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Offline faizpakoh

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  • Town / City: Kota Bharu
  • Country: my
Afterfire on acceleration in high rpm?
« on: November 06, 2018, 11:37:24 AM »
Hi guys so i have this weird backfire/afterfire on acceleration on my z900. I just installed akrapovic full system last month, it does backfire @popping on decel which i found its pretty normal, but now after riding for couple of weeks i notice when im riding at higher rpm mainly in gear 4 at around 9k rpm when i let off the throttle for one sec and i start accelerate again i heard it backfire once. And it occurs everytime when i did it again. But i dont get the same backfire on gear 1,2,3,5 and 6.  What do you think causes this? Exhaust leak, too rich or too lean?

Offline bmartinZ900

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Re: Afterfire on acceleration in high rpm?
« Reply #1 on: November 06, 2018, 10:56:52 PM »
*Originally Posted by faizpakoh [+]
Hi guys so i have this weird backfire/afterfire on acceleration on my z900. I just installed akrapovic full system last month, it does backfire @popping on decel which i found its pretty normal, but now after riding for couple of weeks i notice when im riding at higher rpm mainly in gear 4 at around 9k rpm when i let off the throttle for one sec and i start accelerate again i heard it backfire once. And it occurs everytime when i did it again. But i dont get the same backfire on gear 1,2,3,5 and 6.  What do you think causes this? Exhaust leak, too rich or too lean?

I think you are confusing what a backfire vs unburnt fuel in the exhaust. I get the same symptom and can definitely attribute the cause being a small exhaust leak combined with a slightly rich condition. Some fuel is making it's way through the exhaust and when you open the throttle back up and introduce more air into the exhaust that fuel is igniting. From your prior post it looks like you have plugged up the AIS, so I would start looking for a leak, most likely around the collector. A small leak and the popping you described shouldn't be a huge worry. Have you had the bike tuned?

Offline Zrider

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Re: Afterfire on acceleration in high rpm?
« Reply #2 on: November 06, 2018, 11:08:17 PM »
My bike pops in between gear changes at high rpm. It sounds fantastic.

Offline mininsx

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  • Bike: Z 900, Concours 14
  • Town / City: Central Kentucky
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Re: Afterfire on acceleration in high rpm?
« Reply #3 on: November 07, 2018, 01:08:14 AM »
*Originally Posted by Zrider [+]
My bike pops in between gear changes at high rpm. It sounds fantastic.

My '08 Concours 14 with a TBR Carbon slip-on pops occasionally between gears, too.   :062:

Offline faizpakoh

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Re: Afterfire on acceleration in high rpm?
« Reply #4 on: November 07, 2018, 05:11:00 AM »
*Originally Posted by bmartinZ900 [+]
I think you are confusing what a backfire vs unburnt fuel in the exhaust. I get the same symptom and can definitely attribute the cause being a small exhaust leak combined with a slightly rich condition. Some fuel is making it's way through the exhaust and when you open the throttle back up and introduce more air into the exhaust that fuel is igniting. From your prior post it looks like you have plugged up the AIS, so I would start looking for a leak, most likely around the collector. A small leak and the popping you described shouldn't be a huge worry. Have you had the bike tuned?
My bike is still untuned

I just checked my collector again today and the nut holding it pretty loose which is weird, i double check it last month when i installed it and it already torque to spec :187:

Now the backfire is reduce a little bit about 20%, at higher rpm the backfire still there but somewhat reduce a little bit too...

Offline bmartinZ900

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Re: Afterfire on acceleration in high rpm?
« Reply #5 on: November 07, 2018, 05:26:24 AM »
*Originally Posted by faizpakoh [+]
My bike is still untuned

I just checked my collector again today and the nut holding it pretty loose which is weird, i double check it last month when i installed it and it already torque to spec :187:

Now the backfire is reduce a little bit about 20%, at higher rpm the backfire still there but somewhat reduce a little bit too...

It's not a backfire, although I understand that is the best way to describe it. It's just a symptom of a rich air fuel mixture with a full system. Perhaps you still have a small exhaust leak as well. No need to worry about either, and a proper tune will eliminate it

Offline faizpakoh

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Re: Afterfire on acceleration in high rpm?
« Reply #6 on: November 07, 2018, 06:25:34 AM »
*Originally Posted by bmartinZ900 [+]
It's not a backfire, although I understand that is the best way to describe it. It's just a symptom of a rich air fuel mixture with a full system. Perhaps you still have a small exhaust leak as well. No need to worry about either, and a proper tune will eliminate it
its weird because on my other bike even in higher rpm i do get backfire but it happen when i closed the throttle, not when i open the throttle again  :027:
o well tomorrow i will disassemble my pipe again and double check for air leak between the connection

Offline Downtown

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Re: Afterfire on acceleration in high rpm?
« Reply #7 on: November 08, 2018, 02:05:20 PM »
*Originally Posted by bmartinZ900 [+]
It's not a backfire, although I understand that is the best way to describe it. It's just a symptom of a rich air fuel mixture with a full system. Perhaps you still have a small exhaust leak as well. No need to worry about either, and a proper tune will eliminate it

Is it a problem if i run with rich air fuel mixture? I have full system and not interested in remapping or tuning.

Offline bmartinZ900

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Re: Afterfire on acceleration in high rpm?
« Reply #8 on: November 09, 2018, 02:13:03 AM »
*Originally Posted by Downtown [+]
Is it a problem if i run with rich air fuel mixture? I have full system and not interested in remapping or tuning.

You won't have a problem with the stock fueling being a tad rich. A leaner AF will make more power with a proper tune (aprox 8-10hp) over stock. But as far as the motor, rich = safe and lean is mean.