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Old August 16th, 2019, 11:24 PM   #1
nocturncal
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Bike Runs Better with CICMOD Air Filter vs K&N

I been troubleshooting a hesitation around 9k with the throttle wide open, and finally solved it! Some questions though...

I just took out a CICMOD Air filter that I bought from Amazon a year ago, and cleaned and reoiled and put in a K&N filter that came with my bike when I bought it from the previous owner (when I bought the bike 10 years ago, I didn't know it had a reusable air filter and bought another air filter off of amazon, and decided to just use the Amazon one).

After the K&N was put in, I started having a hesitation with the bike when WOT at 9k where it would stop accelerating unless I backed off the throttle. I took the K&N filter out, cleaned the CICMOD Air filter, and put that back in. It solved the hesitation issue!

Im trying to understand why is this. The K&N filter seemed loose inside the air box, vs the CICMOD which fit very snug in the air box. I had roughly 6mm of play on both sides of the filter. Could it be the K&N filter was loose, casing air to get past the filter and cause the bike to run lean?

Reading the 250 manual in the section about air cleaner element cleaning, it talks about plastic holders that go between the stock air filter. My bike never had these plastic holders. Is the holder needed on aftermarket filters like the K&N?
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Old August 17th, 2019, 12:02 AM   #2
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No need for plastic filter holders as that's 3-piece assembly with foam filter in factory configuration.

K & N is 1-piece that's same size as factory combo, if you have air-gap on any edge, it's not correct filter version (might be for some other bike). My K & N fits snugly all around.

Too many variables to say lean or rich. You'd need to test by adjusting only thing. Such as AFR while keeping same filter in place:

1. Filter-X: add shim to slide needle to richen mid-range, does it make stumbling better or worse? If better, then it was lean. If doesn't change or made worse, then it was rich.

2. Filter-Y: add shim to slide needle to richen mid-range, does it make stumbling better or worse? If better, then it was lean. If doesn't change or made worse, then it was rich.

Now you've got cartesian-product of 2x2 variables for 4 possible combinations. Test all 4 and write down results. Then we'd have enough data to draw conclusion.
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Old August 17th, 2019, 05:13 AM   #3
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The are easier ways to make it a little richer at the stumbling point for test purposes than shimming the needles. Also safer for the diaphragms. One is to use the starter lever. Another is to temporarily put some tape across the filter or filter box inlet to block a little air flow.
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Old August 17th, 2019, 03:54 PM   #4
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Thanks for the replies. I will try the tape around the filter to block some flow method. I don't want to dedicate to much time to this as the bike runs fine with the CICMOD filter and just trying to satisfy my curiosity.
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Old August 17th, 2019, 11:52 PM   #5
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Quote:
Originally Posted by Triple Jim View Post
The are easier ways to make it a little richer at the stumbling point for test purposes than shimming the needles. Also safer for the diaphragms. One is to use the starter lever. Another is to temporarily put some tape across the filter or filter box inlet to block a little air flow.
Thing is, choke is fixed amount of fuel. The higher and higher engine revs, especially under load, the less this additional fuel contributes to overall AFR.

It's not a valid test to turn on choke to see if 9K-rpm stumble from lean mixtures goes away, because it will not. Simply not enough additional fuel at 9K-rpms and +100% throttle to change AFR.

Conversely, if choke really did add sufficient fuel to fix 9K lean spot, on perfectly working bike, turning on choke will cause it to stumble at 9K from being too rich on other side of stoich. We know that this doesn't happen, as we also know it doesn't fix 9K stumble from lean mixtures either.

Yeah, tape up half filter test, will just make bike slower. Won't stumble though. You have to replace filter with one that actually stumbles, then do testing with modified AFR to see which way, richer or leaner, removes stumble.
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Old August 18th, 2019, 05:27 AM   #6
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You have to replace filter with one that actually stumbles, then do testing with modified AFR to see which way, richer or leaner, removes stumble.
I thought that was obvious.
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Old August 18th, 2019, 09:09 AM   #7
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I thought that was obvious.
He stated he didn’t want to put stumbling filter back in. So I responded with there’s no way to test without putting that filter in.
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Old August 18th, 2019, 02:37 PM   #8
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Quote:
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He stated he didn’t want to put stumbling filter back in. So I responded with there’s no way to test without putting that filter in.
Whoops I meant I don't mind putting the filter back in
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Old August 18th, 2019, 04:24 PM   #9
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Quote:
Originally Posted by nocturncal View Post
I been troubleshooting a hesitation around 9k with the throttle wide open, and finally solved it! Some questions though...

I just took out a CICMOD Air filter that I bought from Amazon a year ago, and cleaned and reoiled and put in a K&N filter that came with my bike when I bought it from the previous owner (when I bought the bike 10 years ago, I didn't know it had a reusable air filter and bought another air filter off of amazon, and decided to just use the Amazon one).

After the K&N was put in, I started having a hesitation with the bike when WOT at 9k where it would stop accelerating unless I backed off the throttle. I took the K&N filter out, cleaned the CICMOD Air filter, and put that back in. It solved the hesitation issue!

Im trying to understand why is this. The K&N filter seemed loose inside the air box, vs the CICMOD which fit very snug in the air box. I had roughly 6mm of play on both sides of the filter. Could it be the K&N filter was loose, casing air to get past the filter and cause the bike to run lean?

Reading the 250 manual in the section about air cleaner element cleaning, it talks about plastic holders that go between the stock air filter. My bike never had these plastic holders. Is the holder needed on aftermarket filters like the K&N?
Did you clean and oil the filter?
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Old August 18th, 2019, 04:28 PM   #10
nocturncal
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Did you clean and oil the filter?
Yup, cleaned both filters with the K&N cleaner, let it dry overnight and oiled with K&N oil.

Using the cleaned and oiled CICMOD filter, the bikes runs smoothly with no hesitation.
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Old August 19th, 2019, 06:33 AM   #11
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Originally Posted by nocturncal View Post
Yup, cleaned both filters with the K&N cleaner, let it dry overnight and oiled with K&N oil.

Using the cleaned and oiled CICMOD filter, the bikes runs smoothly with no hesitation.
I'm not a huge fan of K&N filters, but one of the biggest issues is over-oiling. I've done it before. Doesn't take much to block flow.

My son's VFR had a K&N when he bought it. Surprisingly for a "high flow" filter the actual filter area was less than a stock filter. He replaced it with a stock filter but I can't recall if it changed the way it ran or not.

I'd just run what you are running and sell the K&N. Lots of people love them.
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