of difference.

Sometimes it's just the little things =)

 

Thanks for the suggestions. I'll start with the plugs today and see if that has any effect, and then continue with checking things that were suggested. I'll get back when I figure out what was the cause.

 

What is your opinion about backfire ?
1 Popping and "coffing" in carb/airbox/aircleaner ?
2 Popping and banging in exhaust ?

 

Had one at the shop along time ago that was caused by a valve hanging in the guide, I removed .002 front the guides and the problem was solved. very hard to find that one.

 

I agree with this answer, as I had the same problem which was caused by the weight of the carb tearing the bands.

 

Like Aldamar mentioned, start out with the easiest solutions 1st which is a good set of plugs. Run the bike and try to recreate the fault. If it still spits/hiccups thru the intake look at your plug wires/coil wiring for any corrosion. Also make sure your battery connections are clean and properly tightened (assuming you have a battery). Make sure there aren't any problems that can be fixed without replacing parts.....This advice coming from one who lives on a tight budget!