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Discussion Starter #1 (Edited)
2001 Honda Shadow Spirit VT1100C 2-cylinder
I was traveling at 100kph in 3rd gear and eased the throttle and it backfired once. Have also seen where I had the wife on the back and going down hill when I eased the throttle and it backfired. In both cases it seems the engine is in high revs and I'm easing the throttle. But the bike seems to run perfectly any other time. Idols perfectly, runs well at all speeds.
I cleaned the jets just 1 month ago.

Any thoughts.
 

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Check the spark plugs to see if the fuel mixture is close to correct. I'm assuming you have aftermarket exhaust, so sometimes slight changes to the fuel mixture are required.

Is this making pops on deceleration or an actual explosion in the exhaust?

If it's running well and the plugs are not showing too rich or lean, there really isn't much to worry about unless a lot of raw fuel is getting ignited in the pipes and going boom.
 

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Discussion Starter #3
Thanks. I'll take a close look at the plugs.

It sounds like a gun shot, so I take it that it's an actual explosion in the exhaust (scares the heck out of my wife and I wouldn't want to have it happen in downtown Waco.)

As far as I know the exhaust is original. I've had the bike for 5 years and my son had it for 5 years before that.

It is rare, so I'm not worried, but it happened on the way to work this morning so it got me thinking.
 

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Discussion Starter #5
But only in this rare circumstance when the engine is trying to turn faster than the bike is going, like when I'm going downhill with extra weight on the bike, or in third gear at a higher speed and ease the throttle.
I replaced the rings recently, so it might have something to do with compression? With 1100ccs and only 2 cylinders?
I just don't know.
 

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Dodsfall has given you a suggestion and a good guestion about mufflers. Usually anytime popping happens it's because someone changed mufflers to more free flowing. That changes the air/fuel ratio. Check the plugs as suggested. I'm betting they are nearly pure white. Running to lean on fuel then. Now if it's more than just popping like a big explosion and your plugs are black then it's rich, getting to much fuel. Two completely different conditions but easily identified by simply looking at the plugs.
 

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Most of the time, some cleaning or a jet change in the carb can clear up something like that. Being stock, my bet would be on some contamination in the carb.
 

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Discussion Starter #10 (Edited)
I stripped and cleaned the carb and jets just a month ago. I didn't replace any jets, just the gasket.

It's interesting that you haven't mentioned the bike running faster than the engine condition. Is this because this is the "normal" time when backfiring occurs? If the mixture was bad, would it backfire at other times? Or is what I'm experiencing normal for backfiring?
 

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It would make sense that the engine running faster, and pulling a high amount of vacuum, would draw more fuel in if the carb allowed it. The carb working properly should shut down the flow when the throttle is closed, however.
 

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If this came on recently, then, yes, you likely have an air leak, either into the exhaust through the gasket at the head, or at the seal between the muffler and head pipe. Another possibility is the diaphragm that controls the coast valve (transient enrichment system) has started to fail, or a crack has started in the boot between the carb and head.

If it has been coming on slowly, and has gotten to the point you want it fixed, you may just need to run a good fuel system cleaner through it, to open up the passages in the fuel pathways.

If it has always done this, then the lean factory setup is the cause; sometimes shimming the coast valves or turning the idle fuel/air screws out a bit will fix it.

Just FYI, it is normal for CV carbs to create a lean mixture as the throttle is closed; just the nature of that type carb. Leaning out on decel will cause the mixture to ignite poorly, dumping unburnt fuel into the exhaust, where it then can explode. That's why they added the coast valve system to most of them, especially on large engines.
 

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You can check for a vacuum leak easily by spraying carb cleaner around any suspect areas while the engine is idling. A change in RPM signals a leak.
 

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The 43rd Poser
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If the exhaust is stock, thus not changing the AFR, I would look for exhaust leaks.

Quite often the culprit of decel pop.

Start the bike, and with a lit cigarette or cigar, run the length of the exhaust system, watch the smoke for clues of a leak.
 
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