S40 / Savage backfiring

[Flugondus]

I got a 2005 S40 and it backfires every time I turn the motor off(when the killswitch is used or the stand gets pulled out). I was slowly starting to get worried about that. Mybe somebody else had to do with the same problem or heard about it??

[intimid8er]

Perfectly normal amigo.

I'll explain what's going on later.

[sunny]

that's just the way it comes from the factory.

there are two things you change on and in the carb to get rid of it, but if you like the way it rides then i wouldn't change it.

the older ones were far worse even backfiring on any quick rolling off of the throttle. the newer ones seem to only have it when turning it off.

[intimid8er]

Originally Posted by intimid8er

Here is an article I have for the carb mod.

"Savage Backfire
(from January 1997 RIDER magazine's Tech Q&A)

Q) I purchased a new Suzuki Savage 650 last July. From the very beginning the motorcycle would backfire when decelerating or coming to a stop. I took it back to the dealer twice before the 600-mile service, and complained about it at the initial service. I have tried different grades of gasoline and they seem to have no effect. The dealer has told me that I should expect backfiring with the design of this engine and that it should decrease as I build up mileage. I have 900 miles on the bike now and backfiring doesn't seem to be decreasing. I have found other riders of Suzuki Savages that are having the same problem. - Jay Coney, Kerrville, Texas.

A) This column receives a lot of mail over the course of a month, and the single biggest gripe among our readers are problems with lean-running. late-model carbureted bikes.

The poor old LS 650 really suffers at the hands of the EPA, and I certainly sympathize with you, Coney. We can fix it, but first let me explain the hows and whys.

When the throttle of any engine is rolled or snapped shut, some fuel is drawn through the engine and kicked out the exhaust without being burned. In abundance, this raw fuel vapor can be smelled, tasted - and when light is passed through it- seen. It's referred to as photo-hydrocarbons or more commonly smog. Yes, there are several other pollutants coming out of the exhaust, but the human senses can't detect them. The manufacturer of motorcycles have three methods of dealing with excessive hydrocarbons. Forcing air down into the exhaust port with an air pump and diluting the outgoing fuel vapor is one method. Kawasaki pioneered this method with their 'Clean Air System', which employed a vacuum-driven pump that puffed air through reed valves placed over the exhaust system. A 'cat' is nothing more than an oven which bakes the hydrocarbons, burning them off.

The most common method is to simply lean out the carburetor. The low-speed and midrange circuits of the late-model carburetor are not adjusted to give optimum performance - they're set up to produce a minimum hydrocarbon count on deceleration. What miserly amount of fuel they do deliver to the combustion chamber when the throttle is closed causes misfire and an audible afterfire in the exhaust pipe.

Now, I haven't mentioned fuel injection or other exhaust gases. As I said, the bulk of complaints from readers of this column is deceleration backfire and also poor idling of carbureted engines. No doubt we'll get around to discussing other emission-control devices and their problems in future issues.

Getting back to your Savage 650, Coney, here's how we can specifically cure its problem. We need to richen those two areas of the curburetion curve that are factory set on the ridiculous side of leanness. Remove the diaphragm slide from the carburetor and look down inside its bore. Two small screws hold a plate over the slide needle. Removing the plate, you'll see a small, white plastic spacer with a hole through it sitting on top of the needle. Throw that spacer away and reinstall the plate. A spring under the needle clip will now push the needle up to the plate occupying the space vacated by the white spacer. The distance that the needle has been 'lifted' is the thickness of the discarded spacer - and that's ideal. With the needle raised, more fuel will flow by it, meeting the actual needs of midrange running.

We can also fatten up the low end of your bike's carburetor by turning out the low-speed mixture screw. To gain access to this screw, you'll need to drill out the brass plug pressed in over it and yank it out with a sheet-metal screw attached to a slide hammer. You'll find that plug up high on the right side of the carb about where the mouth enters the carburetor. Usually Suzuki applies a splash of white paint over the brass plug so that it's immediately noticeable. With the engine warmed up and idling, turn the mixture screw out incrementally until you achieve the highest idle. There will be no doubt in your mind that you're making progress because the idle will come up and sound stronger. At this point, turn the idle adjuster knob out and bring the idle back down to a leisurely gait.

Just these two, relatively simple adjustments will not only eliminate the backfire, they will make an amazing improvement in throttle response and driveability." (End of article)


Some folks have gotten varied results by experimenting with the size of the spacer. They have either milled their own, or gone to Home Depot and found something of similiar size and construction, and went with something half the size of the original spacer with excellent results.

The big deal though is adjusting the low speed mixture screw. The hard part is drilling out the plug. Be careful..... Ideally when the screw is exposed, you want to turn the screw in until it is just meeting resistance at flush, then mark the top of the screw, and then turn it out two and a half turns from where you marked it. Adjust your idle accordingly. If I remember, it is 1100 rpm.

[dichotomous]

www.suzukisavage.com
nice forum very specific to our bike. search through there and ye shall find that which ye seeketh. actually I've tried a couple of the more common mods on there and they worked nicely so dont be too shy, then again I have no warrenty to void so thats something to think about.

[diamond_jim]

I just did the carb mod tonight on the S40. I took pics but I'll post them later as my wife is on my laptop and I'm on hers at the moment. After the mod, I took a ride to Lowes to get the spacers and longer M6 bolts to do the seat mod where the front of the seat is raised via spacers.

The carb mod makes a significant difference. More power across the whole rpm range and very noticeable when cruising about 50-55mph in 5th and you roll on the throttle to pass a cager. It didn't do much for the backfiring though. Of course, the backfiring wasn't and still isn't too often. Only when I decel/engine brake for more than maybe 4 seconds.

It's amazing how fast the bike gets up to 60mph so quickly without it seeming to stress the engine at all. Also, there's a long, big hill on highway 31 that I ride on everyday. I noticed a difference between the M50 and the S40 after the carb mod tonight. When I'd go up the hill in 5th on the M, halfway up the hill I'd have to give it a little more gas to maintain the same speed. Not with the S40 though. It seems to stay the same speed without having to give any extra throttle. The bike is about 15-18 horsepower less than my old M but I guess weighing 200 pounds less helps out a good bit.