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Thread: LS650 Backfire

  1. #1
    Newbie
    Posts
    3

    LS650 Backfire

    I just bought a 2002 LS650 Savage and there is a small backfire on when you throttle down and even when you shut off the bike.

    Is there a easy fix for this or do i have to take it in someplace? Actully is it that big of a deal? From what i gather the Savage has a tendency to backfire.

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  3. #2
    Newbie
    My Bike(s)
    boulevard s40
    Location
    las cruces NM
    Posts
    14
    I just got an s40 and it has a tendancy to do little engine farts on occasion. From what I gather single cyl. bikes will do that. It shouldn't be anything major. Now if it occurs everytime you downshift or shutoff then it might need to be checked out.

  4. #3
    Seat Tester
    Location
    Toronto, Canada
    Posts
    74
    You can fix it by adjusting the carb. The mixture is very lean at low rpm.
    I own a Savage and I choose not to do it.
    I like it like that and it takes less gas. I know it will improve the performance, make the bike smoother, etc. but...

  5. #4
    Beer. Nature's Unstoppable Force.

    My Bike(s)
    '06 XB12X
    Location
    2040 N. Dale Mabry Hwy., Tampa, FL 33607
    Posts
    13,281
    Hope this helps:

    "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.

  6. #5
    Newbie
    My Bike(s)
    2003 Suzuki LS650 Savage
    Posts
    1

    Thumbs up Suzuki LS650 Savage Backfire

    Hi folks. I did exactly what the article that intimid8er posted. Not to bad a job and rode approx. 30 miles. I heard it make a small very low backfire once. The acceleration has dramatically improved. It also idles better. Temperature is cool here, about 50 degrees. It might make a difference when it gets hot again next summer. For now It was a success. Just a little info, you don't have to remove the carburetor, witch is a nightmare. Remove the seat, then the fuel tank and you have full access to the top side of the carburetor to remove the vacuum diaphragm cover. Its the large chrome looking cover with 4 screws. Once the cover is removed, the diaphragm lifts right out and you can get to the plate with the spacer down inside of the spring cup. Take care of the rubber and the long needle. Take note of how the plate down inside is positioned before you remove it. Once removed take out the plastic white spacer and reassemble. Pretty easy. As for the soft plug on the right side of the carburetor for the low speed mixture screw, you can carefully drill a small hole in the plug and screw a sheet metal screw into in and pull it with a pair of vise grips. Only drill through the soft plug. Remember, there is a brass adjustment screw behind it. Only run the screw in a thread or two so you don't damage the screw behind it. Any questions, email me @ fmezzo@twcny.rr.com

  7. #6
    Lost but forgotten

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    Welcome, and thanks for the great info. Nothing beats free power!
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