Jetting

crs

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May 7, 2001
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#1
I have recently purchased a 93 kdx200. I would like to know if anybody could give me a suggestion as to what the jetting should be so that I have a good Idea of what to start with. The bike has a fmf pipe, modified silencer, and a Rad Valve. I am running Golden Spectra mixed 42:1. I ride in the desert at about 2000 feet with a temperature lately of around 90 degrees F.
Thanks,
 

crs

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#3
Need jetting help fast.

I read through the carb tuning on the Justkdx web site and found it very helpful but I'm still having some problems. I'm new at this and I don't have much expierence. When I bought the bike it had a 148 main jet, 48 pilot jet, #6 slide, r1172n needle one clip from the top and the air screw 1-1/2 turns out. The outside of the plug would look really black and oily but the color was brown down inside the plug. I havn't done a plug test at wide open throtte because I havn't found a place yet where I could hold it open for that long. I usually only open the bike up all of the way open for short periods of time and never usually ride much above third or fourth gear. The bike ran good except for at low speeds. I had to turn the idle screw way up to get it to idle. By backing the air screw way out I could get it to idle real well. Last night I changed the pilot to a #45. I followed the instructions for adjusting the air screw and found that I achieved maximum Idle at about 4-5 turns out on the air screw. I found that the bike ran good at low speed like this. Real clean with out a lot of smoke but when you open the throttle all of the way really fast it cuts out. If I turn the air screw in to about .75 out and turn the idle screw up so that it will idle the bike won't run well at low speed but it doesn't cut out when you open the throttle fast. I know I should drop the pilot down one more size but I think that this will make my throotle response worse yet. Please help I need the bike for this weekend.
 

Canadian Dave

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#4
Was that a 148 or 158 main jet?

Use your air screw to tune for the best possible throttle response. At 4 turn out the circuit is so lean it bogs when you wick the throttle open. 0.75 turns out sounds too small/rich. Try opening up the air screw to about 2 or 2.5 turns out and test and see if you have a bog when wicking the throttle open. I'm guessing there will be a slight bog. Turn the air screw in 1/8 of a turn at a time until the lean bog disappears. This should put you in the ballpark. You may need to continue to play with the air screw until its just right or drop down to a 42 pilot jet.

From the description of your plug it sounds like either your jetting was/is too rich at some point or that your plug is too cool. I'm guessing you are running the factory BR9ES. I'd try switching to a BR8ES so the plug will run a little hotter and stay a little cleaner.

David
 

crs

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#5
Dave thanks for the reply. It is a 148 main jet that I'm running. It seems like when I turn in the air screw so that it doesn't bog then it smokes a lot, runs rough and sputtery at low speeds, and it is hard for it to idle. When the air screw is out it idles great and the low end is really smooth. Would moving the clip down a notch on the needle get rid of the bog when the pilot is leaned out to run good?