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Thread: 72 xs650 backfiring

  1. #1
    Settled In cam1765's Avatar
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    Unhappy 72 xs650 backfiring

    Hello this will be my first post and unfortunatly a bad one. I have a 72 xs 650 that backfires when decellerating and pops a little while idling. Also it takes it a second or two to respond when the throttle is turned. Doesnt backfire or pop during accel. Once the bike responds it takes off. I recently just put new needle and jets in it also. And I had to adjust the floats because of overflowing. If anyone can help I would greatly appreciate it.

  2. #2
    Very Active Member betabilly's Avatar
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    Unburned gas released in the exhaust causes the loud backfire pop. The bad part is the excessive wetness dilutes any oil coating on the cylinder walls causing wear.....
    LOUD pipes saves lives!

    '73 RD350A
    '86 YX600
    '07 V Star 650 Classic

    Yamaha RD/AC, ride it like you stole it!

  3. #3
    Settled In cam1765's Avatar
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    I think i have an air leak around my intake could this cause the problem?

  4. #4
    Permanent Fixture bigwater's Avatar
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    Quote Originally Posted by cam1765
    I think i have an air leak around my intake could this cause the problem?
    That may be your problem, it could be causing the bike to run a bit rich. It needs to be fixed either way. If that doesn't fix it, take a look at your exhaust.

    A manifold leak will cause air to be sucked back into the exhaust system due to loss of back pressue when decellerating using the engine as a brake. This will confuse your oxygen sensor, and cause more fuel than is needed to be dumped into the cylinder. This causes more of a stuttering or sputtering than an actual backfire... it's sort of a repeated quiet pop instead of a loud bang.

    Easiest way to check it out is when you're decelleratin with the clutch OUT and it's making the popping noise, Pull the clutch IN. If it's a manifold leak, the popping will stop.
    Last edited by bigwater; 08-24-2005 at 11:51 AM.
    Never twist the throttle with your ego

  5. #5
    Quote Originally Posted by bigwater
    ...This will confuse your oxygen sensor...
    I owned a '72, in 1972. There is no oxygen sensor on that bike.

  6. #6
    Permanent Fixture bigwater's Avatar
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    Okie Dokie then... I guess I need to pay better attention to the post headers and not open my mouth before I swallow my entire leg, foot and all.

    The advice still holds true though... Maybe somebody else will get some benefit out of it.
    Never twist the throttle with your ego

  7. #7
    Sorry for sounding like a jerk in my reply. I wasn't trying to nail you or start something. I started typing and got grabbed by SWMBO for some chores, so I fired off what I had, and I shouldn't have. Your advice is right on the money - the bike can not, will not run right with a manifold leak, and if it has one it has to be fixed.

    Quote Originally Posted by bigwater
    Okie Dokie then... I guess I need to pay better attention to the post headers and not open my mouth before I swallow my entire leg, foot and all.

    The advice still holds true though... Maybe somebody else will get some benefit out of it.

  8. #8
    Permanent Fixture bigwater's Avatar
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    No problem jackndeanie. You didn't come off as a jerk... you simply came off as somebody who knew what he was talking about and was stating a fact. There's not a whole lot of room on these types of boards for syrup or worrying about feelings. I didn't think twice about it.

    BTW, Welcome to RiderInfo. Hope to see you around often!
    Never twist the throttle with your ego

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