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Discussion Starter #1
Hey Guys,

Just checking to see if anyone can tell me if I fuel management system (power commander or similar) is needed when using the K&N filter with an aftermarket exhaust.

Thanks,
Vinny
 

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Mine was running lean just putting the cobra swept exhaust with the stock air filter. I know they say you don't need a controller with just an exhaust, but I tend to think that you do, based on my experience.
 

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Several people have commented that they are running either aftermarket or de-baffled exhaust with the K&N stock filter replacement and not having issues with the motor being lean. A large part of the air restriction is the path it takes into the air box. It has been described as a crooked straw. The air literally has to be sucked between the heat radiating fins of the rear jug to get into the air box. I am sure the K&N will give better flow than a stock filter in a head to head test. But when the restiction is upstream of the filter, I don't see how it can make much of a difference.
 

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In my experience, most bikes run a little to a lot lean from the factory due to emission Requirements. Especially Metric since they have to pay tariffs and get scrutinized so much being brought over. Opening up the exhaust allows the exhaust gases to be removed quicker and more efficiently, which can cause the engine to run a little bit more lean. Adding an Aftermarket air filter that flows a LOT (usually) more air than stock-further leans the air fuel mixture. I will not add an aftermarket air filter, or alter my stock airbox in any way until I can install a fuel controller of some sort. The optimal air fuel ratio is 14.6:1, I believe. The cylinders get cooled by the incoming fuel. If you make the fire hotter... Everything gets hotter... Oil, Cylinders, water.... You can do whatever you want on your bike, But I promise you that every race car, truck, bike, boat out there - has bigger jets (more fuel/ fuel controller) for their upgraded exhaust and intake.
 

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Discussion Starter #5
Mine was running lean just putting the cobra swept exhaust with the stock air filter. I know they say you don't need a controller with just an exhaust, but I tend to think that you do, based on my experience.
What were the indicators that it was running lean (sorry if that is a dumb question)?

Jeep Pirate said:
Several people have commented that they are running either aftermarket or de-baffled exhaust with the K&N stock filter replacement and not having issues with the motor being lean. A large part of the air restriction is the path it takes into the air box. It has been described as a crooked straw. The air literally has to be sucked between the heat radiating fins of the rear jug to get into the air box. I am sure the K&N will give better flow than a stock filter in a head to head test. But when the restiction is upstream of the filter, I don't see how it can make much of a difference.
I read those posts too... I am just worried about damaging my 9. I do WANT to agree with the logic.
 

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Discussion Starter #6
In my experience, most bikes run a little to a lot lean from the factory due to emission Requirements. Especially Metric since they have to pay tariffs and get scrutinzed so much being brought over. Opening up the exhaust allows the exhaust gases to be removed quicker and more efficiently, which can cause the engine to run a little but more lean. Adding an Aftermarket air filter that flows a LOT (usually) more air than stock-further leans the air fuel mixture.. I will not add an aftermarket air filter, or alter my stock airbox in any way until I can install a fuel controller of some sort. The optimal air fuel ratio is 14.6:1 i believe. The cylinders get cooled by the incoming fuel. If you make the fire hotter... Everything gets hotter... Oil, Cylinders, water.... You can do whatever you want on your bike, But I promise you that every race car, truck, bike, boat out there - has bigger jets (more fuel/ fuel controller) for their upgraded exhaust and intake.
Thanks for the post, good points.
 

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What were the indicators that it was running lean (sorry if that is a dumb question)?


A regularly burning plug should be tan to a light grey color after a good run. Too light is almost always an indicator of a lean fuel condition. A rich bike would have a sooty deposit all over the plug. But our bikes are usually running lean, so the Richness issue isnt seen very often unless some serious modifications have been made.
 

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I have an 07 900 vulcan with vance and hines slash cut staggered, with baffles and hard kore baffles. I'm running a stock intake and thinking of getting a k&n filter. I haven't pulled my plugs to see how the bike is running (lean or not), but one thing I have noticed is the smell of fuel coming out the pipes at idle and can catch a sniff of the same on the highway when the crosswind is just right.

Does the smell of fuel mean that I'm running a bit rich or should I be looking at the plugs to make sure?
 

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After about a 10 minute drive, my front pipe turned gold/blue right at the engine, indicating that the pipe was too hot, and the bike was backfiring on decel. Luckily just the pipe underneath the heat shield discolored, and not the actual shield.
 
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