Backfiring at start up

Discussion in 'Dyna Models' started by nupicasso, Nov 18, 2008.

  1. nupicasso

    nupicasso Member

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    Hey gang,

    I just recently put a pair of cycleshack pipe, SE Stage 1 air cleaner and power commander on my 08 Street Bob... everything has been fine...then...over the past couple of days it has been backfiring at start up. It wont do it every time...but most of the time. I have to laugh, cause the first time it happened, it caught me so off guard that I literally jumped a few feet. It sounded like someone fired a 45 at me.

    Anyone have an idea why this might happen? And could this happen if there's an exhaust leak.(they were out of the regular exhaust gaskets, so I picked up a pair of the screamin eagles...which I heard weren't very good)

    Any help would be much appreciated.
     
  2. TQuentin1

    TQuentin1 Well-Known Member Staff Member Moderator

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    OK, so the exhaust change was for full pipes, not just slip-ons, right? Were the SE gaskets the soft metal impregnated with wire mesh? Did you seat the gaskets all the way inside the heads' exhaust ports? Also, double check that the exhaust bracket holding the pipes against the heads are tight. Make sure that the "snap rings" that let you compress the pipes against the heads have not partially or completely slipped over the flange on the head end of the pipe. Also, we had a user that had the flanges SEPARATE from the pipe! If all that checks out, grab the pipes (cold) and see if you have any "play" at the heads. Then fire up the bike and make sure there is no exhaust leak along the length of the pipes.

    If that all checks out, grab a can of WD40 and spray some around the intake manifold to see if you have any leaks there. If you do, the engine will lug when it breathes in the WD40. BE CAREFUL THOUGH!! THAT STUFF IS FLAMIBLE.

    Let us know.

    TQ
     
  3. nupicasso

    nupicasso Member

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    Thanks for such a quick response.

    The gaskets are the ones that look and feel like mini brillo pads...as opposed the the normal ones that kind of look and feel like aluminum wrapped wiring.

    I won't be able to get out there and really take a look until tomorrow after I get home from work. My neighbor will have to deal with my bike scarin the beJesus out of them an 6am for a few more days! lol.

    But...It will be nice if it's a simple fix...
     
  4. TQuentin1

    TQuentin1 Well-Known Member Staff Member Moderator

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    Right. In the morning BEFORE you start it, grab the pipes near the heads and see if they are loose at all. If they won't budge, good. Over the weekend, you might want to change out the crush gaskets for the lead looking ones with the wire mesh.

    TQ
     
  5. glider

    glider Veteran Member

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  6. nupicasso

    nupicasso Member

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    Hey Glider,

    I do this with the air cleaner off, right?
     
  7. glider

    glider Veteran Member

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    Yes with a squirt bottle and keeping the RPM's up a bit.
     
  8. nupicasso

    nupicasso Member

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    So Glider,

    Do you think a build up of carbon is attributing to my problem? Or is this just to clean the result of the problem?



    The thing that baffles me is that when it comes to the exhaust I go by sound and feel. I know when she sounds good...when she sounds lean...when she sounds rich...but when I put the pipes, filter and air cleaner on...she was just right. Now...she's runnin a bit rich. I thought this EFI rubbish was supposed to make things easier...and more constant. LOL

    Thanks for your reply Hobbit.

    How is it riding around the UK?! I travel to Ireland quite a bit...was thinkin about renting a scoot once I got out there....and then possibly taking a jump over to England.
     
    Last edited by a moderator: Nov 19, 2008
  9. glider

    glider Veteran Member

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    Any internal combustion engine can build up carbon depending on how it's driven and other factors too. It's best to eliminate the possible sources first before trying to find a cure. Carbon can cause some strange things like detonation and actually raise compression when it builds up enough and cause pinging. This is only one step in cleaning things up and a start to finding out why it's popping back on startup.
     
  10. nupicasso

    nupicasso Member

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    Ah.

    I was also planning on putting a little seafoam into the fuel(which i do every few thousand miles) This also cleans up carbon as well from what I understand... as well as cleaning out water from the tank.