supposedly suzuki has been using a certain size needle jet, and also putting a plastic washer there for emission control purposes...plus being a single cylinder backfire is inevitable....however once its broken in it should cut back some...most of the backfire is on downshift...example your cruising and you shift to fourth or third and let off the gas to coast..it will backfire...fuel builds in the exhaust and just ignites....the post with the dynojet adjustable jet is probably a good thing if you can find someone to install it....the holes in the pipes however...the owner was probably listening to friends and may havebeen trying to make it a little louder....

 

They ALL backfire. THe problem I am having is with the cheap Rectifier they put on the bike. I have an 06 and have been through 1 reg/rect. replacement and 4 batteries at this point. I should have bought a bigger bike. Or at least one with an alternator

 

The cure for s-40 or ls650 savages backfiring on decel. is not to change needle or plastic ring or jet kit, The carb has whats called an anti backfire valve, also called decel valve,or cut valve,it is located on side of carb with 3 screws (rectangular pattern) the problem is the spring in the diaghram is to stiff, remove diaghram and cut one full round off spring this will allow diaghram to open sooner on decel and allow more fuel to motor stopping backfire problems.

 

Well on the S50 I put cobra slip ons that sounds great on the bike without rejetting the crabs, but yes it does pop sometimes when I shift gears, but not everytime. The only way I know that will help stop the poping would be having your pipes tuned and carbs rejetted. Pretty much this should help solve your problem. On the other hand.... I have friends who like to hear my pop and believe it or not, they are trying to set there bike the same way. Go figure, I can't explain why. Hahahaha

Ken

 

Has there been a fix for the S40 backfire?

 

Bought an 07 S40 which backfires every time its shutoff...#1 fix on this bike for such a problem is to install 13481-24B00 spring under the carb cover with 3 screws found on the right side of bike,something about tension difference.

 

The solution is very simple, and I am constantly amazed that most of the mechanics at dealerships do not know how to fix it. It is a basic carburetor
jetting/tuning issue.
The BS40 CV carburetor used on the Savage/S40 was designed from the gitgo for economy and minimal exhaust emmisioins as dictated by the EPA.
This is NOT a performance carburetor by any stretch of the imagination.
Because of the EPA exhaust emmision requirements the carburetor is jetted and tuned at the factory to meet those EPA requirements which results in a very lean fuel/air mixture, and this causes the backfiring from this machine.
IT IS NOT A BASIC CHARACTERISTIC OF A LARGE SINGLE CYLINDER ENGINE dispite what some dealership lacky try to tell you. The solution is to tune the pilot air adjusting screw to find the best rpm for the engine at idle after a thorough warmup period. If the engine requires more fuel after trying to tune the pilot air adjusting screw, then the next larger pilot jet needs to be installed and then retuning the pilot air adjusting screw for best rpm.
This will result in the elimination of the backfiring, the engine will run cooler, will run smoother, and will have more power. The milage will likely be as good or better than before the fix. Some folks report a slight decrease in milage but this is usually attributed to their having a heavier throttle hand because they like the feel of the extra power and so want to run harder and faster.
If the stock exhaust/muffler is retained then just the tuning of the pilot screw us usually adequate to fix the problem.
If the stock muffler is removed in favor of a HD Dyna or Sportster muffler (very cheap on ebay) or a Supertrapp or Raask, etc, then rejetting the carburetor is certainly in order to maintain the proper fuel/air mix for most efficient running.
With a HD muffler on a stock LS650 engine the typical jets needed are a #52.5 pilot jet and #152.5 main jet, with the pilot air adjusting screw set at about 1.5-2 turns out (ccw from fully seated).
** For proper jetting and tuning the carburetor MUST be absolutely clean inside all the tiny passageways inside the carburetor body or it will not respond accordingly. Also, there must not be any air leaks in the exhaust system or the rubber mounting flange between carb and cylinder head or this will also cause/exasperate the backfiring problem.

This information is not theoretical; I have been tuning, jetting, rebuilding and modifying the BS40 carburetor for years for stock and modified LS650 engines. I know from experience what is required.

 

In my opinion, the best thing that you can do is enjoy the backfire. Think of it as an old time motorcycle (which it really is. A lot of the S40 is 1930's technology) Just ride it and enjoy it!

 

Unfortunately, a backfire problem can lead to engine damage if it is left to continue. The backfiring is due to a "too lean" fuel/air mixture which causes the engine to run hot, and the backfire is an uncontrolled explosion and that can over time blow a hole in the top of the piston ... NOT GOOD.
Bottome line is that a backfire is a symptom of something that is not right, regardless of what the turkeys at a dealership may say. The EPA tells them what they can and cannot do when tuning a carburetor; that is why the factory installs a brass cap over top of the pilot air adjusting screw...so it cannot be changed later..............what a bunch of crap.
If a carburetor is tuned properly it will still have acceptable exhaust emmissions and run a hell of a lot better.

 

Got used to the backfire every time shut down bike,at the pump it promotes conversation with other travellers.Question in my mind is,Does it cause any potential damage over time?