Question about 2005 Suzuki Boulevard S83

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Engine starts back firing. When I check the plugs, the back cyl plug is black. Tells me fuel but should be missing instead of backfiring. Could the resistance from the plug be causing the plug wires to cross fire? If so, how do you change the plug wires and can you? If I exchange the front and back spark plugs, the back fire stops for another 1,000 miles.

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  • Zaraki Sep 13, 2010

    That sounds like a carbon fouled spark plug if it is black and kinda dry and powdery, and either the engine has been ran with the choke on, the air/fuel mixture is way too rich for that cylinder, or the spark plugs are the wrong heat range for that engine. If the spark plug is black and wet with oil then the problem will be oil getting into the cylinder most likely through a valve guide or a worn out piston ring. Changing the spark plugs around and the engine runs alright for 1000 miles would indicate that the ignition coil is working, and that it takes approximately 1000 miles to foul out the spark plug, and that is more likely a mechanical problem than an electrical one.

  • ron_stinson_ Sep 13, 2010

    I agree the plug is fuel fouled. But wouldn't that cause the engine to miss, not backfire? It is still running on both cyl but it backfires inconcistantly while it is running. As soon as I clean the plug or exchange with the front plug the backfire stops? The plug is not wet, just black. It still has a good gap and no burnt oil?

  • Zaraki Sep 13, 2010

    Carbon on the spark plug unlike oil or other deposits does and will conduct electricity, (a lot of people do not realize that, but in-fact it is a very good conductor of electricity) so the secondary voltage will not jump the spark plug gap consistently if there is carbon on the spark plug, and the secondary voltage will be drawn off from the center electrode of the spark plug because of the carbons ability to conduct electricity. Because the spark plug is getting carbon fouled the amount of carbon building up in the combustion chamber and around the valves will soon keep them from closing properly and that will also cause a back-fire problem of its own. The suspect would most likely be the carburetor or fuel injector for that cylinder is causing a too rich condition for that cylinder.

  • ron_stinson_ Nov 09, 2010

    So I wrapped the plug wire and boot with black electrical tape. Just got back from Florida trip, 2500 miles, with no problems what so ever. This is a nice bike.



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On you motorcycle the wire is part of the coil and there are two coils. Either you have a bad coil, a bad spark plug , or a bad spark plug cap. NGK makes some spark plug caps for about $5 each. Replace both of your spark plug caps and spark plugs. This should solve your problem.

Posted on Sep 13, 2010

  • David Belcher
    David Belcher Nov 09, 2010

    If you run a fuel system cleaner specifically Chevron Techron before your next oil change you can clean your valves, combustion chamber, pistons, and carburetors all at he same time. Afterwords do a valve adjustment just to check that part of the problem might be an exhaust valve that is too tight.



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