Change in exhuast sound and loss of performance

Discussion in '5th Generation 1998-2001' started by Busdoor, Sep 21, 2015.

  1. Busdoor

    Busdoor New Member

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    After a recent service to my bike, I've noticed quite the performance change...and not for the better.

    Here's a quick backstory:
    I have a 2001 VFR with a Staintune exhaust and PowerCommander III with just under 14k on it. I recently cleaned the oil sump screen and had to replace the oil pressure sensor thanks to some rodents who decided to chew through it, so to do both of these things I had the exhaust completely off the bike as well as the fuel tank, air box, and throttle bodies. I got the bike back together and everything seemed fine: bike started right up, sounded great, rode it around the block a few times, no issues. The next day I decided to ride it to work (about 25 mi) and roughly halfway there I heard the sound of the exhaust change (to a much lower tone) and immediately lost performance. The engine was still running smoothly and I still had decent throttle response but just a huge lack of power. On the way home the same thing happened.

    To me it seems as though it's somehow temperature related since it happens after the bike is warmed up. I thought that perhaps I didn't have part of the exhaust seated correctly and that as the pipes got hot it opens a leak around one of the gaskets but I couldn't find a leak anywhere. If it was an issue with the PowerCommader I would think it would happen on start up.

    This really has me scratching my head. If anyone has had this issue and can point me in the right direction I'd really appreciate it.
    Thanks!
     
  2. Knight

    Knight New Member

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    This sounds like a lack of intake pressure. Inspect the simplest things first such as the intake area for kinked vacuum lines or loose equipment.

    I am wondering if the PAIR valve is sticking while hot. Likewise check this equipment.
     
  3. Pliskin

    Pliskin New Member

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    I'm with Knight. Are the venting lines routed properly? Maybe you have one pinched or something, and once you actually ride the bike for a bit creating a vacuum in the tank, its not allowing it to vent properly. Short rides (around the block and such) wouldn't be adequate time to see this.
     
  4. Terry Smith

    Terry Smith Member

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    Good suggestion Pliskin, maybe the tank vent is blocked. Next time this happens, open the fuel cap, listen for a suck in of air.
     
  5. squirrelman

    squirrelman Member

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    Possibly one cylinder is dropping out. That would be due to bad coil connections, bad ignition coil, fouled sparkplug, or rodent-damaged plug wire. Try to locate one dead cylinder: cold header pipe or no change when removing plug wire or one plug that doesn't match the others.:mad-new:
     
  6. TNRabbit

    TNRabbit New Member

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    This. Can't think of anything else that would cause a drop in exhaust tone...
     
  7. sunofwolf

    sunofwolf New Member

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    ya chipmunk ate the wire and wanted it never to go again
     
  8. sunofwolf

    sunofwolf New Member

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    chipmunk ate wire so heshe woulf have a good home
     
  9. Underoath87

    Underoath87 New Member

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    You probably messed something up when reinstalling the throttle bodies. I recently removed my SV650's TB's and was having all sorts of problems (rear cylinder would cut out below 4,000 RPM). It ended up being that I didn't seat the rear TB into it's rubber boot properly, so there was no vacuum :/
     
  10. Knight

    Knight New Member

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    Busdoor, what up?
     
  11. CandyRedRC46

    CandyRedRC46 Member

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    I would do a compression test ASAP
     
  12. V4toTour

    V4toTour New Member

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    on a 14K vfr800? That's not even broken in yet.

    Most likely something he touched, possibly connection wise. When I was chasing down FI lights recently, there were instances when the bike would suddenly go into limp mode. This was occasionally accompanied by a FI light. The code corresponded with a faulty TP sensor. Felt like 2 cylinders had dropped out when getting on the gas, and the exhaust sounded different. However the bike was able to idle fine and otherwise smooth running exactly as he's describing.

    In my case I tracked it down to the ECM bouncing around. I guess there was enough play in the connector that it was throwing off the resistance readings from the throttle.

    Double check all connections and wire runs in the area you were working on.
     
  13. CandyRedRC46

    CandyRedRC46 Member

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    On a bike that you messed with the oil sump and it lost power, sounded and felt like it dropped a few cylinders? Yes I would do a compression check.
     
  14. V4toTour

    V4toTour New Member

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    his problem is intermittent. If he toasted some rings or something that would be all the time.
     
  15. codyc123

    codyc123 New Member

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    Something to think about, what if the auto choke/enrichment circuit is stuck on. Not really familiar with the wax unit though as I have a 98. Also compression issues tend to lessen as the engine heats up not get worse.
     
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