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Discussion Starter #1
I just bought a used 2012 Kawi Vulcan 900 Classic SE last month, had about 5500 miles and in great condition. The original owner installed cobra straight pipes, a Cobra Fi2000R, and a Barons BAK. Idle seemed very low but stable. When I first started riding it, no backfiring. After doing some upgrades/mods (see list below), lots of backfiring/popping on deceleration. Since it did not backfire before my mods, and I have no touched the exhaust, I don't think its an exhaust leak. I did remove the BAK so I could paint the plate, but I am 99.9% sure I reinstalled it correctly. When my wife rides on the back (she is about 100lbs), it backfires much worse. Sounds like a retarded machine gun in my neighborhood. Going down hills is much worse. I need some ideas on what I can check to get it to stop backfiring. Since I am new to this bike I need newbie instructions, with pictures and stuff (would help a lot).

So far, I put about 3/4 bottle of seafoam in the gas tank (its still mostly full), and I increased the idle rpms (no tach so I guesstimated 1000rpms).

Barons SS line kit
Kuryakyn Dual USB port
Chrome Brake & clutch controls
LED headlight bulb (modified for correct beam pattern)
LED Taillight & license Plate bulb
LED turn signals (switchbacks)
Instrument Panel LEDs
LED diode kit
Electronic flasher relay
Rest of the mods are cosmetic only
 

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Seafoam should be added at the rate of 1 ounce per gallon.If you added 3/4 of a 16 ounce can of Seafoam to your gas tank you have way too much in there.Sorry I can't be more help on the backfiring issue.
 

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Besides the seafoam deal, I think you probably need to tune your fuel processor. I went with the Cobra autotune processor to avoid this issue. Also recommend running 87 octane grade fuel. Maybe drain the fuel from tank and start with fresh tank?
 

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......... When my wife rides on the back (she is about 100lbs), it backfires much worse...........

Is it possible that when your wife is riding (even though she is obviously small in stature) thats just enough added weight to cause something in the exhaust to tweak/flex and leak? Probably not even close but just a thought.
 

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It is not backfiring for one thing, it is simply closed throttle decel popping in the exhaust. Modern bikes do not backfire. To prove it is decel popping simply pull in the clutch and the popping immediately stops. All modern bikes pop on decel because the emissions restrictions require very lean fuel/air mix on closed throttle. Anytime you mod the exhaust it makes the popping worse because more open exhaust (especially straight through exhaust) does not dampen the popping and most often it further leans out the fuel/air mix, making the popping even worse. Even opening up the intake can increase decel popping. Changing the idle does nothing, never will. Fuel grade makes no difference either. Same for Seafoam or any kind of fuel cleaner, because that is not the issue. Your bike simply needs more fuel on closed throttle/decel conditions.

If you want to keep the modded exhaust the only two options are; 1. pull in the clutch, this keeps the bike momentum from "pushing" the engine to breathe more than the closed throttle allows, or 2. Install some type of fuel management system that allows you to richen up the fuel/air ratio. Doing this stop the popping but it will also decrease your fuel mileage.

Your wife's weight on the bike does nothing to the exhaust. It pops more with your wife on the back because during decel, with her added weight on the bike there is even more momentum on decel and the bike/load combo is pushing the engine on decel even more. Again, pull in the clutch and the popping stops. Dont call it backfiring, its just popping. Call Cobra and they "might" help, but may not be able to, because they cannot legally direct you to modify the fuel/air mix because it alters the emissions. If Cobra does not help, find a cycle shop with an exhaust gas analyzer and a dyno and have them set the fuel/air mix control on the Cobra Fi2000 as much as they can to richen up the fuel enough to reduce the popping.
 

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Discussion Starter #7
Thanks for the replies, I am going to check out the Cobra Fi2000R first to see if there are any modifications I can make, then try Cobra customer service to see if they can help. andyvh1959 your right it stops immediately when I pull in the clutch, so I will refrain from calling it backfiring. I did some more digging and found reference to a "marble" mod that blocks air flow to the exhaust (an emissions control thing). If the Cobra fuel module and Cobra customer service does not work, I will try that next. Great advice guys, thanks.
 

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Discussion Starter #8
This is my first cruiser style bike, I started on crotch rockets so I use 92 octane (+/- 1). Am I supposed to be using a different octane? I was under the impression that using a lower than recommended Octane rating can cause issues with performance, but using a higher than recommended octane rating only causes issues with your wallet.
 

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This is my first cruiser style bike, I started on crotch rockets so I use 92 octane (+/- 1). Am I supposed to be using a different octane? I was under the impression that using a lower than recommended Octane rating can cause issues with performance, but using a higher than recommended octane rating only causes issues with your wallet.
Premium gas will make the popping louder as it burns slower and is igniting in your exhaust. The manual on the 900 calls for 87. That's all I've ever used. Also, if your fuel processor can be adjusted add a small amount of fuel in 0-5% range. That along with 87 octane will likely cure this.
 

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It is not backfiring for one thing, it is simply closed throttle decel popping in the exhaust. Modern bikes do not backfire. To prove it is decel popping simply pull in the clutch and the popping immediately stops. All modern bikes pop on decel because the emissions restrictions require very lean fuel/air mix on closed throttle. Anytime you mod the exhaust it makes the popping worse because more open exhaust (especially straight through exhaust) does not dampen the popping and most often it further leans out the fuel/air mix, making the popping even worse. Even opening up the intake can increase decel popping. Changing the idle does nothing, never will. Fuel grade makes no difference either. Same for Seafoam or any kind of fuel cleaner, because that is not the issue. Your bike simply needs more fuel on closed throttle/decel conditions.

If you want to keep the modded exhaust the only two options are; 1. pull in the clutch, this keeps the bike momentum from "pushing" the engine to breathe more than the closed throttle allows, or 2. Install some type of fuel management system that allows you to richen up the fuel/air ratio. Doing this stop the popping but it will also decrease your fuel mileage.

Your wife's weight on the bike does nothing to the exhaust. It pops more with your wife on the back because during decel, with her added weight on the bike there is even more momentum on decel and the bike/load combo is pushing the engine on decel even more. Again, pull in the clutch and the popping stops. Dont call it backfiring, its just popping. Call Cobra and they "might" help, but may not be able to, because they cannot legally direct you to modify the fuel/air mix because it alters the emissions. If Cobra does not help, find a cycle shop with an exhaust gas analyzer and a dyno and have them set the fuel/air mix control on the Cobra Fi2000 as much as they can to richen up the fuel enough to reduce the popping.
+1 on that i noticed the same when i installed my exhaust, just pull in the clutch. Problem solved
 

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Just to set it straight, I not putting anyone down for calling it backfiring, or that someone wants their bike to stop popping. Its just ones of those things that irked me when I worked at a dealership and riders would complain their bike was backfiring. I have even heard mechanics incorrectly refer to it as backfiring, which if they really described it properly they'd realize there is very little chance it really is backfiring.

Back in the days of simple fuel systems and points ignition, backfiring was possible. I recall engines "burping" back out the carb because the timing was way off or the valves weren't sealing. But modern engines simply do not backfire, but a lot of them pop a lot on decel.

Think of decel popping this way: you are running down a hill, gravity is pushing you faster and faster but your breathing can't keep up, you want to go slower but you can't because you are being pushed downhill, can't catch your breath. Kinda similar for a cycle engine on decel. The mass and momentum of the bike on decel now has the rear tire "driving" the engine forward at closed throttle. As the engine is pushed forward by the bike, it cannot breathe in enough fuel/air to support combustion on every stroke of the engine. As the bike is pushed along and the engine keeps pumping eventually enough fuel and air is sucked in to burn when the spark plug fires. Because most bikes provide a spark twice during a complete intake-compression-power-exhaust cycle, the engine can fire the plug when the exhaust valve is open, and if there is enough fuel/air has gotten in, it makes the "POP" out the exhaust.

Kind of like a Jake Brake on trucks, the engine acts as a brake but it is still pumping/breathing as the truck rolls along. Difference is during Jake Brake operation the exhaust valves are just cracked open to offer some resistance/engine braking.
 

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Just to set it straight, I not putting anyone down for calling it backfiring, or that someone wants their bike to stop popping. Its just ones of those things that irked me when I worked at a dealership and riders would complain their bike was backfiring. I have even heard mechanics incorrectly refer to it as backfiring, which if they really described it properly they'd realize there is very little chance it really is backfiring.

Back in the days of simple fuel systems and points ignition, backfiring was possible. I recall engines "burping" back out the carb because the timing was way off or the valves weren't sealing. But modern engines simply do not backfire, but a lot of them pop a lot on decel.

Think of decel popping this way: you are running down a hill, gravity is pushing you faster and faster but your breathing can't keep up, you want to go slower but you can't because you are being pushed downhill, can't catch your breath. Kinda similar for a cycle engine on decel. The mass and momentum of the bike on decel now has the rear tire "driving" the engine forward at closed throttle. As the engine is pushed forward by the bike, it cannot breathe in enough fuel/air to support combustion on every stroke of the engine. As the bike is pushed along and the engine keeps pumping eventually enough fuel and air is sucked in to burn when the spark plug fires. Because most bikes provide a spark twice during a complete intake-compression-power-exhaust cycle, the engine can fire the plug when the exhaust valve is open, and if there is enough fuel/air has gotten in, it makes the "POP" out the exhaust.

Kind of like a Jake Brake on trucks, the engine acts as a brake but it is still pumping/breathing as the truck rolls along. Difference is during Jake Brake operation the exhaust valves are just cracked open to offer some resistance/engine braking.
Very well writen..
:grin2:
 

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andyvh1959, that is the best explained reasoning as to why our bikes pop on decel. I too have the decel pop, but have never taken the logic to pull the clutch. I feel I'd rather not use this as a remedy as I think your brakes would get worn significantly quicker. not to mention, more chance of danger. My popping is minor to me and so no big deal.

I have done all of the mods (see below) and tuning the Cobra FI2000R has been the most significant improvement/reduction, but still not illuminated all.

As for octane, I'm at sea level with high humidity, mine seems to run best in mid-grade, only seat of the pants observation.

If the octane rating is higher (91/93), wouldn't that mean more flammable gas and thus burning quicker not slower?

Take the time to do research on here and tune your Cobra FI module, most all of us have tweaked it. Rarely is it to the factory recommended specs, again COBRA will not tell you to tune it rich for the sake of minimizing decal pop.

To prove it to myself that I had the FI2000R pretty close to optimum settings, I pulled my plugs, A nice light coffee color. It still pops a little, no big deal to me, keeps the other drivers attention on where I am on the road.

Good luck!
 

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Thanks for the tip, I will switch back to 87 octane and see about adjusting the fuel processor.
The marble mod, has done the best for reducing the poping on de-acceleration for me. I still get some if the throttle is just opened a little then closed on a fair down hill grade. I can live with it. Cost time and $.02 ( used a wire nut & tape)
 

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andyvh1959, that is the best explained reasoning as to why our bikes pop on decel. I too have the decel pop, but have never taken the logic to pull the clutch. I feel I'd rather not use this as a remedy as I think your brakes would get worn significantly quicker. not to mention, more chance of danger. My popping is minor to me and so no big deal.

I have done all of the mods (see below) and tuning the Cobra FI2000R has been the most significant improvement/reduction, but still not illuminated all.

As for octane, I'm at sea level with high humidity, mine seems to run best in mid-grade, only seat of the pants observation.

If the octane rating is higher (91/93), wouldn't that mean more flammable gas and thus burning quicker not slower?

Take the time to do research on here and tune your Cobra FI module, most all of us have tweaked it. Rarely is it to the factory recommended specs, again COBRA will not tell you to tune it rich for the sake of minimizing decal pop.

To prove it to myself that I had the FI2000R pretty close to optimum settings, I pulled my plugs, A nice light coffee color. It still pops a little, no big deal to me, keeps the other drivers attention on where I am on the road.

Good luck!
The higher the octane the slower burning. Lead was used as cheap/stable way to increase the octane. Aviation piston engines still use 100LL fuel. EPA is trying to get rid of 100LL, stability is a problem with unleaded fuel. Big engines of WWII used 115/145 octane.

Ken
 

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Rustydog is right, higher Octane fuels are intended to burn slower, which is a way to control detonation (pinging). Detonation occurs when incomplete fuel burning in the combustion chamber self ignites without the spark plug. The "ping" is actually a small explosion in the combustion chamber which can be very harmful to the engine. Detonation can occur when air cooled engines get too hot and the fuel can self ignite when enough air gets in with the fuel. Many people think higher octane fuels give better gas mileage, which it "might" if the detonation is significant. But really, using the lowest octane fuel your bike can run without pinging is the better choice. A fuel injected engine can adjust for lower octane values if the engine control systems monitor pinging. Also, some riders think using higher octane fuel reduces the popping in the exhaust, which it cannot because the issue is a lean fuel/air mix and has nothing to do with octane level. Fuel additives also have no impact on exhaust popping on closed throttle decel.

On my BMW R1100RS I installed a Techlusion fuel adjustment system after I modified the muffler with my own baffle design. With the Techlusion I can slightly alter the fuel/air mix at various throttle positions. When I adjust the fuel to air ratio at idle and slight throttle open positions I can almost delete all exhaust popping entirely. But in doing that my fuel mileage drops 10% to 15%. So I dialed the fuel/air mix back to stock and the popping returned. After that experience it was pretty evident the issue is exhaust popping (not backfiring) caused by a lean fuel/air mix on decel closed throttle conditions.
 
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