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Excessive Popping on Decel


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I've got a weird issue that's been happening for a while, I just haven't done much about it. Off the throttle, I think it's too rich & fuel is passing through into the exhaust and goes BOOM. This isn't decel gurgle. These are BOOM's. With ear plugs in, it's loud enough to be unpleasant. 

Model year 2015
Full Akro
2WDW flash
Valves adjusted after this started happning, no change
Throttle bodies synced at the same time, no change

I install exhaust in 2017, had it flashed in 2018. After both of these, there was only the tiniest amount of decel gurgle. This started in late 2019, early 2020.  Therefore, I don't think it's an issue with the flash or exhuast, but something is loose or broken. 

Things to check?

'15 FJ09

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Still have AIS?
I don't know if exhausts these days still have packing in them, might be slowly deteriorating, thus more pull through and possibly leaking through AIS plumbing?

Big shot in the dark on that one.


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+Definitely AIS function and aftermarket exhaust.


most bikes you can just block off the air feedpipe that goes from the airbox to the ais system. The easiest way is to pull the pipe off the stub at the airbox and put something in/on there [like some thick polythene - not thin, the petrol atmosphere will dissolve it] or use a ball bearing. What ever you use make sure it cant move.

I done it this way on several bikes and it always sorts it - you can do a full ais-delete when you have to do a valve job or similar.

Edited by pilninggas
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If you want to “try the solution before buying”, you can reach in there with a long angled hemostat and clamp shut the airline to the AIS (LH side line, NOT the center vent line that runs to the valve cover.) go for a ride and see if it fixes it. 

next, check to make sure all your TB’s are seated properly in the intake ports and that the Caps on the sync nipples aren’t torn or have a pinhole leak. 

If still no change, pull the headers and replace all 3 exhaust gaskets making sure the pipes are seated correctly before snugging up the clamps. 


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  • 2 weeks later...

I also have the full Akro on my 2017 and it pops and crackles on deceleration but I haven't done any flashing or other changes from stock. I actually like the sound. In fact if I accelerate gradually and hold the throttle closed for a second between gear changes it will also give a pop. 

What is this AIS of which you speak?


Edited by andz
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@andz, on top of the cylinder blocks are small mechanical valves that scavenge gases. They are controlled by an electronic valve and on deceleration extra air is bled into the mix so that unburnt fuel is diluted before it goes through the exhaust. After market exhausts seem to screw up this system so you get pops and bangs from the excess fuel in the hot exhaust. 

ECU flashes often disable the electronic AIS valve to stop this, presumably because you can damage the exhaust over time, but you can also remove the little mechanical parts and replace them with blank-off plates, as well as remove the rubber piping.

It seems to be good practice to do something about the AIS when you fit a higher flow exhaust, even if the supplier claims you don’t have to. My Scorpion slip-on claims to need no changes, but runs better with an ECU flash and I fitted AIS block off plates to finish off the changes.

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Red 2015 Tracer, UK spec (well, it was until I started messing with it...)

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