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Old 08-09-2009, 10:41 PM   #1
randomwalk101
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carburator tuning

Friends,

I'm trying to tune my carb (again). I have ripped out the airbox and replaced with BMC pods filter and installed a factoryPro jetkit in my 08 ninja 250r. currently it runs great...much better than stock. However, there might be room for improvement and your suggestion is greatly appreciated.

current jet settings:

main jet: 112
needle: 3rd clip down
idle screw: 2.75 turns out

The bike pulls great (or better than stock)...but there are three noticeable "bumps". At 0-3000 rpm, bike pulls....then 3001-5,500 rpm bike pulls harder, then at 5,501 - red line, bike pulls even harder. Is this "normal" or am I rich in the "mid range"? I can pull out the carb and play around with the needle height and all but man, it's a pain. Some others 08/09 250 users also used 110 for mainjet and needle at 4th clip down...but they are in different state (diff altitude & diff bike). I would love to hear some suggestions and hit it the right way instead of trial & errors....save me some time and scrap nuggles Thanks..
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Last edited by randomwalk101; 08-09-2009 at 10:43 PM.
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Old 08-10-2009, 06:57 AM   #2
tomLSTD
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I don't think I understand your "bumps", so some questions:

Is it noticeable like a lag? Where you feel the power drop before it pulls again?

If it's a steady pull that just increases with RPM, I'd say it's normal. If it's a noticeable loss/ then gain, I'd say that you have issues with the needle movement (not too high or low), just that it's not moving like it's supposed to or there's a vacuum issue somewhere. Perhaps the diaphragm is pinched or mis-aligned?

By the time I get to this point in my tuning with carbs, if I haven't figured things out by this point, I take it to my mechanic.
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Old 08-10-2009, 07:24 AM   #3
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Quote:
Originally Posted by tomLSTD View Post
I don't think I understand your "bumps", so some questions:

Is it noticeable like a lag? Where you feel the power drop before it pulls again?

If it's a steady pull that just increases with RPM, I'd say it's normal. If it's a noticeable loss/ then gain, I'd say that you have issues with the needle movement (not too high or low), just that it's not moving like it's supposed to or there's a vacuum issue somewhere. Perhaps the diaphragm is pinched or mis-aligned?

By the time I get to this point in my tuning with carbs, if I haven't figured things out by this point, I take it to my mechanic.
thanks for responding Tom. I apologize for the lack of better terms used. I guess I should clarify your questions.
There isn't any lag and no power drop whatsoever.
What I meant by "bump" is that you can feel the "extra pull" in those rpm ranges. You and you can feel it pulls harder and harder as the rpm ranges go up. I was expecting a consistent pulls throughout the rpm range...thus the question. I don't think i pinched the diaphragm or anything..I was being extra careful it with & even put a dap of light grease to keep it in place while putting the cover back on so I think it's was installed correctly.
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Old 08-10-2009, 07:37 AM   #4
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Quote:
Originally Posted by randomwalk101 View Post
thanks for responding Tom. I apologize for the lack of better terms used. I guess I should clarify your questions.
There isn't any lag and no power drop whatsoever.
What I meant by "bump" is that you can feel the "extra pull" in those rpm ranges. You and you can feel it pulls harder and harder as the rpm ranges go up. I was expecting a consistent pulls throughout the rpm range...thus the question. I don't think i pinched the diaphragm or anything..I was being extra careful it with & even put a dap of light grease to keep it in place while putting the cover back on so I think it's was installed correctly.
Ok, sounds like it may be normal then, to an exent... Unless the bike is running poorly, I really don't think it's an issue.

The only way to be sure is to have it dyno'd with a 4 gas analyzer. That's what I would do. My dyno guy took care of my race bike in short order on the dyno- my jetting was waaaaaay off when I had a jet kit installed at another shop. Main jets were installed at the recommended sizes, but the guy was supposed to drill the pilot air jet and actually drilled the main air jet which fuxed everything up.

Anyway, a good technician on a dyno will be able to figure this out in short order for you.
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Old 08-10-2009, 08:51 AM   #5
Texas94fs
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If you are noticing lags of power it's an issue, or if there is a crazy surge then there might be an issue but if it is mostly progressive you should be fine. The slight bumps are probably the vacuum initiating first the needle and then the main jet.
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Old 08-10-2009, 09:26 AM   #6
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wideband gauge for the win!

i used to dread jetting because it took so much time. with the wideband, it gets me pretty close (if not dead on) everytime.
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