James Dean Carb Kit Installed ~ I Need A Little Fine Tuning

Ok, I received my James Dean kit yesterday (thanks for the fast shipping). I got the kit installed today and did a few test rides.

What I was running:

Originally I had 160MJ ~ 48PJ ~ 70PAJ ~ 2-turns on Zip Ty fuel screw ~ Stock needle in 4 position from top. My air box is heavily modified w/left side cover opening. I have the GYT-R insert with tubes removed so it's just about a straight shot. Throttle stop has been short to YZ specs, 800 altitude.

My bike was really very close to dialed in with just a couple of issues. 1) The bike would bog and most likely die if the throttle was snap full on while sitting at idle, but while riding it was not a big problem but it seemed to me that the bike may have been a little rich on the low end. 2) The bike seemed a little lean on the top end sounding like the engine had reached the rev limiter. The front end would easily rise up in 2nd and 3rd when I jumped on the throttle.

The JD kit setting I am experimenting with:

170MJ ~ 45PJ ~ 70PAJ ~ 1 3/4-turns on Zip Ty fuel screw ~ JD (blue) needle in 4 position from top. The bike started and idled fine. I am sputtering on the low end mostly 0-1/4 and a little at 1/4-1/2 throttle. My top end is scary great, bike no longer seems like it's lean or hitting the rev limiter. The bike still has a small hesitation while sitting at dead idle, but it no longer dies when the throttle is snapped full on. I can no longer pull the front end up as before so I need a little fine tuning. I am wondering if I need to try a different needle position or go back to the 48PJ for starters.

I would recommend the kit to anyone who's considering. I believe with a little fine tuning the kit will have everything you need no matter what altitude you ride.

Drop the needle one clip (to 3) if that helps, drop it again. :)

Thanks for your response, I will likely experiment with the needle clip position next. I was really waiting for a few more replies/opinions before I tear into the carb again just to move the clip one position. As simply as this is, it still requires a great deal of time and no gaurantee until you try it whether it was the right move. Hopefully once other TT'ers order the kit they will post and with everyone's feedback the experimentation will be limited.

What are your temperature and altitude?

The sputtering condition sounds like it's rich. Did you try turning the fuel screw to 1 1/4- 1 1/2 to lean the idle & low speed?

Clip position #3 looks like the setting to try other than fuel screw adjustment.



James thanks for the reply. I did adjust the fuel screw to 1 1/4 to 1 1/2 turns with not much results. My altitude is around 800 and temperture here is high 80's low 90's but today it's 98 so far. I'll move the clip to position 3 and report back. Thanks

Regarding the hassle of changing the jets,

I dont know about the WR450, but on the WR426, it is very easy to change jets and needles. Do not remove anything. Just loosen the clamps that hold the carb. inlet and outlet boots. Then push the rubber inlet boot out from the carb, point in downwards and wedge it between the frame. Now pull the carb out from the outlet boot and you have plenty of room to rotate the carb and change jets or needles. No need to remove the seat and tank and all that stuff. You do not have to disconnect the throttle cables. With the throttle cables connected, you have plenty of free play and it keeps the carb. from falling. You can do the whole job in 5 min. tops. Try it. It is easily done on the trail. :)

Let me go on record now...I can't wait until Yamaha decides to put fuel injection on these WR's. I've never cared for any type of carb jetting but it's a necessary evil to obtain the performance we desire. :)

On changing the carb needle and jets on the WR450, it's not much different than on the WR426. If I am going to be doing a lot of testing I found it's easier for me to take off the triangular bracket that's in front of the carb off and then loosen the boot clamps and rotate or even remove the carb from the boots and make the necessary adjustments. This is really simple to do and no need to remove cables and hoses.

Stay tuned, I'll be posting more testing results with the James Dean carb kits later this evening.

I did some testing today with the JD kit. Before I started I marked my throttle positions 1/8 1/4 3/16 1/2 3/4 Full so I could accurately pin point where any problems might occur.

As suggested I moved the needle clip to position 3 and started with the fuel screw at 1 1/2 turns. I experienced nearly the same problems as before. Spuddering from throttle positions 1/8 to 1/2. I moved the fuel screw in to 1 1/4 and then to 1 with slightly better results but still spuddering. I tried the fuel screw at 2 turns and it was much worst. I then turned it back to just 3/4 and it improved but still had the same overall preformance. I could easily kill the engine after letting the bike idle and snap the throttle open.

I decided to move the needle clip to position 2. I started with the fuel screw at 1 1/2 out. Much of the spuddering was gone and now the bike sounds like it has a slight miss when holding the throttle at 1/4 to 1/2. Overall low end was much improved and the bike would accelerate hard on the low end but when reaching the peak throttle of 2nd, 3rd, 4th (and probably 5th) gears the bike would cut out and miss. I moved the fuel screw to 1 1/4 and then to 1 and it seemed to pull hard on the low end and still misses when peaked in any gear on the top end. I still have a slight bog from idle but much improved and not as easily killed by snapping the throttle open.

While the jetting is closer than before it still needs some ajustment. I'll wait for comments before I proceed with testing.

I am glad you are following my advice to mark your throttle opening positions. It is easier to determine what to change by looking down at the marks. Try pulling in the hot start slightly ( not full engagement) while running on the main and see if the cutting out stops. Mine cuts out when I am slightly rich on the main jet like hitting a rev limiter. Try coming down to a 160 or 165 main. I know some can cure it by going even richer. I have seen my bike behave worse when only slightly rich. Do not compensate needle position for your pilot. Your pilot is rich so try going down on it first. Ignore my pilot settings since I need a rich bottom end for my pipe but not for the stock pipe. :)


You've provided sound advice all along and I appreciate and value your opinion greatly. No doubt you have already saved me a mountain of time and frustration from your experience. :)

I've already changed back to a 45PJ. I think the only other PJ I have is a 40PJ. I'll be able to do additional testing tomorrow and I'll try the hot start trick first then I'll try lowering the MJ.


In the instructions there is a note on temperature and humidity:

"Use the RED marked needle for hot or humid conditions, for example if the bike starts to sputter at low speeds. The red needle will evenly lean the lower half of the throttle range."

The high 80's, low 90's and reaching 98F is what the note was intended for. By moving to a leaner clip position you are making similar changes, except the diameter is leaner on the red marked needle.

Please try the red marked needle. It will lean 0-1/4 throttle and have an effect on the idle mixture too, so stay with the stock pilot jet and the middle clip position.

The main jet may need to be leaner also from the description, so try the 165. The YZ/WR450's have a fixed main air jet that is different than prior years and may have an affect on some models.



Thanks JD,

I think you are right on and basicblues will get it tweaked in. I think the WR450's fixed 200MAJ allows for a smaller main jet than a 160 MAJ on some of the earlier WR's.

The off idle bog may be coming from too much squirt at the start of opening your throttle. adjust the screw where the throttle lines are. You want to have less time of squirt. I forgot whether that is CW or CCW. Should only take 1/2 turn either way. This is also a easy thing to change. :)

JD, Thanks for your input, I appreciate you keep tabs on this post. I was holding the red needle as my trump card, I knew that I would probably end up using it since we are regularly in the 90's now with 60~80% humidity. I mainly wanted to run a series of test with the blue needle to get a good idea how each change affects performance.

Per Indy's suggestion, I dropped the MJ to 165 with the JD blue needle still in position 2 with fuel screw 1 to 1 1/2 out. I large portion of the low end spuddering was gone and the engine really didn't sound like it was missing. Nice consistant tone but at 1/4~1/2 throttle, I could feel a little jumping/bumping feel like it might be missing. I also checked the top end and 2nd gear when pushed near peaked had a definite loss and when I pulled the hot start in slightly it had little or no change in just about any gear. The other gears seemed to pull fine all the way through. Overall the smaller MJ helped...

I'll will likely test the red needle tomorrow and post the result tomorrow night.

first time i've seen your thread and it screams that the MJ was too big all along.

you should try a 160 or 162MJ now. prefer 160. the needle is then going to be too low. that hesitant feeling that's new is coz when you lowered the needle you cut down the fuel here and did the same when you dropped the needle (that's twice in the same area).

so you should lift the needle back up one.


test 1 = 160MJ (good top funny fourth gear)

test 2 = raise needle. (spot on 4th mid throttle)

test 3 = 40 PJ (sharp bottom-possible poor from no to go)

test 4 = varying PS positions in snap-wheelie tests.(there!)

that should do it.


Taffy, Glad to have you on board, I've been following your other post with carb tuning. :)

On my last test ride the tempature was 98 with high humidity. I tested the bike with the needle in position 2 first and then on the next test ride I changed the MJ to a 165 because it was quick change and I wanted to see how it affected overall performance.

Today, we had a cold front move through and the tempature was 77 with 75% humidity. I wanted to see how the 21 degrees lower tempature affected the performance. I was able to get out on some back country roads and let her rip. Carb settings were still the same, 165MJ,45PJ,JD blue needle in 2nd position. I rode 18 miles total at various speeds. The take off low end performance is pretty good, easily pulls front end in 2nd and 3rd if you jump on it right. I was to ride at wide open full throttle several times for 2 or 3 miles. I got my trailtech to post 90.2 mph one time and the overall top speed was 87/88 mph. From a dead stop and running through the gears twisting the throttle as much as possible without flipping on the low end. 1st gear would start missing at 1/2 throttle. 2nd gear would start just a little past 1/2 and 3rd just a bit more and 4th would start about 3/4 throttle. 5th gear no problem in wide open. I could have been hitting the rev limiter but I am not leaning that way. Sounded too much like the engine was just missing. I tried every gear at various throttle positions. The biggest problem is still 1/4 throttle no matter which gear I choose. The hesitation or miss is more noticable in 2nd or 3rd gear but it still can be felt in 5th gear as well.

It's rare to have a lower tempature day like today so I thought it would be a good time to test the bike under different conditions. However slight it may be, tempature and humidity does affect the jetting performance.

OK,here is my experience so far with the JD jetting kit.

My previous settings were:

NCVQ 4th pos.




FS 1-3\4 turns out

All the free mods and running open pipe. Was very happy with this setup but always looking for more.

JD jetting:

Blue needle 4th pos




FS 1-3\4 turns out

Noticed improvements everywhere especially in the mid range and up. A little rich right off idle. Ran just a little rough while holding at a steady throttle position just off idle. Fuel screw did not adjust it out.

JD suggested I drop the needle to the 3rd position with no other changes. After a little episode of installing the plate on the slide upside down(you may have seen my post on that :)) I got to test it today at that setting.

So I am at:

Blue needle 3rd pos.




FS 1-3\4 turns out

I am very impressed! I thought my bike ran strong before. I rode to work today becaause I knew it would be hot this afternoon. At 5:30 this morning it was 50 deg. Bike ran awesome. Instant throttle response. I hit 80 on the high way and it was still pulling hard. No hesitations anywhere, absolutly awesome!

This afernoon it is 100 deg. Hardly noticed a differance in perfomance. Maybe a little rich but no sputtering or anything. If I was at any real elevation in this heat I would be too rich but I don't plan on doing much riding in 100 deg weather. All testing has been done right around 1000 feet elevation.

This setup is the best I have had yet for my 450. It freaking rips! Cruising at 40 mph in 4th I can just snap the throttle open and give a little tug on the bars and it just stands right up. It would come up in 4th before but it took a little effort.

I am very pleased :D


Way to go Lowedog!

I got my JD kit last weekend and will be doing the same this weekend. I knew JD would come thru for us. I will post my results next week. Lets keep the information going. :)


" I have seen my bike run worse when only slightly rich".

That statement on dead on. My 426 jetting trials EMP3 very good, EMP3 1/2 very good, hard to tell the difference. EMP4 I couldn,t get the bike over 30 mph. 1/2 clip to rich and your dead. With me missing was allways a rich condition. The pilot and main circuits there were minor changes when changing jets but the needle was real touchy. Lean was weak, and rich was missing. When I was testing the EKN needle, clip 2 was the best, 3 and 4 were terrible, but 5 was pretty good. Makes no sence to me but thats how it was.

Hey Guys,

Just installed my JD kit so I'm at:

170 MJ

Blue needle, 4th clip position

45 pilot

3 turns out on zip ty screw

Since it's raining here, I've only been able to garage test, but I'm mostly focused on the off-idle bog problem right now.

After confirming my slide is installed properly and checking the squirt timing and duration, I'm still seeing a problem - although it may be a little better. I'll continue to monitor this post as well and provide any feedback as I continue my tests. Anyone have any ideas on the bog. Seems basicblues and I are having the same problem. BTW, I'm at 1500' and it's been around 75 degrees this evening with very high humidity around 80%.

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