backfiring through exhaust under deceleration
- Thread starter rk97hd
- Start date
i checked the exhaust and both head pipes were loose. i tightened them and checked where the 2 headpipes went into the muffler, the connections there were tight. i then took it for a spin but it ran worse than ever - and i've owned it since it was new! does not idle, sputters, coughs, and if it was a horse, it would be shot to let it out of its misery! some have suggested an intake leak, how do i check for this? otherwise, a for-sale sign gets hung on it.
cdn-bigfoot
Junior Member
My bike started popping again and has gotten much worse on the last 2 rides.
I pulled on my pipes and whoa and behold.... wait for it!
The front pipe is loose in the exhaust flange again!
I had my Cobra pipe fixed by a welder friend after the pressed on collar came off and the pipe was no longer being held tight to the gasket by the flange. Well the welds must have broken. Pipe is loose again.
Popping, gargle and wap wap wap solved!
Back to the welder or replace the Cobra pipes?
I pulled on my pipes and whoa and behold.... wait for it!
The front pipe is loose in the exhaust flange again!
I had my Cobra pipe fixed by a welder friend after the pressed on collar came off and the pipe was no longer being held tight to the gasket by the flange. Well the welds must have broken. Pipe is loose again.
Popping, gargle and wap wap wap solved!
Back to the welder or replace the Cobra pipes?
Last edited:
Your choice, but you seem to have a recurring problem with these. Might be money ahead to replace.
As general advice on exhaust leaks, if your bike has the OEM exhaust pipes (not slip-ons, but the pipes themselves), they have a crossover to both sides of the bike and to both slip-ons. This would also apply to aftermarket pipes with crossovers. So both exhaust pipes would have to be covered to completely restrict the exhaust gases. However, in covering the exhausts we are trying to enhance any leak sounds so they can be heared more easily. The objective is not stalling the engine. Might not even be a good idea to do that.
Another way to find an exhaust leak is to just "shadow" the pipe with your hand being careful NOT to touch the pipe. If there is a leak (that are typically at the clamps), you should feel the "puffs" of the hot exhaust gases with your hand(s). This is NOT advisable at the heads though - too hot there. As I mentioned above, the one place to carefully inspect is the "y" right at the rear head where the pipe splits to head to both sides. We have seen cracks at that location.
TQ
cdn-bigfoot
Junior Member
My bike started popping again and has gotten much worse on the last 2 rides.
I pulled on my pipes and whoa and behold.... wait for it!
The front pipe is loose in the exhaust flange again!
I had my Cobra pipe fixed by a welder friend after the pressed on collar came off and the pipe was no longer being held tight to the gasket by the flange. Well the welds must have broken. Pipe is loose again.
Popping, gargle and wap wap wap solved!
Back to the welder or replace the Cobra pipes?
Just got my pipe back from my welder buddy. This time did "plug welds" by drilling 4 holes through the chrome ring and pipe. Then filled the holes with the weld.
Just have to re-install.
Love the look and sound of these pipes.
Just have to question the quality control and design of the Cobra pipes. I wouldn't recommend them!
Last edited:
whittlebeast
New Member
I am reposting this from a different forum. Hope this helps.
<<<<< snip >>>>>
Why does adding fuel in over-run change the backfiring?
The answer to this one is not what everyone has been led to believe. Hang with me on this one.
It takes three things to get backfiring in the exhaust. Heat and quite a bit of it, unburned fuel and air containing 02. Leave out any one of these things and the backfiring will not happen.
So how do each of these happen at the same time. The first one to address is unburned fuel in the exhaust. There is a couple of ways that this can happen. First is that for some reason, the the spark failed to light the compressed fuel and air in the combustion chamber. This can be either the spark plug failed to spark, the mixture was too lean to light or the mixture was too rich to light. All of these combinations will result in 02 and raw fuel ending up in the exhaust just waiting for an excuse to blow. The easiest way to get a source of heat is the next time the spark does manage to get the mixture to fire and when the exhaust valve does open a small bit of this following flame fights the mixture left over from the last miss hit and BANG you get a backfire out the exhaust. this is kinda rare but can happen.
The more likely thing is that the mixture was too rich and when the spark happened the fire ran out of fuel before it ran out of fuel and the left over fuel ended up in the exhaust just needing heat and a little o2 from somewhere. The place that is most common to find a little frest air is from the exhaust mannifold gasket that is leaking or from the joint between the head pipe and the muffler. At this point there is plenty heat floating around for the mixture to relight and BANG, you get a backfire.
The last possibility that I had not considdered was to fix this entire issue by flooding the motor in over-run with way too much fuel and and killing the heat in the exhaust and forcing the temps low enough to kill the possibility of a backfire. It turns out that there is apparently a 1ms minimum Pulse Width in the a Sporty code and in some situations this is still too much fuel to get all the way down to 14.7.
Remember that if the motor is at 14.7 or leaner in over-run there is just no fuel left in the exhaust and there is now way a backfire can happen. The problem is with the 1ms min PW you may never get down to 14.7
The way some of the Harley codes get around this is to kill fuel entirely in overrun. The problem with this solution is you can often feel the injectors suddenly turn back on at some point right before idle takes over or the throttle rolls back on. All fun and games of EFI tuning.
A big thanks to Steve at nightrider.com for helping pull all this together. The same guy that does the XIEDs.
Have fun tuning
AW
<<<<< snip >>>>>
Why does adding fuel in over-run change the backfiring?
The answer to this one is not what everyone has been led to believe. Hang with me on this one.
It takes three things to get backfiring in the exhaust. Heat and quite a bit of it, unburned fuel and air containing 02. Leave out any one of these things and the backfiring will not happen.
So how do each of these happen at the same time. The first one to address is unburned fuel in the exhaust. There is a couple of ways that this can happen. First is that for some reason, the the spark failed to light the compressed fuel and air in the combustion chamber. This can be either the spark plug failed to spark, the mixture was too lean to light or the mixture was too rich to light. All of these combinations will result in 02 and raw fuel ending up in the exhaust just waiting for an excuse to blow. The easiest way to get a source of heat is the next time the spark does manage to get the mixture to fire and when the exhaust valve does open a small bit of this following flame fights the mixture left over from the last miss hit and BANG you get a backfire out the exhaust. this is kinda rare but can happen.
The more likely thing is that the mixture was too rich and when the spark happened the fire ran out of fuel before it ran out of fuel and the left over fuel ended up in the exhaust just needing heat and a little o2 from somewhere. The place that is most common to find a little frest air is from the exhaust mannifold gasket that is leaking or from the joint between the head pipe and the muffler. At this point there is plenty heat floating around for the mixture to relight and BANG, you get a backfire.
The last possibility that I had not considdered was to fix this entire issue by flooding the motor in over-run with way too much fuel and and killing the heat in the exhaust and forcing the temps low enough to kill the possibility of a backfire. It turns out that there is apparently a 1ms minimum Pulse Width in the a Sporty code and in some situations this is still too much fuel to get all the way down to 14.7.
Remember that if the motor is at 14.7 or leaner in over-run there is just no fuel left in the exhaust and there is now way a backfire can happen. The problem is with the 1ms min PW you may never get down to 14.7
The way some of the Harley codes get around this is to kill fuel entirely in overrun. The problem with this solution is you can often feel the injectors suddenly turn back on at some point right before idle takes over or the throttle rolls back on. All fun and games of EFI tuning.
A big thanks to Steve at nightrider.com for helping pull all this together. The same guy that does the XIEDs.
Have fun tuning
AW
tlyoungb
Junior Member
I watched a video from that nightrider.com website. It was talking about adding O2 sensors. O2 sensors are just to Cal. bikes right?