Excessive pop on decel
Most backfires through the exhaust on decelerating in gear, is due to an exhaust leak. What happens is, air that is sucked in from the leak during deceleration, mixes with the unburnt fuel exiting the cylinder, and fires when it reaches the minimum air/fuel ratio, causing the backfire. Check your exhaust gaskets, mating surfaces (between pipes and/or mufflers) and search for holes. In many cases, when you fix the leak, the backfire will go away.
Road Master
Joined: Jul 2008
Posts: 1,021
Likes: 2
Could be either. Tune can mask a physical problem as well.
Last edited by jstreet0204; Jul 21, 2010 at 09:18 AM.
Intermediate
Joined: Jul 2010
Posts: 44
Likes: 0
808WES,
Seems like you are saying that reducing the backpressure by changing the exhaust is not a contributing factor when backfiring occurs!
Is that correct or is the change in backpressure also a culprit that is independent of leaks?
The reason I ask is beacuse my bike had no backfiring before I changed the exhaust backpressure (By drilling a bypass in the baffles). No other changes took place between when it did not backfire and now that it does!
Bob Nisbet
Seems like you are saying that reducing the backpressure by changing the exhaust is not a contributing factor when backfiring occurs!
Is that correct or is the change in backpressure also a culprit that is independent of leaks?
The reason I ask is beacuse my bike had no backfiring before I changed the exhaust backpressure (By drilling a bypass in the baffles). No other changes took place between when it did not backfire and now that it does!
Bob Nisbet
Intermediate
Joined: Mar 2010
Posts: 36
Likes: 0
I had really bad pop with my Thunderheader 2-into-1 (Mo-Flow Low-Restriction Intake) on a used 2006 Heritage, 88B engine. Everybody I have talked to with this exhaust has issues with deceleration backfire and popping.
I have a Power Commander III USB (came with the used bike), so I downloaded the software, jacked into the PowerCommander via the USB, checked the map (correct one loaded - for ThunderHeader 2-1 and Screamin' Eagle intake) and then I put "16" into the first column (Throttle = 0 at all RPM). This got rid of 95% of the pop on decel. I decided to also add "16" to the entire second column (2% throttle at all RPM) and that got rid of some more of it.
The biggest difference was setting the "Throttle Zero". I did it with the engine running (I don't have the 9V battery widget) and just wrapped the throttle up all the way to get the top throttle. When I later hooked up a battery and set the throttle with the engine off, I got a better reading and a very marked improvement in all RPM, all throttle conditions.
I think that the throttle zero is a big thing that people with PC III don't worry about - just buy the thing, put in the map and attach it to the bike. Without zeroing the throttle correctly, you will constantly be operating in the wrong place on the map. Read the instructions thoroughly, though, or you won't set the 'zero-throttle' number correctly.
I strongly suggest setting the throttle zero without the bike running, for more accurate results. You WILL have to have a 9V battery hooked to the Power Commander, though. If anybody needs to jury-rig the 9V battery thing, because you don't have the gizmo that came with the Power Commander, leave a message here and I will show you how I rigged it.
I have a Power Commander III USB (came with the used bike), so I downloaded the software, jacked into the PowerCommander via the USB, checked the map (correct one loaded - for ThunderHeader 2-1 and Screamin' Eagle intake) and then I put "16" into the first column (Throttle = 0 at all RPM). This got rid of 95% of the pop on decel. I decided to also add "16" to the entire second column (2% throttle at all RPM) and that got rid of some more of it.
The biggest difference was setting the "Throttle Zero". I did it with the engine running (I don't have the 9V battery widget) and just wrapped the throttle up all the way to get the top throttle. When I later hooked up a battery and set the throttle with the engine off, I got a better reading and a very marked improvement in all RPM, all throttle conditions.
I think that the throttle zero is a big thing that people with PC III don't worry about - just buy the thing, put in the map and attach it to the bike. Without zeroing the throttle correctly, you will constantly be operating in the wrong place on the map. Read the instructions thoroughly, though, or you won't set the 'zero-throttle' number correctly.
I strongly suggest setting the throttle zero without the bike running, for more accurate results. You WILL have to have a 9V battery hooked to the Power Commander, though. If anybody needs to jury-rig the 9V battery thing, because you don't have the gizmo that came with the Power Commander, leave a message here and I will show you how I rigged it.
Banned
Joined: Oct 2007
Posts: 1,494
Likes: 5
I had really bad pop with my Thunderheader 2-into-1 (Mo-Flow Low-Restriction Intake) on a used 2006 Heritage, 88B engine. Everybody I have talked to with this exhaust has issues with deceleration backfire and popping.
I have a Power Commander III USB (came with the used bike), so I downloaded the software, jacked into the PowerCommander via the USB, checked the map (correct one loaded - for ThunderHeader 2-1 and Screamin' Eagle intake) and then I put "16" into the first column (Throttle = 0 at all RPM). This got rid of 95% of the pop on decel. I decided to also add "16" to the entire second column (2% throttle at all RPM) and that got rid of some more of it.
The biggest difference was setting the "Throttle Zero". I did it with the engine running (I don't have the 9V battery widget) and just wrapped the throttle up all the way to get the top throttle. When I later hooked up a battery and set the throttle with the engine off, I got a better reading and a very marked improvement in all RPM, all throttle conditions.
I think that the throttle zero is a big thing that people with PC III don't worry about - just buy the thing, put in the map and attach it to the bike. Without zeroing the throttle correctly, you will constantly be operating in the wrong place on the map. Read the instructions thoroughly, though, or you won't set the 'zero-throttle' number correctly.
I strongly suggest setting the throttle zero without the bike running, for more accurate results. You WILL have to have a 9V battery hooked to the Power Commander, though. If anybody needs to jury-rig the 9V battery thing, because you don't have the gizmo that came with the Power Commander, leave a message here and I will show you how I rigged it.
I have a Power Commander III USB (came with the used bike), so I downloaded the software, jacked into the PowerCommander via the USB, checked the map (correct one loaded - for ThunderHeader 2-1 and Screamin' Eagle intake) and then I put "16" into the first column (Throttle = 0 at all RPM). This got rid of 95% of the pop on decel. I decided to also add "16" to the entire second column (2% throttle at all RPM) and that got rid of some more of it.
The biggest difference was setting the "Throttle Zero". I did it with the engine running (I don't have the 9V battery widget) and just wrapped the throttle up all the way to get the top throttle. When I later hooked up a battery and set the throttle with the engine off, I got a better reading and a very marked improvement in all RPM, all throttle conditions.
I think that the throttle zero is a big thing that people with PC III don't worry about - just buy the thing, put in the map and attach it to the bike. Without zeroing the throttle correctly, you will constantly be operating in the wrong place on the map. Read the instructions thoroughly, though, or you won't set the 'zero-throttle' number correctly.
I strongly suggest setting the throttle zero without the bike running, for more accurate results. You WILL have to have a 9V battery hooked to the Power Commander, though. If anybody needs to jury-rig the 9V battery thing, because you don't have the gizmo that came with the Power Commander, leave a message here and I will show you how I rigged it.
Thread
Thread Starter
Forum
Replies
Last Post
TickTock
Ignition/Tuner/ECM/Fuel Injection
16
Jun 18, 2007 10:52 PM
