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My bike had started to run REALLY rough lately, and developed a big wide flat spot above 5k rpm. It's an 06' with ~8700 miles, and has had regular maintenance. The only thing I've touched recently was the air filter, replacing the stock with a K&N.

Basically, the usual thump-thump turned into a thud-thud, and acceleration above 5K was nearly non-existent.

I ran some carb cleaner through a tank of gas (lazy), and gave it a good week or so of running to blast out the cobwebs, and I think it's getting better.... but I'm not sure.

Has anyone seen their EX go a little flat and run rough after down time?
 

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you do the normal pilot jet adjustment?
Been a long time since I've seen one of those posts but FOG doesn't mind repeating himself for the millionth time if he's still around.
 

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stringsofsuture said:
you do the normal pilot jet adjustment?
Been a long time since I've seen one of those posts but FOG doesn't mind repeating himself for the millionth time if he's still around.
No... I didn't really know it was needed. I'm familliar with the airbox mod, not the jet adjustment?
 

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Your addition of the KN filter has altered the carb mixture.


I would suggest two things to check.
Remove and clean it insides of the spark plug boots.
Un plug and adjust the pilot screws to 2.5 turns out.
These are standard thing that need to be done to even new bikes.
Your addition of the KN filter has altered the carb mixture.

FOG
 

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Administrator said:
My bike had started to run REALLY rough lately, and developed a big wide flat spot above 5k rpm. It's an 06' with ~8700 miles, and has had regular maintenance. The only thing I've touched recently was the air filter, replacing the stock with a K&N.

Basically, the usual thump-thump turned into a thud-thud, and acceleration above 5K was nearly non-existent.

I ran some carb cleaner through a tank of gas (lazy), and gave it a good week or so of running to blast out the cobwebs, and I think it's getting better.... but I'm not sure.

Has anyone seen their EX go a little flat and run rough after down time?
This definitely sounds like an air/fuel mix problem. If you're replacing with K&N's recommended air filter replacement, it shouldn't require a needle adjustment, but at 8700 miles, it wouldn't hurt to do one anyway. Some things you may want to double check:
  • Is the air filter on securely?
  • Are the seals around the air box in place properly? Sometimes you can get a gap that lets extra air in at the mount point and that won't rear it's head until certain rpm ranges.
Check the areas circled for gaps or loose connections/seals:


These would be the easy fixes that may not require you to do a carb-rejetting... don't rule the rejetting out, though.

I second Strings' suggestion that we hope FOG posts a response to this. :)

--Monkey

EDIT: Looks like I spoke too soon. FOG beat me to it. Heh.
 

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K&N Filters just aren't worth it on any machine you might own. They don't do jack, jack.

But while you're down there, install/splice a small engine fuel filter between the tank and the carbs.
 

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Well, in an act of desperation, I recently just picked up a UNI filter from my local cycle shop, as I was suspecting the filter. After putting it in, that's when I saw the bit of improvement I mentioned. I had just given in and brought it to my dealership for a 7500-mile service and to let them know that it was running rough and lacking power, but when I called two days later to find out where my bike was, the tech got on the phone and said that he didn't see anything wrong at all, and that that's how they all ran. My last visit to the dealership...

Anyhow, so the K&N really does lean it out that much?
 

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EX500's are notorious for being jetted lean around there from the factory. I had to tune mine myself to fix that. you'll have to turn the pilot jet screws out a little bit to see if it improves it any with the stock filter.
 
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i had to adjust my ex's pilot screws in stock form, since my bike surged and had the flat spot even when brand new. 2.5 turns out worked for me...

even after putting my muzzy on the bike runs great
 

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pretty sure iv heard people say that our bikes get a flat spot around 5k due to jetting. solution? crank her up to a higher rpm ;D
 

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Ahh the good ol' flat spot at 4-6k. Well its been said but i like to reitterate. Basicaly you tampered with the air flow which needs to be corrected by adjusting the pilot screws. These pilot screws are located on the bottom side of the carberators. They come sealed from the factory, so you have to get the metal plug out and the tighten the screws down till they make contact, STOP then turn them back out 2.5 turns each. This should correct your problem, unless your carbs are dirty, and need to be cleaned :)

Janinja
 

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Well pilots my help up to 4000 RPMs, the pilot jets are only for idle and low rpm cruise if your problem is above that then pilots aren't the answer heres some helpful info from the Boys at Factory Pro, their web server is down at this moment, but Vmax outlaw website has it posted here http://vmaxoutlaw.com/tech/cv_carb_tuning.htm. This should help you with your problem and allow you to jet and pod your bike in the future if you like, I know I know "don't take off the airbox you'll be sorry" Horse Hockey! The airbox is 5 pounds of useless crap! Properly jet the bike and happiness is yours, says I!
 

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I have pods on the my sons ex250 after hearing all the don't do it stuff on the 250 board, bike runs better than ever and was good for [email protected] in the 1/8 mile maybe better but we ran out of season, we just got two 500s one going to be my sons street bike and the other will be his drag bike, pods and jet kit and exhaust are on the way for the street bike and the drag bike will have 36mm slingshots carbs from a GSXR 1100. I'm on the hunt for a torn up after market exhaust for the drag bike don't much care what it looks like! Also going to advance timing 5 degrees on both.
 
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