2004 CR250R +Mods Jetting Suggestions

Fly-n-High · Jul 15, 2004

I was wondering if anyone would have any suggestions about jetting this setup. I have a 2004 Honda CR 250R with the following mods (1000FT above sea level running 93 octanne fuel):

1. FMF Fatty pipe and Titanium 2 silencer
2. Boyesen RAD Valve array with Pro Series reeds
3. Boyesen exhaust flange (replaces stock unit)
4. iCAT spark manipulator.

Between the recommendations by each manufacturer I'm confused. Any ideas on where to start? The only thing I have changed so far is lowering the main jet from a 420 to 410. Spark plugs keep fouling and it is so confusing to a novice mechanic. Thanks! :bang:

bedell99 · Jul 15, 2004

I need a bit more infomation. How is the bike running?? Your ability?? What rpm range do u ride?? Give me baseline stock jetting for this year??? What oil and ratio???

Erik

Fly-n-High · Jul 15, 2004

Stock Jetting 04 CR:

Main Jet: 420
Pilot Jet: 30
Needle Clip Posit: 2nd
Air Screw: 1.5 out

The bike seems to start and run fine. The problem comes off idle and it seems to bog and the throttle response is slow. mid and top seem to be responsefull, but being a novice it is hard to specify what the bike is actually doing.
As far as ability, I ride around the intermediate level and try to keep the bilke reved high, but my trails are tight and slow at times.

I run Honda HP2 at 32:1 ratio as recommended.

Thanks for the feedback........

bedell99 · Jul 15, 2004

The first thing I would do is ditch the stock sprocket for a 50 tooth if you ride slower more technical trails. The 04 has even less bottom than an 02-03. The next thing I would recomend is an S-8 nozzle. This is what the main jet screws into. It will help. I think the pilot and needle positions are fine. If your run low rpm's which is how trails are. You will benefit from a lower main. I will give you an example on how riding style will affect jetting. I ride motocross no trails and keep my bike at at half to full throttle on wide open grand prix tracks that are prominent in colorado. My bike runs perfect at these tracks and they are mostly at 5000-6000 ft. About 2 times a year I will go to grand junction which is a trail type setting, mostly play riding. The bike usually runs very rich down there and it is at a lower altitude I think around 4400ft. I barely ever use full throttle even half throttle for that matter. The bike would benefit from leaner jetting because of how I use it. This is the point I'm trying to get across. Jetting is soley dependent on the rider and type of riding. For your type of riding you would benefit from leaner jetting across the board. Also a larger sprocket in the rear to get some more bottom end, which this bike has hardly any. First get an S-8 nozzle then try try going to a leaner main jet. Like a 390-400, then play with will the needle clip. i bet you will notice the harder you run this bike the better it responds. Also the clutch is your friend, you will have to slip it alot to get it to run cleaner. Don't be afraid to ring its guts out.

Erik

Fly-n-High · Jul 15, 2004

Erik,

Thanks for all the help! I have a few questions with regards to your suggestions. What purpose does switching to a S8 nozzle do? I'm trying to get a picture of what to change and why (riding style, conditions, etc.).

What type of system or how do you know what to change for jetting (a step by step diagram)? Is it a exaact science based on variables or is it a approximation based on experience? Maybe a flowchart diagram or something

This also helps me for when I change riding conditions (like you mentioned) and terrain. I would like to have a "set" of jets that can be changed depending on what type of riding and conditions are present.

Once again, thanks 4 the help.......

bedell99 · Jul 15, 2004

What I noticed with this nozzle is it cleaned up the response right after 1/4 throttle. Its not a cure all, end all fix but it did help. With this bike I had no really way to go except I knew that most of the published jetting cures where complete BS. I would read forums on all the sites and most people where going the wrong way because they thought that the poor throttle response and bottom end was caused from a lean condition. I actually started to join the boat until i realized i was going in the completely wrong direction. I just took it upon myself to go to the track armed with a bunch of jets and see what combination worked the best. It took me all day. I also noticed that alot of people that post on these sites, that they do not race motocross and use these bikes for trail riding or practice track riding which is completely different than racing a bike a competitive level. I know RC, Larocco & Fonz use completely different spec's than what the average person will and i guarantee it is much richer because they are constantly wide open for long periods of time. Another big factor is the type of gas you use. Pump gas is very inconsistent, not that it is bad but you will never be able jet your bike crisp using it. Most people don't have to, you can get it pretty darn close, but never perfect. If you are going to use a system, I would start with the pilot jet first, then needle than main. More your throttle tube with increment 1/4,1/2/,3/4 and go from there. I know its a bit tedious especially with our bikes but change the jets one at a time. Good luck.

Erik

Fly-n-High · Jul 16, 2004

I appreciate your findings and perception of this task. It seems more systematic in ways over conventional means. I believe it is like any other hobby, the longer you are involved, the more you learn. I have had bikes all my life, but this my first time analyzing the factors of engine performance (no one to tune it for me).

One question about the S-8 nozzle, what is it referred to when ordering it. I looked at the 02-04 service manual and noticed the piece is different between years. It appears it is a one piece item for 02 and 03, but 04 has two separate pieces. My local dealer had no clue of what I was looking for.

Thanks again.....

bedell99 · Jul 16, 2004

here is the part number: go to any yamaha dealer and gove them this number:
3TC-14141-S8-00 NOZZLE,MAIN (S-8)

It is what the main jet screws into.

Erik

Fly-n-High · Jul 19, 2004

Thanx Bro. I plan on heading to the dealer today. Are you sure the part will be interchangable to a 04? By reading the service manual, it seems the nozzle piece is two seperate items in the carb. Any suggestions about this for the 04?

bedell99 · Jul 19, 2004

I can't 100% guarantee that it it will fit beacuse they went to a carb with a TPS but you can remove in quite easily and you don't even have to remove your floatbowl to check it out. 1)Loosen the clamps and rotate your carb to get access to the bottom bolt that hold's on the float bowl. Remove with 17mm box wrench. 2) Remove your main jet. 3) Get a deep socket 10mm and remove your nozzle. The nozzle is what you screw your main jet into. 4) Give it a close inspection, you should be able to see a S-9 stamped on to it.5) drive to the local Yami dealer and and give them the part number.6) put it back together. Enjoy.

Erik

Fly-n-High · Jul 20, 2004

Thanx again, I ordered the part number you gave me. I appreciate your description of how to remove the nozzle. It will be easier then following the service manual. Once it is in place and jetted, I will let you know the results!

Fly-n-High · Nov 3, 2004

FYI on 04 CR

FYI the 04 CR has a different carb that contains a different two (instead of one) piece nozzle. I believe the stock is a S-7. Just a FYI for anyone tha read this thread with a 04 Vs a 02 or 03 CR 250R........

Sandy Whoops · Nov 3, 2004

Bummer that you struck out with the S-8 nozzle. Going back to your original complaint (bogging off idle) - try adjusting the air screw. Turn it out (left) to lean out the idle circuit. Adjust it in 1/8 turn increments. Take a test ride after each adjustment Adjust it for best off idle throttle response. If the idle speed increases, readjust the idle. If you reach 2 1/2 turns out, then it's time to buy a new pilot jet 1 size leaner (ie 27.5).

If, after setting your idle circuit, you still experience the bog then consider buying a new needle that's 1 step leaner than your current needle. The last two digits of the needle # indicate the diameter of the straight section. If your current needle is, for example, a 6BDZ30-73 then you'll want to buy a 6BDZ30-74.

It's a good idea to keep an eye on your spark plug while adjusting the carb. If the tip becomes white, you're too lean.

Throughout this jetting exercise, listen for engine knocking at 1/8 to 1/4 throttle. Don't know if the 04 is susceptible to this, but the '02 certainly is. If you experience knocking, then you'll need to richen the pilot circuit and / or the needle. Or blend some high octane fuel in with the pump gas.

Fly-n-High · Nov 5, 2004

Thanx for the info, but I had someone jet the bike for me. I prefer to ride the bitch rather than tweaking it. It was a great learning experience, but you know the difficulties with this CR.......

gotta love those CRs over the CRFs!!!

Fly-n-High · Aug 7, 2005

JD Jetting Kit Works Wonders

If you read this thread and have a 02-05 CR you can agree that the low end well SUCKS!

I agree that Eric G has the "Premier" solution, but a quick fix would be a JD Jetting Kit. It is fairly self explanitory with some minor tweaking to reach the full potential. His needle designs seem to turn that Mikuni (with TPS) into what it was designed for. If I knew more about assembling engines (I don't wanna **** it up), I would get-r-ported by Eric.

Rock on!!

:aj:

Wilky · Aug 8, 2005

JD Rocks

I second the JD kit. I messed with my carb a lot and the JD kit is the only thing that made a real difference. Throttle response and low end were much improved. It starts up easier too.

Scott

+30 · Aug 8, 2005

JD kit

Is the JD kit in addition to the s8 nozzle everyone is talking about 02-04CRs, or does the kit contain a nozzle?Did testing take long with this kit?

oldfrt613 · Aug 9, 2005

JD Kit works great with stock nozzle - best money I've spent on a newer style CR ( case reed )

+30 · Aug 9, 2005

jd kit

thanks ordering my kit 2day.

Fly-n-High · Aug 19, 2005

I have a S-8 nozzle for sale if anyone is interested. I bought it and it is for 02 and 03 not 04!

+30 · Aug 19, 2005

JD kit

Well, tried the JD kit and cant seem to get a full range out of any combination. Mid to upper is nice and crisp-almost too lean on kits red and blue needle 3rd clip settings.Most of the problem is Idle to 1/4. Plug shows good color after a 3rd gear kill so it would seem main jet is about on. Pilots dont help the no-idle situation or the bog off idle.Dont think any air leaks present because stock set up idles about average, and is predictable at least, but no "grin factor" as they say. I have an s8 maybe Ill go back to stock needle and plug the s8 in with the 420 or a 410. Btw, why did Honda go from a 380 in 02 to a 420 in 03?
vp u2
no motor work
usual bolt ons

2004 CR250R +Mods Jetting Suggestions

Fly-n-High

bedell99

Fly-n-High

bedell99

Fly-n-High

bedell99

Fly-n-High

bedell99

Fly-n-High

bedell99

Fly-n-High

Fly-n-High

Sandy Whoops

Fly-n-High

Fly-n-High

Wilky

+30

oldfrt613

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+30

Fly-n-High

+30

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