Rejetting with 2 different size jets??????? - TwoWheelForum: Motorcycle and Sportbike forums
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post #1 of 32 (permalink) Old 08-03-2007, 05:03 PM Thread Starter
 
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Rejetting with 2 different size jets???????

After I put the new exhaust on my bike ,the directions for rejetting called for 2 different sizes. 2 smaller on the outter 2 cylinders and 2 larger on the inner 2 cylinders. Can anyone help explain why
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post #2 of 32 (permalink) Old 08-03-2007, 06:39 PM
 
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no idea. gas man probably knows.
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post #3 of 32 (permalink) Old 08-03-2007, 08:11 PM
 
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If it's air-cooled, maybe the inner cylinders run hotter and need one size larger.
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post #4 of 32 (permalink) Old 08-03-2007, 08:46 PM
 
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i think it has to do with the bike not having a airbox, but still being a full fairing bike, dead air area under there
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post #5 of 32 (permalink) Old 08-04-2007, 10:21 AM
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Actually it has to do with the EPA. The manufactures will always lean out 2 of the cylinders to help meet air emmisions requirements. For my 9R it was the 2 inner cyclinders.. just like your say yours are. No big deal. Once you install the correct jets all 4 will be firing equally and also creating more power cause after you own it.. who gives a hoot what the epa says.




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post #6 of 32 (permalink) Old 08-04-2007, 10:42 AM
 
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never thought of that 1. if thats the only reason tho, i have a question-i thought all jet kits were labeled for "off-road use only", so why would they still want to use dif jets to meet a rule/standard that doesnt apply?


i assumed it was a airflow issue because ive only seen the dif sizes for full fairing bikes-the naked bikes seem to have the same size jets all across.

so whats your thoughts on that?
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post #7 of 32 (permalink) Old 08-04-2007, 12:20 PM Thread Starter
 
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Ok the bike is a 1998 liquid cooled CBR 900rr with the stock air box still on it and a K&N air filter. So if this is an EPA requirement That means nothing to me and the bike is running good then no biggie right??????
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post #8 of 32 (permalink) Old 08-04-2007, 03:23 PM
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Originally Posted by dnyce View Post
never thought of that 1. if thats the only reason tho, i have a question-i thought all jet kits were labeled for "off-road use only", so why would they still want to use dif jets to meet a rule/standard that doesnt apply?


i assumed it was a airflow issue because ive only seen the dif sizes for full fairing bikes-the naked bikes seem to have the same size jets all across.

so whats your thoughts on that?
The aftermarket jets will say that...cause its illegal for you to modify the carb jetting. Because then it may not pass epa emmisions law.

And what's your other question?

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Ok the bike is a 1998 liquid cooled CBR 900rr with the stock air box still on it and a K&N air filter. So if this is an EPA requirement That means nothing to me and the bike is running good then no biggie right??????
If you haven't modified the air intake or exhaust.. and its running fine and the spark plugs tell the same story your butt is saying... then yes just leave it. Don't fix it if it ain't broken.




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post #9 of 32 (permalink) Old 08-04-2007, 04:53 PM Thread Starter
 
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Allrighty then !!! Thanx for the info to every one who had input
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post #10 of 32 (permalink) Old 08-04-2007, 10:55 PM
 
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The aftermarket jets will say that...cause its illegal for you to modify the carb jetting. Because then it may not pass epa emmisions law.

And what's your other question?
you're saying that the reason for the two dif jet sizes from the factory is strictly a epa thing. so, since aftermarket jets say "off road use only" because its illegal to modify the jets, why would the aftermarket kits still use two dif sizes?

does the epa regulate off road use only vehicles too? i didnt think they did, otherwise it seems there would be no reason for the term "off road use only" because EVERYTHING would be illegal.

basically im saying if its strictly a epa thing, why dont the aftermarket jets tell u to use the same size jet straight across? seems like it would make more power that way...unless its not strictly an epa thing, and it has to do with performance/bike design/airflow. does that make sense? it sounds alil confusing maybe, but i think you can see what im asking. if not i can rephrase it i guess
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post #11 of 32 (permalink) Old 08-04-2007, 10:57 PM
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Quote:
Originally Posted by dnyce View Post
you're saying that the reason for the two dif jet sizes from the factory is strictly a epa thing. so, since aftermarket jets say "off road use only" because its illegal to modify the jets, why would the aftermarket kits still use two dif sizes?

does the epa regulate off road use only vehicles too? i didnt think they did, otherwise it seems there would be no reason for the term "off road use only" because EVERYTHING would be illegal.

basically im saying if its strictly a epa thing, why dont the aftermarket jets tell u to use the same size jet straight across? seems like it would make more power that way...unless its not strictly an epa thing, and it has to do with performance/bike design/airflow. does that make sense? it sounds alil confusing maybe, but i think you can see what im asking. if not i can rephrase it i guess
99.9% of our aftermarket exhaust are for off road use only
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post #12 of 32 (permalink) Old 08-04-2007, 11:03 PM
 
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yea i know-thats what im saying. "off road use only" basically lets it slip past the epa requirement right? so why would a aftermarket jet kit not take advantage of the same loophole? why vary the jet sizes to adhere to a rule that doesnt apply to the product? doesnt make sense, unless its NOT just an epa thing.
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post #13 of 32 (permalink) Old 08-04-2007, 11:28 PM
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Originally Posted by dnyce View Post
yea i know-thats what im saying. "off road use only" basically lets it slip past the epa requirement right? so why would a aftermarket jet kit not take advantage of the same loophole? why vary the jet sizes to adhere to a rule that doesnt apply to the product? doesnt make sense, unless its NOT just an epa thing.


I'll let ya know when I put a stage 2 kit in my F4 this winter

And a ignition advancer
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post #14 of 32 (permalink) Old 08-04-2007, 11:54 PM
 
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I'll let ya know when I put a stage 2 kit in my F4 this winter

And a ignition advancer
it would be sweet if you put the stage 2 kit on there, dynoed it, then put the the same jets all across in it and dyno it again, once with the smaller of the two sizes, and once with the larger of the two sizes. dyno time can be expensive tho, so i dont expect you to go thru all that trouble...but if you do
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post #15 of 32 (permalink) Old 08-05-2007, 05:52 AM
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OIC... sorry mis-read...

Is it a stage 1 jet kit? I believe those may still be legal and designed more for adjustments to the jetting for humidity and altitude.

When jetting a bike... you really want a stage 2.

Beyond that... I'm not sure. I know when my 9R was re-jetted it was to all one size. Many times if you're running dyno-jet kit or in my case it was a muzzy jet kit.. you can call the manufacture of the jet kit, tell them what mods you're running and where you are located (for altitude) and they will give you a jetting size to start with.




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Last edited by Gas Man; 08-05-2007 at 05:54 AM.
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post #16 of 32 (permalink) Old 08-05-2007, 07:59 AM Thread Starter
 
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Thumbs up

I am under the influence that the difference between a stage 1 and stage 2 is stage 1 is only jets, stage 2 in jets ,needles ,springs, and air filter. If thats the case I put a stage 2 in it . As far as the story my spark plugs are telling me,Everything is fine. They are all nice and evenly coated tan. The bike runs fantastic and pulls harder than before.(WHIPLASH)
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post #17 of 32 (permalink) Old 08-05-2007, 08:41 AM
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But to get the most power gain.. you need everything in the stage 2, along with a good air filter and exhaust.




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post #18 of 32 (permalink) Old 08-05-2007, 08:52 AM Thread Starter
 
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That is why all this came about , I bought a new exhaust, The K&N air filter and jetting were both recomendations by the exhaust manufacturer . My original question was only why they would call for 2 diff size jetts thats all. I thought that normally they would all be the same size across the carb rack.
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post #19 of 32 (permalink) Old 08-05-2007, 09:22 AM
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They being the jetting manufacture? What brand jets did you get?

I suggest calling them and speaking to somebody from their tech dept.




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post #20 of 32 (permalink) Old 08-05-2007, 09:32 AM
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Quote:
Originally Posted by Gas Man View Post
But to get the most power gain.. you need everything in the stage 2, along with a good air filter and exhaust.
I have the air filter n exhaust But I dont think it has stage 2 kit in it, may have a stage one, but I dunno. I'm also gonna install a ignition advancer. Any recommendation on one of those?
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