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Discussion Starter #1 (Edited)
Okay, I know there are about a zillion and a half threads on here about backfiring and popping when letting off the throttle, but I'm getting frustrated.

When I had the stock "punched out" exhaust with the Arlen Ness Big Sucker I was able to tune the PC III and get rid of the problem. I just recently installed Cobra Speedster Slashdowns. I've tried every map available on the Power Commander website for the VN 900 and tried tweaking it myself, but just can't get rid of the back fire.

It happens when I accelerate and then let off the throttle. If I roll off it rather than release it, its better, but still there.

I know I should get it dyno tuned, but the wife is threatening to castrate me if I spend anymore more money on the bike right now.

My question is - does anyone have the same setup as I do and have a map for the PCIII that got rid of this annoying problem?

My setup is

07 VN900 Custom
Arlen Ness Big Sucker Intake (I think the BAK is probably close enough to be the same)
Cobra Speedster Slashdowns
Power Commander III

And I've already marbled it.

Thanks so much to anyone that can help.:)
 

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I have a custom map I can forward to you. PM me your email. Tried all the stock maps and this one is best so far.

Frank
 

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Discussion Starter #5
I have a custom map I can forward to you. PM me your email. Tried all the stock maps and this one is best so far.

Frank
Biohazzmat - sent you a note. Thanks for the help.
 

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Already marbled it when I first installed the intake.
Did you change out the O ring exhaust gaskets? Sounds like an exhaust leak is sucking in air and causing the decel popping. Spray WD40 around the exhaust flanges while the engine is running and see if white smoke comes out the pipes. If that doesn't show any leaks then change the value in the zero throttle position column cells, starting at 1500 RPM up to redline, from 0 to 20 or 30 then save the map.
 

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Discussion Starter #9
Did you change out the O ring exhaust gaskets? Sounds like an exhaust leak is sucking in air and causing the decel popping. Spray WD40 around the exhaust flanges while the engine is running and see if white smoke comes out the pipes. If that doesn't show any leaks then change the value in the zero throttle position column cells, starting at 1500 RPM up to redline, from 0 to 20 or 30 then save the map.
Sojourner - I changed the O-rings when I changed the exhaust. I'll try your WD-40 trick and see what happens. Thanks for your help.

On that note, I was surprised that the stock front header bolts were loose when I took them off. They had been loose long enough for some rust to have formed. This is odd sense I've never had the stock exhaust off before I put the Cobras on.
 

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Discussion Starter #10
Did you change out the O ring exhaust gaskets? Sounds like an exhaust leak is sucking in air and causing the decel popping. Spray WD40 around the exhaust flanges while the engine is running and see if white smoke comes out the pipes. If that doesn't show any leaks then change the value in the zero throttle position column cells, starting at 1500 RPM up to redline, from 0 to 20 or 30 then save the map.
Sojourner - I already have that column set to 10 because that worked well when I installed the Arlen Ness but still had stock pipes. I'll try raising it, but I'm confused. Pardon my ignorance, but I thought that backfiring in the tailpipe was caused by running rich. The unburnt fuel enters the tailpipe and explodes when it comes in contact with the hot pipe. If I add more fuel won't it make the condition worse? I'll try it because it seemed to work with the stock exhaust, I just don't understand it. :)
 

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Sojourner - I already have that column set to 10 because that worked well when I installed the Arlen Ness but still had stock pipes. I'll try raising it, but I'm confused. Pardon my ignorance, but I thought that backfiring in the tailpipe was caused by running rich. The unburnt fuel enters the tailpipe and explodes when it comes in contact with the hot pipe. If I add more fuel won't it make the condition worse? I'll try it because it seemed to work with the stock exhaust, I just don't understand it. :)
I think you can get to a point where the air/fuel ratio is so lean that it can't be ignited by the spark plug, and when this mixture exits the cylinder it will accumulate in the exhaust until there is enough to ignite and cause the small backfire. Enriching the mixture could help here.
 

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Sojourner - I already have that column set to 10 because that worked well when I installed the Arlen Ness but still had stock pipes. I'll try raising it, but I'm confused. Pardon my ignorance, but I thought that backfiring in the tailpipe was caused by running rich. The unburnt fuel enters the tailpipe and explodes when it comes in contact with the hot pipe. If I add more fuel won't it make the condition worse? I'll try it because it seemed to work with the stock exhaust, I just don't understand it. :)
The increased fuel actually brings down the temperature of the exhaust gas so it's not lighting off when fresh oxygen comes in contact with it. Keep in mind a well tuned exhaust system will create a reverse pulse back up the pipe that hits the exhaust valve just as the valve opens. That pulse is suppose to help extract the spent charge and make more room for a fresh one. The side effect is that the reverse pulse is bringing up O2.
 

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Discussion Starter #13
The increased fuel actually brings down the temperature of the exhaust gas so it's not lighting off when fresh oxygen comes in contact with it. Keep in mind a well tuned exhaust system will create a reverse pulse back up the pipe that hits the exhaust valve just as the valve opens. That pulse is suppose to help extract the spent charge and make more room for a fresh one. The side effect is that the reverse pulse is bringing up O2.
Ah that makes sense.
 

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Discussion Starter #14
Thanks everyone for your help and for the maps. I'm going to give them a try today. I'll let you all know how it works out.

Again, thanks.
 

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Discussion Starter #15
Quick update.

First, thank you to everyone who helped me on this and those of you who sent maps.

I ended up using xcbullet's map (thanks again) and adding a little more fuel at the 0 and 2% throttle positions and its gotten rid of nearly all the backfire. Once in a while, usually after getting on it hard, it will still do it, but 95% of it is gone. I'm happy and am not so sure you can ever get rid of it 100% without spending a ton of money on cams or for someone to adjust the timing.

Happy Riding
 

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Quick update.

First, thank you to everyone who helped me on this and those of you who sent maps.

I ended up using xcbullet's map (thanks again) and adding a little more fuel at the 0 and 2% throttle positions and its gotten rid of nearly all the backfire. Once in a while, usually after getting on it hard, it will still do it, but 95% of it is gone. I'm happy and am not so sure you can ever get rid of it 100% without spending a ton of money on cams or for someone to adjust the timing.

Happy Riding
Yep, that's how it works. You proved it works when you said you still have some decel popping after you've gotten on it hard. Your top end is hotter as a result and the added fuel at 0 throttle isn't quite enough to cool it down to prevent the popping. Ride safe.
 
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