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Discussion Starter · #1 · (Edited)
Ok, I have a 1991 honda 250x, and i have a cobra megaphone exhaust pipe on it, with a k&N air filter, and it has stock jets in the carb. Now i was wondering what kind of jets to run with it because of the pipe and air filter. And also, it is running rich with th stock jets too.

Thanks.
 

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Welcome to the forums. Someone will be around to help you shortly.
 

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Welcome to the forums... I would just change the main jet for what you have done to it, stock jet is 122 I would step to a 125 and do a plug test if it is still white step up to a 128 main. also make sure yuou back the pilot screw out about 1/8 to a 1/4 turn and reset the idle.
 

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Oh and not to hurt your feelings but the cobra exhaust does nothing for your performance, it only makes the people behind you deaf...lol try HMF, FMF, or Curtis Sparks if you want to see H.P. gains.
 

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Agree^^^^^^^^!!!
 

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if its running rich try pulling that air box lid off and running it that should lean it out. I run open air box on mine. but you shouldn't be running rich with stock carb settings. what did the spark plug look like when you pulled it out?
 

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If you have stock jets in your carb i highly doubt your running rich. I agree with moose we need to know what color your plug is when you pull it out.
 

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Discussion Starter · #10 ·
Every time I pull it out it pitch black, but I just clean it up and sand blast it and it's like new again
 

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Are you positive your jets are stock?
 

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Maybe the float valve is stuck open, letting it flood, causing the plug to be black.
 

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That could be but no matter what with those mods his carb has to be rejeted.
 

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Discussion Starter · #15 ·
Yes I'm pretty sure tht they are stock cuz the main jet said 122 when I cleaned the carb the other day, andcould the plug be black from not replacing it? Because I haven't had a ne plug in about a year now.
 

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I would try a new plug and see. It's time for a new one, anyway.
 

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Discussion Starter · #18 · (Edited)
Well I was planing on buy a new plug anyway because of rejeting it, and like you said it is time for a new plug, and you can tell it's running rich because you can smell it when you ride it.
 

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jetting

I also have a 1991 250x and need jetting guidance. I installed an FMF Powercore exhaust and header, UNI filter, and it has four breather holes cut into airbox lid. The FMF website says to use stock jetting with that exhaust. I believe stock is a 122 main and 38 slow jet, which is what I have. Is that where I should start? Every other thread I read says to up the main jet for any mods. Any thoughts?
 
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