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My best friend has an '01 blue S. For the last week shes been popin real bad. Both at an idle and goin down the road. While accelerating the bike runs fine. When motor braking she sounds horrid. I'm lost. I own a second gen and don't know as much about his bike. We've checked plugs, valves, air filter, exhaust, and all seem to be OK. Ran a tank of high octane w/ no additives and no improvement, actually think it's getting worse. Are we missing something that we can do ourselves(both being mechanically inclined). Any and all help appreciated.

Bike
01 SVS
KN air filter
Two brothers exhaust
dynojet kit
Thats it except a bunch of powdercoating and carbon fiber

Thanks in andvance for any help.
 

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First guess: sticky and/or leaky needle and float in one of the carbs (rich).
Second guess: vacuum leak in the boots between the carbs and the heads (lean).
Third guess: plugged (dirt or water) fuel circuits leading to lean condition (lean).

Rich or lean conditions can cause backfire. In the case of rich conditions either misfire or incomplete combustion puts raw charge into the exhaust pipe. Next exhaust event ignites the mixture and causes backfire. Lean condition is the same, but misfire is what puts the raw charge in the tailpipe.

In my experience lean conditions are the more common cause of backfire.

So check for water in the fuel bowls and look for vacuum leak first. If you find nothing then consider disassembly of the carbs. Premium fuel will do nothing that regular fuel won't do. It's all advertising B.S. Some of the fuel system additives work pretty well, but they're risky unless you are sure they are safe for the various gaskets and O-rings in the fuel system.
 

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The easiest way is with starting spray. You can buy cans of starting liquids in spray cans. Start the bike and shoot quick, light shots around the rubber connectors. If there's a vacuum leak the engine will momentarily speed up. Don't spray too much, just enough to get the vapors around the connectors.
 

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Andy, how would one check for water in the float bowls w/o disassembling the carbs? This may be a dumb question, since I haven't taken the carbs apart on the SV yet, but the other carbs I've taken apart required removal before being able to get at the float bowls.
 
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