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I ended up with a 155 main, 45 pilot, and removed the airbox lid completely. It rips now!

Motodeficient wrote:My bike is a 98 kdx220r with fmf pipe and silencer, boyesen power reed, and modified airbox lid. I just got my carb back from Fredette (was ported from 33-36mm). I asked them if they could jet it for my setup, and they said they could get it spot-on. I had a 145 main jet and 42 pilot jet in before, and they put a 160 main jet and 45 pilot jet in.... now the bike does not accelerate if you give it gas... it just bogs, not like the bog you get with a dirty carb, but more like detonation or something. What should I do?

160 seems rich for the main jet on this? but Fredette is the expert on these bikes!

Should i put my 145 main jet back in and see if it runs better?

I don't know if the main jet is the issue though because this is happening after about 1/4 throttle which is where the needle controls things right?

I can tell you first hand there is some difference in the jetting of the RB mod KDX and the Fredette mod KDX. I found out the hard way,Fredette jets his carbs 45 pilot 1173 needle 160 main. He says there is enough jetting info out there to get it spot on your self.

I will give you some info on my bike and conditions . 2000 KDX FRP ported cylinder, squish band head milling, carb bored to 36mm, Vforce 3 reeds, FMF desert pipe.

weather and conditions are a small but important factor.

NOW at 700 ft above sea level, temps 75 early morn to 90+ humidity 50-75% . pilot 42, needle CGM -3 or del or dem-2, main 155 .


One month or two, ago temps 55 early morn to mid 70's 45 pilot DEM-3 needle, 158 main.

I like mine to run spot on at all times my friends think I tinker to much. the kdx carb only takes 5- 10 minutes to change the jetting.

As you can see there are a few parameters you did not mention in your call for help. altitude, average temp, average humidity, what type of FMF pipe play a factor.

Motodeficient wrote:I ended up with a 155 main, 45 pilot, and removed the airbox lid completely. It rips now!

And that's about right!

Yup, best combo for a stock bike.

??? Its not a stock bike

For a KDX 200 with a 35mm carb... that seems to be the best jet combo with a pipe , reeds and air lid removed..... so it makes sense that your jetting would be in that range.... you will still need to fine tune it to get the optimum performance. You found a good starting point IMHO


Unfortunately... most on this forum don't know much about Fredettes carb modifications.

RE: 'Because I am a cheapskate :) '

Another happy consumer.

He got exactly what he paid for!!!

Sorry...a bad joke at your expense..and therefore completely un-called for and rectal-orifice-like on my part.

So.....you 'spekted something less?


I'd take the thing apart and make sure it's clean. Chances of metal shavings being in the wrong place are pretty good. That it runs good now doesn't mean something isn't still 'floating' around.

BTW: General jetting rule: Start rich, go 'down' from there.

Don't start lean and go UP. That's a bad idea.

Indawoods wrote:For a KDX 200 with a 35mm carb... that seems to be the best jet combo with a pipe , reeds and air lid removed.

What are you riding, 10 degree temps? I have exactly what you wrote, I'm at 150/42... I'm at sea level 70-90 degrees...

Don't ya hate how it changes through temperature all the time?

Well...your on the verge of 'splodin' then Buck if your running a stock carb....