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Discussion Starter · #1 ·
My mother has a 2006 suzuki s40. It is a single-cylinder 650 i think. Any ways, since day one, we bought it with half a mile on it and now has 4500 it has always back fired during deceleration. It doesnt do it all the time but something like this. If she gets up to 60 and lets the throttle off 5 times a day, it may backfire 2 or 3 times a day. Her friend has the exact same bike, same thing, bought it new with a mile on it. They both have taken it to the dealership and they say that it is normal for that bike. Something about because it is a one cylinder something something something. I personally dont not think that it is normal. First idea is to check valve clearance, When I did it the first time, everything was normal, Its bee 2,000 miles now and I will be checking again but everything at this point has checked out fine. I have checked the bike over and over again and cant think of anything else that would cause it other than valves. I am starting to believe that this is truely normal for that bike. Before I start letting it go, I want another opinion on it. Does anyone else have a s40 and share this issue? If it is not normal, what can be done to fix it?
 

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The mechanics are right, it is normal. Why? Because to meet EPA emissions, every bike runs lean. Add more fuel to the carbs, either by screwing out the fuel side of the carb, or by screwing in the air side of the carb, allowing less air into to it to richen it up.

If this doesn't work, go 1 size up on the main jets.
 

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Backfire in a motorcycle engine typically results from various malfunctions related to the air to fuel ratio. Usually, backfiring occurs in carbureted engines that are running lean where the air fuel mixture has insufficient fuel. ("Running lean" is typically a sign of mal-adjusted carburetors or fuel injection where there is not enough fuel for the amount of air). Afterfire occurs in engines that have an emission system malfunction (air injection system diverter valve), exhaust leak or unburnt fuel in an exhaust system in which the catalytic converter has been removed. When a driver shifts up and lets off the accelerator, the engine has a moment of running rich or with insufficient oxygen. This causes an incomplete burn which causes the fumes to explode in the exhaust system. The leak itself is the most dangerous aspect. Without it, the mixture would cool enough not to explode. A fuel injected engine may backfire if an intake leak is present (causing the engine to run lean), or a fuel injection component such as an air-flow sensor is defective.
 

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Discussion Starter · #4 ·
Thats a good bit of info. Thanks. I dont feel confortable messing with carbs so I wont touch it and just let it go. At least I know theres nothing really wrong with it. Thanks much for the info.
 

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If it really bothers her, find a decent mechanic. You don't have to disassemble the carbs, just turn a screw where necessary. They shouldn't charge very much, either.
 

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My mother has a 2006 suzuki s40. It is a single-cylinder 650 i think. Any ways, since day one, we bought it with half a mile on it and now has 4500 it has always back fired during deceleration. It doesnt do it all the time but something like this. If she gets up to 60 and lets the throttle off 5 times a day, it may backfire 2 or 3 times a day. Her friend has the exact same bike, same thing, bought it new with a mile on it. They both have taken it to the dealership and they say that it is normal for that bike. Something about because it is a one cylinder something something something. I personally dont not think that it is normal. First idea is to check valve clearance, When I did it the first time, everything was normal, Its bee 2,000 miles now and I will be checking again but everything at this point has checked out fine. I have checked the bike over and over again and cant think of anything else that would cause it other than valves. I am starting to believe that this is truely normal for that bike. Before I start letting it go, I want another opinion on it. Does anyone else have a s40 and share this issue? If it is not normal, what can be done to fix it?
turn your air/fuel screw to the left just a tad. it will show you where that is in your manual. it is easy to do if you know which screw, be careful though if you adjust the idle screw (which will be near it) it can have bad/good effects. bad becuase youll idle is much higher and youll eat through gas considerably faster. good becuase you wont stall when you use the clutch as easy as you would before. goodluck!
 

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Discussion Starter · #7 ·
Alright, sounds easy enough. Just a tad? Got it. Ill try it and see what happens. If it screw something up, Ron Ayers motorsports is right up the road. Thanks
 

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Just a thought here. If you adjust anything remember where it was. Then if the problem worsens put it back where it was.
 

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suzukisavage.com shave white spacer on the needle turn a/f screw to 2 1/2 turns out
 
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