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Discussion Starter · #1 ·
This probably isn't Suzuki specific, but I have a 1981 Suzuki GS550T and when it has been revving really high (it's been going for a long time and warmed up or I pumped up the rpms), then I turn it off, it pops with easily as much noise as firing a 22. It sounds like it's coming from the mufflers.

First, I'm pretty new to motorcycles and have only owned a motor vehicle for 3 years. Why would this happen?

What could cause this and how can I fix it?
 

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Backfiring like that is usually caused by unburned fuel mixture getting burned in the exhaust system.

I would pull the spark plugs and check the color and condition of the electrodes to see where the fuel mixture is sitting.
 

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Yep, after-fire like this is fairly common for Suzukis, since the idle is tuned kind of lean to meet California rules. When closing the throttle, the mixture can get lean enough that it doesn't actually burn in the cylinder, and is pumped into the exhaust, where it pops. There are many, many threads on forums asking for a solution. A partial correction is to adjust the idle fuel/air (pilot) screws, which may have been behind brass anti-tamper plugs. Every Suzi owner I know has pulled those plugs, and re-tuned the idle. There's only so much you can do, though. My Suzi still pops on occasion, as does my old CB450; I just set the best idle, and ignore the pops.
 

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Discussion Starter · #4 ·
Hey, thanks for all the info! Dodsfall - thanks for letting me know what it was called. I could finally get some relevant search results. After some research and because of what WintrSol said, it seems it may be caused, in part or in whole, by the idle screws being too high. I don't know how to change them, but the bike sometimes idles as high as 5500 rpm! I know that's not normal, so I'll try to adjust those.
 

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Discussion Starter · #6 ·
If you're referring to the statement saying I pumped up the rpm, I didn't mean right before turning it off. I meant something along the lines of just coming off a short fast ride in a low gear - so rpm was higher than average when riding.
 

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Running rich, incomplete combustion and unburnt fuel igniting in the tail pipes.
 

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Discussion Starter · #8 ·
Jay550, would that be caused by the idle screws being too high? Also, does anyone know where they are? I can't find anything about their location online?
 

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Probably on the carb. There should be 2, mixture and idle, but I'm not familiar iwth that specific bike. Mixture controls air/fuel ratio, idle controlls, well, idle. If it's an inline 4 with 4 seperate carbs, I am not sure, it's been a long time since I"ve messed with them.

Check your plugs, if they're burnt, you have to much fuel. If they're white, to much air. Check your air filter is letting air through properly if you're runnign rich. Otherwise a carb adjustment may be in order.
 

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Idling at various rpm, especially as high as 5000rpm, is an indication of an air leak. Try spraying some carb cleaner around the boots that connect the carbs to the engine; there should be no change in rpm.
 
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