Decel Popping Causes & Solutions

Posted by Bare | Last Updated June 30, 2013

This article is written for those of you having problems with exhaust decel popping. These are things you can do or check to help solve this problem outside of just desmogging the motor. One thing a lot of motorcycle owners don’t realize is that there was probably decel popping with the OEM exhaust, but due to the restrictive baffling of stock exhaust systems you never heard it. By changing exhausts to get a little more “roar” there has also been an increase in the loudness of decel popping.

  • First and foremost – when you slow down let go of the throttle completely. Train yourself to close the throttle when you are decelerating – a half open throttle causes popping.
  • On FI bikes DO NOT “blip” the throttle when decelerating. Doing this will cause popping and fool the ECU into thinking you are accelerating thus compounding the problem. FI engines depend on many sensor inputs to tell the ECU how to respond, by “blipping” you are tricking the ECU into thinking the engine is doing one thing while you are actually doing another.
  • Check the exhaust pipe for leaks at the header gaskets and if you have a 2 part pipe (muffler and headers are 2 separate parts) check the band clamps and gaskets there. You can do this using smoke, so get out the incense, cigarettes, cigars, etc or just blow out a match – and with the bike running pass this smoke around the exhaust ports and/or the junction of the headers to the muffler. If there is a leak you will see the smoke either get sucked in or blown around. If there is a leak ask yourself:
    • When/if you changed or removed and reinstalled the exhaust did you remove the old crush gaskets from the header ports (yes they ARE in there) and install new ones? These crush gaskets are not reusable items, just because you only put 5 miles on them does not mean they are still good. Crush gaskets like these are designed for one-time use – once they are installed they are crushed and become “used” and cannot be used again.
    • Did you torque down the header bolts to the appropriate torque and then retorque them after riding a few times? Check them again to make sure they are still torqued to spec.
    • On a 2 part exhaust are the band clamps (where the muffler and headers meet) torqued down to the appropriate ft/lbs? Check them again to make sure they still torqued to spec.
    • Is the header pipe sitting square in the exhaust pocket? Sometimes it appears they are when they aren’t. You can verify this kind of exhaust leak by looking for carbon trails.
    • If you’ve changed exhausts did you check that the header acorn nuts didn’t bottom out before the header flange tightened properly to seal pipes into the head? Some aftermarket exhaust systems have thinner exhaust flanges so you may need a washer under the acorn nut to make up the difference.
  • Be sure the throttle body/carb butterflies are closing completely. You can do this by removing the air cleaner and pushing on the butterflies with your finger. There should not be any movement at all. If they do move close then check all throttle cables and adjust accordingly.
  • A throttle body/carbs that are out of sync can cause popping and uneven idling. This adjustment takes a special tool and if you are not confident working on the throttle body it may be best done by your dealer. Link – VTX 1800 Sync
  • If there are no leaks in the exhaust then check for leaks in the smog system. Are all the hoses snug and in place? Are all the hose clamps snug and holding the hoses where they belong? If you’re not really tied to the smog stuff being there I would recommend removing it entirely to prevent this from even being a possibility (desmogging the bike usually fixes about 95% of decel popping). Link – VTX 1800 desmog / VTX 1300 desmog

If you’ve gone over all of the above and still have popping then you need to look at fuel managers:

  • If you have a Power Commander are you sure your map is dialed in for your bike? If you know it is (because you have tested it on a dyno) then the popping may be a sign of a normal running engine (it’s not always a sign of a poor running engine). In this case the only solution to stop the popping is to add a little more fuel in the appropriate “cells” on your map (it should be cells in the zero throttle position) and this will cover up the problem. You should only add about 2 points of fuel at a time, test ride it and if you need more then add it – the idea is to fix the problem without dumping huge amounts of fuel and hurting the MPG. You should be aware that if your map was made or tested on a dyno to work for your bike then you will actually be detuning your bike doing this.
  • If you have a closed loop (self-adjusting) fuel manager there’s not much you can do. Ride it after making all the necessary checks mentioned above and see if the problem works it’s way out (maybe you had a small leak causing the problem). If the problem persists then I would consider disconnecting the unit and see if it makes a difference. Some of these units can be opened, if you can open yours then do so and check for corrosion buildup or loose connections by removing and reseating any plugs. Also make sure the O2 sensor is snug in the exhaust pipe and all other wiring connections are good. If you made connections using vampire clips then read this and remove them.
  • If you have a TFI, FI2K, or any of these other “pot style” fuel managers then this is a tricky situation. These units are designed to make broad changes in the air/fuel ratio by increasing the width of the fuel pulse signal sent to the fuel injector by the ECU. They cannot lean out the air/fuel ratio, they can only make it richer and they cannot make detailed, specific adjustments like with a power commander unit. My best recommendation is to VERY slightly bump the lowest “pot” on the unit up ever so slightly and test it out. If you’re still popping then bump it VERY slightly again – these units don’t take much adjustment to make big changes in your A/F ratio and you want to try and maintain fuel mileage in this process so take it slowly.

6 Responses to “Decel Popping Causes & Solutions”

  1. […] Take a look at this article. What happens when you close the throttle (completely) on decel? […]

  2. Dave Harris says:

    EXCELLENT article.
    Thank you for taking the time.
    My problem is exhaust leak.
    Would not have figured it out without this article.

  3. Mike says:

    Same here. I would have never figured out that my exhaust bolts were loose and that was causing the popping. Thanks for the info!

  4. Rick says:

    thanks for the info i really do appreciate it

  5. Steve Whittingham says:

    Good comprehensive article and not only for Harley owners. My problem was on a Honda C90 Cub. Thanks very much for taking the time and sharing the knowledge.
    Steve W. (Spain)

  6. Nitin Sharma says:

    Hi. Since i work on customising bikes, face this problem a lot. One solution that we achieved in few bikes is changing the air filter. A heavy breather mostly do the trick. I think it helps to achieve the A/F ratio right.

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