Carb Tuning for a 2004 KX 250

[Charlie500]

Any body have experience with these carbs? They are a bit different than the old K5 I had. I will be riding around 1000-2000 ft elevation. It looks like the carb has a Slow Jet, Power Jet, Main Jet, Float Valve Needle, Throttle Sensor and a Fuel Cut Valve..... Looks a little tricky....lol.... The bike currently has a Pro Circuit pipe and silencer on it. I plan on tearing the bike completely down and doing a good greasing / clean up on it. I will tear the carb apart and clean it... I'm not sure what jets are in it currently...

[KevinTwoStk]

My '00 KX125 has a Keihin PWK Power Jet carb on it. Is that what you've got, too?

As I understand it, the Power Jet allows you to run a leaner-than-normal main jet because the Power Jet adds raw fuel to the mixture at about 7/8 to wide open throttle.

From what I've experienced, tuning the Power Jet carb has been almost identical to tuning any other carburetor.

I saw an online recommendation for my bike from Motocross Action Magazine. Based on that, I swapped the #55 Power Jet for a #42. I leave the #42 Power Jet in place, and just tune the rest of the jets (including the main jet) as if the Power Jet wasn't there. Basically, leave the Power Jet as a constant, and let the rest of the jets be the variables.

Does JD Jetting make a kit for your bike?

[Charlie500]

My '00 KX125 has a Keihin PWK Power Jet carb on it. Is that what you've got, too?

As I understand it, the Power Jet allows you to run a leaner-than-normal main jet because the Power Jet adds raw fuel to the mixture at about 7/8 to wide open throttle.

From what I've experienced, tuning the Power Jet carb has been almost identical to tuning any other carburetor.

I saw an online recommendation for my bike from Motocross Action Magazine. Based on that, I swapped the #55 Power Jet for a #42. I leave the #42 Power Jet in place, and just tune the rest of the jets (including the main jet) as if the Power Jet wasn't there. Basically, leave the Power Jet as a constant, and let the rest of the jets be the variables.

Does JD Jetting make a kit for your bike?

JD Jetting does make a kit for the bike... Is it worth $76 though? How many people have experience with these kits? If it is guarenteed to make my bike run perfect (Carburator wise) I guess they are worth it.... I don't know... It doesn't say anything about the power jet on the JD Jetting web site...

[don46]

My '00 KX125 has a Keihin PWK Power Jet carb on it. Is that what you've got, too?

As I understand it, the Power Jet allows you to run a leaner-than-normal main jet because the Power Jet adds raw fuel to the mixture at about 7/8 to wide open throttle.

From what I've experienced, tuning the Power Jet carb has been almost identical to tuning any other carburetor.

I saw an online recommendation for my bike from Motocross Action Magazine. Based on that, I swapped the #55 Power Jet for a #42. I leave the #42 Power Jet in place, and just tune the rest of the jets (including the main jet) as if the Power Jet wasn't there. Basically, leave the Power Jet as a constant, and let the rest of the jets be the variables.

Does JD Jetting make a kit for your bike?

JD Jetting does make a kit for the bike... Is it worth $76 though? How many people have experience with these kits? If it is guarenteed to make my bike run perfect (Carburator wise) I guess they are worth it.... I don't know... It doesn't say anything about the power jet on the JD Jetting web site...

I have never used the JD kit, but I do know from my experience the needle is to rich, and I think you get several mains and pilot jets so it may be worth it if you figure how much a needle and mains cost. I've spent alot of money on needles and always keep 3-4 mains from about 145 all the way to 190 and pilots from 35 up to 65 so may not be a bad price, oh and you might get different power jets to.

[KevinTwoStk]

JD Jetting doesn't make a kit for my bike, so I can't comment on personal experience with them.

After reading the MXA recommendation to swap to a #42 Power Jet, I did the rest of my jetting via the trail-and-error method. I was amazed at the difference one needle clip position made.

Do you have an owner's manual and a factory service manual for your bike? I ask because with my 2000 KX, there are different jetting specs listed for U.S., European, and Australian-model KX125's. Oddly enough, my bike runs best with the Australian specs, however that's a function of the conditions I ride in, not the continent I'm on.

You might also find that the factory needles work better. They're typically triple-tapered, whereas many aftermarket needles have only a single taper. I was ready to buy some needles from Sudco, but was told about the difference between factory and aftermarket needles, and advised to stay with the factory needles.

[Charlie500]

JD Jetting doesn't make a kit for my bike, so I can't comment on personal experience with them.

After reading the MXA recommendation to swap to a #42 Power Jet, I did the rest of my jetting via the trail-and-error method. I was amazed at the difference one needle clip position made.

Do you have an owner's manual and a factory service manual for your bike? I ask because with my 2000 KX, there are different jetting specs listed for U.S., European, and Australian-model KX125's. Oddly enough, my bike runs best with the Australian specs, however that's a function of the conditions I ride in, not the continent I'm on.

You might also find that the factory needles work better. They're typically triple-tapered, whereas many aftermarket needles have only a single taper. I was ready to buy some needles from Sudco, but was told about the difference between factory and aftermarket needles, and advised to stay with the factory needles.

good to know Kevin, I have the service manual but it doesn't show much about tuning the carb.... it shows what the stock jetting is. I will just buy a few factory jets and dial it in my self.... thanks for the heads up on the power jet. have you ever had any issues with the TPS or the electronic fuel shut off valve?

[KevinTwoStk]

If there are any issues with the TPS or the fuel shutoff valve, I can't tell. Just like you did, I bought it used. However, everything's connected and the wires are in good shape, and it runs "normally." I guess that means no issues, right?

Relevant side note: the same basic carb settings have performed well from 1,800 to 5,500 feet. One of my favorite rides starts below 3,000 and ascends to around 5,500 feet. During the ride, I can't feel an appreciable difference in the way the bike runs.

I have found a local gas station that has 100 octane unleaded race fuel at the pump. It's expensive, but I don't have to buy that much of it. My 125 is pretty easy on gas, and I rarely ride more than once a week. The race gas is a good safety measure against pinging, and it (to my knowledge) doesn't change formulation from season to season. I'm in SoCal, and the pump gas varies quite a bit depending on the month. This approach has worked well for me.

I run Maxima Super M at 32:1.

[Charlie500]

If there are any issues with the TPS or the fuel shutoff valve, I can't tell. Just like you did, I bought it used. However, everything's connected and the wires are in good shape, and it runs "normally." I guess that means no issues, right?

Relevant side note: the same basic carb settings have performed well from 1,800 to 5,500 feet. One of my favorite rides starts below 3,000 and ascends to around 5,500 feet. During the ride, I can't feel an appreciable difference in the way the bike runs.

I have found a local gas station that has 100 octane unleaded race fuel at the pump. It's expensive, but I don't have to buy that much of it. My 125 is pretty easy on gas, and I rarely ride more than once a week. The race gas is a good safety measure against pinging, and it (to my knowledge) doesn't change formulation from season to season. I'm in SoCal, and the pump gas varies quite a bit depending on the month. This approach has worked well for me.

I run Maxima Super M at 32:1.

There is a gas station in my home town that sells 100 octane unleaded race fuel at the pump as well. I plan on running that in the bike. I have about a case of bel ray h1r i plan on running in the bike. I used to run it in my 500 at around 40:1... I also have a case of bel ray gear oil 75w I think.... Do you think that will be ok to use in the tranny?

[STM Suspension]

I ran the stock needle in my 04.  I live at 5000 ft, and typically ride up to 10,000.  I just kept going leaner on the slow jet until it stopped fouling plugs, then tuned the main.  It pulled hard.

I've run the Bel Ray 75 in the box with good results.  I now have an 07 250, and have used the Bel Ray as well as the Redline.  I think some of the Redline fluids are hit and miss, but their tranny fluids are amazing.  I use and recommend (and sell) the Redline tranny fluids.

I use the Redline 2 stroke race oil now, and have used H1R, both mixed at 50:1.

[Charlie500]

I ran the stock needle in my 04.  I live at 5000 ft, and typically ride up to 10,000.  I just kept going leaner on the slow jet until it stopped fouling plugs, then tuned the main.  It pulled hard.

I've run the Bel Ray 75 in the box with good results.  I now have an 07 250, and have used the Bel Ray as well as the Redline.  I think some of the Redline fluids are hit and miss, but their tranny fluids are amazing.  I use and recommend (and sell) the Redline tranny fluids.

I use the Redline 2 stroke race oil now, and have used H1R, both mixed at 50:1.

I'm down to a 158 main and 50 pilot it still seems rich. I still have the stock power jet.... How lean can I go? Bike is still rich on top....

Pro circuit recommended 165 main, 50 pilot nafg needle second clip from the top 50 power jet.
Is the nafg needle leaner than the nalf? I have the nafg in the bike now.

Service manual recommends 52 pilot, 165 main, nalf needle second from top, 50 power jet.

[Charlie500]

The bike has the pro circuit works pipe and pro circuit silencer/spark arrestor. I just changed the packing in it. Bike seems to be running really rich. Any help would be greatly appreciated...

[sandblaster]

Here is what Pro Circuit recommends:
2004
MODEL    MAIN    PILOT    NEEDLE    POS    SCREW    POWER    SLIDE    
KX 250    165     52             NALF    2        1 1/2          50          8.0

[sandblaster]

Just thinking out loud....
Do you know what the compression is?

[Charlie500]

Just thinking out loud....
Do you know what the compression is?

I don't have a compression tester, but the bike feels like its got good compresstion.... the bike is almost brand new.... very very low hours

[Charlie500]

Here is what Pro Circuit recommends:
2004
MODEL    MAIN    PILOT    NEEDLE    POS    SCREW    POWER    SLIDE    
KX 250    165     52             NALF    2        1 1/2          50          8.0

The jetting suggested above seems to be way too rich.... especially on top.