2003 CR 250

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7/10/2018 4:43 AM

So, I got this bike for a steal. Bike has very low hours, less then 30, all stock except for an FMF pipe and silencer. My problem is with the jetting and idol. I cant seem to get the jetting right. I went with what FMF has recommended for the pipe and year, and thats a 400 MJ and 40 PJ. I feel like it loads up and is running very rich. My air screw was 1.5 turns out as well.
Does anyone have any idea whats going on??

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Kevin Windham, The man, the myth, the legend! Gonna miss seeing this man on the line.

-----Do or Do not, There is no try-----

7/10/2018 5:09 AM

Welcome to the Mikuni... its a bit picky. Once you find your best setting it can run very well, but it seems to be a bit more sensitive to altitude and temperature than the other carbs. Most long time owners have made the swap to the keihin. The JD kit is a good way to find a good set up with the mikuni, but I still never was 100 percent happy with it. Then theres Lectron and smartcarb etc ..Lucky dog finding a low hour 03!

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7/10/2018 6:48 AM

I've never used a 40 pj in any of my mukuni equipped CR2's. Not sure what FMF was thinking when recommending such a lg. pj unless it's a misprint. The stock pj for the 03 is a 35 so the 40 is 2 sizes larger / richer. What are your current temps, humidity & elevation ? I assume it's the stock oem needle ?
FYI - I tested with many pipes when these bikes 1st came out & the FMF Fatty was by far the worst performer IMHO. It was a mid-range pipe as it concentrated the power in that part of the powerband.

One of the main issues is the oem S-9 nozzle that came on the 02-03 CR2 mikuni's. Honda changed it to an S-7 (2 sizes leaner) on the 04-07 models shorter version tmx equipped with TPS.

I tried a JD kit as well & didn't like it so I went back to the oem needles. His kit back then came with an S-4 so it shows you how much leaner he went with the nozzle. He has since reconfigured his needles a few yrs. ago to work with the oem S-9 from my understanding.

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Speak softly and carry a big stick.

7/10/2018 8:08 AM

H4L wrote:

I've never used a 40 pj in any of my mukuni equipped CR2's. Not sure what FMF was thinking when recommending such a lg. pj ...more

As you know the 01'-03' long bodied Mikuni TMX's were different from the 04'-07' short body TMX-x, and thus used a different series needle jet. the 01-03 carbs used I believe a 644 series needle jet ,where as the 04-07 used a 914 series needle. I don't think that the flow rates for the different series needles jets were the same. that's why Honda changed the needle jets from an S-9 for the 01-03's vs, I believe an R-8 for the 04-07's. The s-4 would be for the 04-07 bikes, and is the correct needle jet to use for that bike.

I picked up another 07 cr250 last week and will be doing a bunch more testing with that carb and bike soon. I'll test it back to back against my 07' cr250 equipped with a 38mm PWK.

I owned an 03' cr250, but have since lost my notes for that bike with the TMX carb. I believe I used an s-7 needle jet, along with 1mm removed from the slide cut away. I think they came with #5 slides. A 32.5 pilot the stock needle and a 410 main.

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7/10/2018 10:05 AM

H4L wrote:

I've never used a 40 pj in any of my mukuni equipped CR2's. Not sure what FMF was thinking when recommending such a lg. pj ...more

Im in the midwest, roughly 600-900 elevation. Temps are in the low 80s to mid 90s. Ill try and go down on the Pilot Jet. It is the stock needle.

The low end seems to be ok, but wont open up mid and top end.

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Kevin Windham, The man, the myth, the legend! Gonna miss seeing this man on the line.

-----Do or Do not, There is no try-----

7/10/2018 6:33 PM
Edited Date/Time: 7/10/2018 6:35 PM

Your elevation and temps should be pretty close to mine. I'm running a 27.5 pilot, 390 main, 6BEY30-74(stock 2002 cr250 needle) clip position 2, S-7 needle jet. My 03 runs great with this set up when the temps are warmer. I will go up one size one the pilot and main as the temps start to drop this fall. All this talk about the Mikuni being a bad carb crack me up. Pro Circuit platinum pipe here.

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No brains, No headaches.

7/10/2018 9:49 PM
Edited Date/Time: 7/11/2018 4:19 PM

H4L wrote:

I've never used a 40 pj in any of my mukuni equipped CR2's. Not sure what FMF was thinking when recommending such a lg. pj ...more

digger wrote:

As you know the 01'-03' long bodied Mikuni TMX's were different from the 04'-07' short body TMX-x, and thus used a different ...more

Digger that is correct as I mentioned above the Mikuni's short & long body being different versions. As far as the flow rates are concerned I would think would be minimal. The bigger difference will be in the size of the nozzle going from the S-9 down to an S-4 for example.

Below are PC's recommended jetting specs. Just choose the yr. & it will show the 02-03 using a stock oem S-9 & the 05-07 using an S-7. https://www.procircuit.com/jettingspecs3.htm

The S-4 nozzle in the JD kit back then was recommended for the 01-03 TMX. Same needles were also used for the 04-07 short body equipped with TPS.

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Speak softly and carry a big stick.

7/10/2018 9:59 PM

Mx4life320 wrote:

Im in the midwest, roughly 600-900 elevation. Temps are in the low 80s to mid 90s. Ill try and go down on the Pilot Jet. It is ...more

I'd suggest starting with PC's recommended jetting specs on the 03 & fine tune from there. Keith posted his jetting specs with similiar conditions as yours.

JetsRus still has nozzles available for the mikuni's to be able to fine tune the carbs.
Scroll towards the bottom of the pg. & it will be the 633 series nozzles for the 01-03 TMX Mikuni.
http://www.jetsrus.com/a_jets_by_carburetor_type/needlejet_jets_mikuni.htm

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Speak softly and carry a big stick.

7/11/2018 10:54 AM

With my 03 CR250, I found the TMX to be easier to jet once the squish was made a bit smaller. Use a head gasket from a 05-07 and it'll drop the head down a little bit. A little bit means I don't remember the actual numbers, just that it worked since the squish from Honda was too big. I eventually moved to an Airstryker, but that gasket helped more than I expected.

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