new back fire/ popping on deceleration??

91 1100 with 136,000. stock exhaust, K&N air filter
well maintained by yours truly. Recently on deceleration I get a popping . Used to be smooth no noise. Air leak?? Where to Look first?

knobs said:

Used to be smooth no noise. Air leak?? Where to Look first?

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I would suggest the vacuum tubes which are capped off to provide the vacuum take-off for carb adjustment. The ends should be just visible at the top side of each of the cylinders above the plastics cover lids. They are connected way down into the V - needs a light and mirror to see and long, long nosed pliers to push them back on.

Afterburn.

Exhaust manifold/muffler pipe leak/hole.
Air cut-off valves.*
Secondary Air Supply System fault.* (Easy to check!)
Hoses of emission control system fault.*

* p5-2 Honda Service Manual, Troubleshooting

Edit: if the engine runs smooth I’d think the intake side (intake manifold ports or carb boots) isn’t involved... Air is getting into the exhaust side. Some decel burbling is normal but the OP is reporting a change/something new.

John

Has the air filter been added recently? And when was the carb set, last balanced?

John OoSTerhuis said:

Edit: if the engine runs smooth I'd think the intake side (intake manifold ports or carb boots) isn't involved... Air is getting into the exhaust side. Some decel burbling is normal but the OP is reporting a change/something new.

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I bow to John O's superior knowledge on this. My comment about the vacuum tubes was from personal experience when it turned out that one such tube had been disturbed at some point, and came off mid ride. Lots of popping and back firing - but reading my notes at the time, there was also a very obvious loss in power. (0-60mph in about 3 mins ! I exaggerate of course, but not by much).

My hunch is a hole in the muffler or exhaust pipe somewhere.

I'll go out on a limb.... side stand switch starting to go, red wire coming loose at the main relay, that can cause backfire, or popping on deceleration.