2005 C-50 Suzuki Boulevard - A back fire occurs with the throttle open. Stock pipes never changed. One very loud backfire at about 30 mph winding/slowing down. No tach on board. Bike has only 4k miles and pipes look clean and hole free so far. Garage kept.

check for problem coil/s and ignition control module
the indications that an electronic component is failing when it gets hot and causing intermittent spark

Preventing Backfire on Motorcycle Exhausts ' DoItYourself ...

www.doityourself.com/.../5-tips-to-preventing-backfire-on-motorcycle-e...

When the engine on your motorcycle has an emission system malfunction, such as anexhaust leak or a moment of running rich or running lean, backfire can ...

Exhaust backfire, popping when letting off throttle - Motorcycle Forum

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Apr 26, 2009 - 28 posts - ‎17 authors
Exhaust backfire, popping when letting off throttle General Motorcycle Discussion. ...You can damage the engine by running too lean or rich. Backfires on deceleration
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Jun 12, 2010 - A visible flame may momentarily shoot out of the exhaust pipe. ...Another backfire situation occurs when the engine is running rich, meaning ...

Is backfire when decelerating a bad thing? : motorcycles

timing off
valves too tight
too lean
TPS bad
chipped valve, bad valve seat, cracked exhaust pipe sucking air in and igniting.
any # of things can cause backfire.

BE VERY SPECIFIC AND AS DETAILED AS YOU CAN ABOUT WHEN AND HOW THE BACKFIRING IS TAKING PLACE!

when is it backfiring? accel? decel? constant throttle position?
is there ever a point when it is not backfiring?

After-market exhaust system or stock?

A lot of after-market mufflers don't cover up a backfire pop on over-run in the way that the stock system does. Look at The Marble Mod on GIXXER forums for ways to doctor the bike's emissions system to stop the popping.

Another cause of an over-run backfire may be a slight leak where the header pipes emerge from the cylinder head. Check the bolts are tight. Consider new copper washers.

There is no adjustment on the fuel injection model unless you put it on a computer and have it remapped.

When you put straight pipes on the bike, you did away with a baffle that was in your stock pipes.
so now there is no back pressure, and your bike is breathing now.
But it can't breath if it can't get the air.
When you remove the air cleaner it breaths.
So you need to purchase a High-Flow air filter.
If you have an airbox, you may need to eliminate that as well, but start with just the high flow fliter first.
When putting on straight pipes and a high flow air filter , you will also need to increase your carburetor main jet size at least 1-2 numbers:example:stock 120 go to 122.
if you don't increase the main jet your bike will run lean and hot.

Once done you'll be able to crack that throttle and the whole neigborhood will here ya.
Loud pipes save lives.
Best Regards
Big Al

maybe vacuum leak?

These will backfire when you let off the throttle if the idle is set low. When set low enough to sound "right" you will get the backfire. Set the idle up a bit and you will lose the backfire but it will sound like it is idling a bit fast.

Check valve adjustment and cam chain tension

Backfiring when the throttle is closed shows a lean mixture. Either you, or your mechanic should take a look at the mixture, and there's a 99% chance that that was the cause of your problem :)

backfiring means you have an air leak or a lean mixture. Look for leaks at the header pipes or perhaps a crack in the exhaust.
Cold air getting into the exhaust is usually what causes the backfire noise.
You may have a lean engine running situation but the bike would have other issues besides the backfire.
Let me know if you are having any other issues or if it just the backfire.
Regards,
RSelvy