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Hi there all

I have a 2013 Fat Bob and recently replaced the original air filter with a screaming eagle heavy breather, Is it my imagination or is my fuel consumption now worse than ever?

Do you have to tune the bike after replacing the filter?

Thanks

Wynand
 

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Normally you do the breather coupled with an exhaust and a tune...the breather and exhaust drastically affect your air/fuel mixture so you end up getting a new tune programmed for your particular exhaust/breather.
 

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Your bike has O2 sensors. Those sensors control the air/fuel mixture. Since you are taking more air in, the bike needs more fuel to match. So, yes, you are probably burning more fuel.

I am surprised it is that significant though. With everything else being stock, I wouldn't have guessed to be more than a 5-10% difference.

Were you expecting it to improve fuel economy?
 

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Mississippi Cajun
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Your bike has O2 sensors. Those sensors control the air/fuel mixture. Since you are taking more air in, the bike needs more fuel to match. So, yes, you are probably burning more fuel.

I am surprised it is that significant though. With everything else being stock, I wouldn't have guessed to be more than a 5-10% difference.

Were you expecting it to improve fuel economy?
OK, while I totally agree with the O2 sensor, fuel/air mix thingee that you just stated, I have one here that sort of contradicts: my fuel mileage started to really suck last few trips. I had a very dirty stage 1 air filter that I couldn't soak clean and ordered a new one....which I had to wait for since they were out of stock. Got some of the HD de-greaser/cleaner and hosed the filter (got all sorts of funk out of it). Next tank of gas, mileage was up 3mpg. Next one was up 4. More air, better economy would SEEM to contradict the mixture idea. Better breathing, more efficiency?
 

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Call me Gig.
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I just added a heavy breather and Stage 1 flash last week and I'm think I'm seeing worst mileage. But I'm not going to blame the bike. It seems to breath so much easier than it did before that I'm running much higher RPMS and staying in gears lower gears longer for the performance increase.

On my little 25 mile highway run to my favorite weekend watering hole I noticed that I'm staying in 5th on the highway where I used to be in 6th.

I assume the new will wear off at some point and I'll get back into using the higher gears.
 

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OK, while I totally agree with the O2 sensor, fuel/air mix thingee that you just stated, I have one here that sort of contradicts: my fuel mileage started to really suck last few trips. I had a very dirty stage 1 air filter that I couldn't soak clean and ordered a new one....which I had to wait for since they were out of stock. Got some of the HD de-greaser/cleaner and hosed the filter (got all sorts of funk out of it). Next tank of gas, mileage was up 3mpg. Next one was up 4. More air, better economy would SEEM to contradict the mixture idea. Better breathing, more efficiency?
At some point, the "very dirty" filter is going to affect performance to the extent that you are forcing it to work harder just to suck air into the motor. In a naturally aspirated engine, a high-flow air filter doesn't force more air into a motor, it simply restricts the engine's ability to "suck" air less. That's why they run like crap or not at all when you take the filter completely off. They are sucking too much air.

The motor has to have a given amount of air and fuel to run, so when you are overly restricted, you have to work the motor harder to get it to suck enough air to run the way you want it to.

Both of my H-Ds lost fuel economy when I did the exhaust/AC/Power Commander mod. It's hardly noticeable at highway cruise and as much as 10-15% when you are cranking hard on it around town.
 

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I've got the Screamin' Eagle Pro Stage IV Race Kit installed in my new 103 Street Bob. (three weeks old this past Friday). It has 916 miles on it and I'm getting around 41/42 mpg. (93 octane / with REAL gas).....I don't really have anything to compare to but I don't think that's too bad, then again, I haven't been running it real hard yet.

It IS rather 'cold hearted' though. If it sits for more than two days, it takes longer to warm up/run smooth. Characteristic of the motor.
 

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Mississippi Cajun
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OK, Chas, that makes sense. Tnx.
 

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More air, better economy would SEEM to contradict the mixture idea. Better breathing, more efficiency?
What happens is, yes you do get more air and thus more fuel as well to mix with it at a specific throttle position...


But what happens is you do not need to open the throttle as much to get the needed air/fuel mixture into the motor to go a specific speed.


I only need to open the throttle on my bike 1/8 to 1/4 to cruise 75 MPH where on a stock bike someone would have to open the throttle higher to cruise at the same speed..... and I'm STILL getting 40 MPG on a carbed bike!
 
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