will a free flow exhaust lean out the bike

Discussion in 'The Garage' started by motorat, Feb 3, 2013.

  1. motorat

    motorat TBD

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    if i install a free flow exhaust on an efi bike could it lean out the bike or should the efi compensate?

    thanks
    #1
  2. mcma111

    mcma111 Long timer

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    Yes. The FI program is set for the OE exhaust. Change the exhaust and you'll need get it reprogramed..
    #2
  3. motorat

    motorat TBD

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    thanks.
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  4. concours

    concours WFO for 41 years

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    Well, sometimes. The bike on your signature, is a "closed loop" FI system, it monitors the exhaust gases with an O2 sensor and can trim the fuel delivery as needed. The slight change in flow will be easily compensated. No need to reprogram the the ECM. Now, here's the fun part. The bike is fueled very lean for emissions reasons, so re-mapping may give better low speed drivability.

    The early bikes (and some off-road bikes) had an "open loop" system, whereby the ECM had a simple fuel map based on RPM and throttle opening. (my '03 Victory TC comes to mind) Those could be fooled by changing the plumbing (exhaust pipes).
    #4
  5. JimVonBaden

    JimVonBaden "Cool" Aid!

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    There is no definite answer unless you state the bike. On the BMW R1200 series it shows little, if any, tendency to lean it out. The fueling and ignition systems tend to compensate for these changes.

    Jim :brow
    #5
  6. LuciferMutt

    LuciferMutt Rides slow bike slow

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    Yes. Maybe. No.

    There, covered all the bases. :deal

    Seriously, though, if it's the bike in your sig, it will be fine without any ECU changes.
    #6
  7. caryder

    caryder Been here awhile

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    If the EFI system uses an O2 sensor for feedback, it only operates closed loop over a limited RPM and throttle opening range. While it's operating closed loop it tracks AFR adjustments based on O2 readings and remembers a % value to lean or rich up the map when in open loop (such as during acceleration when the AFR is outside the measurable range of a narrow band sensor). The point is, the map is fixed set of values with a multiplier based on closed loop (i.e. cruse settings). If your EFI only has pressure and temp inputs, it is effectively open loop all the time meaning the ECU has no idea what the AFR really is. Your maps were developed with the stock exhaust and intake. There is little point in modifying exhaust or intake without also modifying the maps. You may discover lean spots (surging) and burble or popping during decel. At least if you remap, you will know it is correct for your setup.


    Chuck
    #7
  8. motorat

    motorat TBD

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    the bike is a 2012 royal enfield with 4800 miles. it has a basic efi system (with an o2 sensor) on it and i installed a d&d exhaust system.
    the d&d is open with just some packing in the slip on. the head pipe diameter is larger than the stock. it ran fine for about 1000 miles then developed what i thought were fueling problems. so i brought this up on the royal enfield forum. they said it was water in the gas. there is no water in the gas, i have added heet on one tank, sea foam on another and drained the tank and put in fresh gas and it still behaves the same way. i also put the gas from the RE into my tractor and it ran fine.

    i had surging and a feeling of running out of gas also loss of power--and when you are starting from low power and then loose more it is noticable.

    since the bike was still under warrenty i brought it to the dealer, a 4 hour drive one way.
    after a careful examination of about 30 minutes with no test ride the service manager said that it was running too lean
    and it was because the after market exhaust had no back pressure and was too free flowing

    i am just a change the oil and bolt on parts kind of guy.

    well i put it all back to stock and it still has the running out of gas/surging.


    luckily this is not my only bike.

    thanks for your replies.
    #8
  9. HapHazard

    HapHazard Waiting for Gudenov

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    Sounds like you've taken the right first step in returning the exhaust to stock. Seeing as it is behaving the same (and me not knowing anything about RE EFI systems:lol3), I'd suggest unhooking the battery overnight - which hopefully will reset the ECU (this works on a Chevy truck - how different could they be?). Hook the battery back up the next day and see what happens.

    By your description of how the bike ran OK for 1000 miles and then developed the problem would seem to rule out the exhaust (to me, anyway). If you can pull the fuel line off the petcock and see if the gas flows out freely (you might have to use the petcock's "prime" position (if it has one), or apply vacuum to the vacuum port (if it has a vacuum petcock with no prime position). You might have an obstruction in the tank outlet or valve.:dunno

    Good luck, and let us know how you do.
    #9
  10. CycleDoc59

    CycleDoc59 Wrench Rider

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    I see this quite a lot; owner wants more noise, changes exhaust and a mess results.
    Motorcycle engine design and set up is tricky; mfg has to get power w/out noise, w/out
    unlawful emissions, good fueling with decent gas mileage...etc.

    It's somewhat of a recipe, like making a cake; get the recipe right or it can be hard to
    eat (or ride). So, anytime any part of the recipe is changed, something else changes,
    sometimes for the better, sometimes not...

    Yes, there is a little compensation built in, and some exhaust changes on some bikes
    work fairly well with nothing else needing to be done. In the case of the Enfield, a few
    years ago the muffler size was increased and a cat installed, making it a large and vital
    part of the recipe. It's very hard to quiet the exhaust of a single; one huge "boom" at a time.

    So that change to an unbaffeled straight thru D&D was a huge change. Installing a unit like
    the Techlusion, if one is available, would likely solve the problem, enabling more fuel to be added.
    But open exhausts can change the power curve, often killing some low-end torque. Dyno
    tuning, or at least a "check run" on one is not too pricey, and can save a lot of grief.
    #10
  11. CycleDoc59

    CycleDoc59 Wrench Rider

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    Oh, I see I left out the part about burnt exhaust valves and damaged cylinder walls...
    #11
  12. LuciferMutt

    LuciferMutt Rides slow bike slow

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    Dude....the OP is still having problems after returning to the stock exhaust.
    #12
  13. anotherguy

    anotherguy Long timer

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    The excessive heat may have damaged the O2 sensor. Are there provisions for code reading on the Enfield?
    #13
  14. rapidoxidationman

    rapidoxidationman Easily trainable

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    ^^^ burned exhaust valves


    Ya, that makes sense. Stock exhaust wouldn't fix burned exhaust valves.

    Time for a compression check?
    #14
  15. motorat

    motorat TBD

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    the bike will start and run fine for about 1/4 mile. then when excellerating it has the feeling of running out of gas.
    it really feels like it has a fuel filter that is clogged. when rolling on the throttle it is being choked then on roll off it kind of regains some power then on roll on it looses it. in the shop manual i found 2 filters on on the fuel pump and one on the intake to the injector. i think it might be one of those......neither is easy to get to. i just have to find a shop that will try to locate the problem.
    #15
  16. HapHazard

    HapHazard Waiting for Gudenov

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    It is possible that the bike switches from closed loop (preprogrammed maps) to open loop (O2 sensor and other sensor readings) after the quarter mile. As anotherguy suggests, can you read any codes? Is the shop manual decent? Does it have an EFI troubleshooting section? I wouldn't rule out the filters, either.
    #16
  17. southern cross

    southern cross WARDY

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    Running fine for 1/4 mile then feeling its running out of gas maybe the problem. This symptom is typical of the tank breather tube being blocked. After 1/4 mile just undo the fuel cap for a moment. Many times before this has been the simple fix after op looking for more exotic probs. first. Hope this may solve the prob.

    S.C.
    #17
  18. anotherguy

    anotherguy Long timer

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    Step one:check fuel pressure.
    #18