Jetting report

Questions and Answers about the best carb and Head mods available for the KDX.
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kick
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Jetting report

Post by kick » 12:23 pm Apr 23 2021

I managed to purchase one of these great RB carbs in March. Came jetted with a 40 pilot and a 152 main. Needle CEK-3. Currently at 40-155 CEK-4. I’m very happy with the “behavior” of this carb. Great performance throughout. I ordered an extended air screw from JD so my fine tuning will be easy. I ride at sea level and temperatures have been 60-70 degrees.

clappy379
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Re: Jetting report

Post by clappy379 » 09:48 pm Apr 27 2021

I was lucky to snag one in March too!

I’m in central NY. Mine also came with a 40 and 152. I had the air screw all the way in to get it to actually run so I swapped out for a 42. That mostly solved that problem, but I’m still learning how to dial it in right. It is much snappier down low with the change but trying to fine tune it.

It’s strong up top (I have the rev pipe) but I’m also wondering if I should try position 4.

kick
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Re: Jetting report

Post by kick » 05:34 pm May 04 2021

I had a lean bog off idle with the 152 and 3rd position. Moved to the 4 position and that took care of the bog. I’d rather be on the richer side so I put the 155 in. Running good with the air screw out about 21/2 turns.

Strange you need a 42 considering your probably at a higher elevation than me. All bikes are a little different. Nothing wrong with trying different clip positions. I’m also running the rev pipe.

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SS109
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Re: Jetting report

Post by SS109 » 03:08 am May 05 2021

2.5 turns out on the air screw? You need to step down on the pilot jet if that's the case. I've found I can run a 38 at any elevation with just air screw tweaks. A 155 will probably work fine but, if the 152 was working good on the 4th clip, I don't understand going up. You loose a little power and fuel mileage going rich and if you ever do ride higher elevations you'll notice that rich condition pretty fast.
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kick
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Re: Jetting report

Post by kick » 02:49 pm May 05 2021

2.5 turns outs puts me in that SSS with the RB carb. I can basically crawl around in third gear. My bike is tagged so I do some road riding to trails hence the 155 main.

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