LarryCO's jetting no good on a 00 400.

I put a 38pj in my 2000 WR400, along with a 155 main and the EKP on #3 and the bike would barely run. Is there a huge difference in the carbs from the 00 400 to the 01 426, which is what most ride that have done this jetting? I thought the carbs were identical and the motor is just slightly bored larger. I wouldn't think this would make such a difference.

It's running decent now with the 155 main and the #3 EKP and the stock 42pj back in and 3 1/2 turns out. I haven't been able to order the 65 paj or the 160 maj yet. Should things change with these two jets to the 38pj? Also, you guys suggest replacing the paj with a pas that is adjustable. The Sudco rep told me to look into the Zip-Ty one because it's nicer than their's (gotta love those guys, sending you in the right direction at their expense). I think he misunderstood me, as this is the air screw on the bottom of the carb, not the jet inside the manifold. Where can I get this adjustable pilot air screw to replace the paj. Does anyone have PN's for the paj and maj, so I can order them?

Any input would be appreciated, as I apparently need help beyond the 01 426 setup for my 00 400 setup.

the pilot jet and your fuel screw are DIRECTLY related. If you are more than 2.5 turns out on your fuel screw >> go to a larger pilot jet.

As for the difference in 26cc (426 vs. 400), and a different carb venturi size (you sure about that? >> I do not know), the differences are substantial enough to cause you problems.

Also, swapping the main and pilot air jets will make a BIG difference.

The jetting that LarryCO has is excellent IF you remove the stock baffle in the exhaust and the airbox lid. By removing these to items, you will create a lean condition because of the increase in air flow. The 38 PJ and the 65PAJ combination will give more fuel in the lower end compensating for the lean condition.

I'm running almost the same jetting as LarryCo except for the PAJ. I found that with the Vortip that I am running, the jetting was too rich, (because of the added backpressure) so I increased the PAJ from a 65 to 75 and the bike runs like a raped ape...

Sudco Part Numbers for the Adjustable Pilot Air Screw:

021-230 1014-817-2000 screw

021-235 16052-KM4-0040 spring

Good Luck,



You need to make "the switch" to the 38PJ when you also change your pilot air jet. There's certain combinations of PJ/PAJ's that work well together...for e.g. 42PJ/75PAJ (stock on an '01). What I've found (through tons of help from Taffy and JD) is that changing to a 38PJ, while also lowering the PAJ to a 65 makes the low end of the bike "snappier". Some folks at sea level are running a 35PJ/50PAJ...but trying this combo didnt work nearly as well as the 38/65 at altitude for some reason. So I'm not surprised your results were very lean on your pilot circuit without reducing the PAJ...

Get the PAS from Sudco (or this other dealer) and try it again. Compare the 38PJ/65PAJ with the 42PJ/75PAJ and tell me if you think the bike has a snappier throttle response on the low end. Curious to see if it really is better or if I was just smoking something that day I switched... :)

Good luck!


I am uncorked and the airbox is opened up, so hopefully I'll get this to work.

I'm going to get the paj and maj and try it again. I know how to work on bikes, but jetting has not yet been grasped by my malnurished mind quite yet. Thanks for all of your help.

Alright, I just ordered the pas, spring and 160maj from Sudco. By the end of the week, I will have all the jets for Larry's setup.

I'm trying to educate myself about jetting, so if anyone can confirm or correct what I believe, please do. As far as what jet affects which part of the range in the throttle:

closed to 1/4: air screw and pilot jet

1/4 to 1/2: needle, main

1/2 to full: needle, needle jet, main jet and paj(pas)

What happened with the 38pj, 155main, EKP#3, 200maj, 75paj, 3 1/2 turns out was that at about 1/4 throttle the bike would cut out and refuse to rev.

When I went back to the 42pj, this went away. What is still wrong with the bike now is that there is a blip when the throttle is snapped from idle and it doesn't seem like it's pulling in the top end as it should. From what Larry has said, the 38pj in pairing with the 65pas and backing off the air screw to about 2 turns, I should be rid of that low end blip.


I also have a 2000 WR400 also and recently did some jetting work that I really like. See my signature for changes from stock. It may stand some fine tuning but it feels really crisp and clean with no ill-tendencies. No decel pop, crisp on snap-open, great roll-on, etc.

Good luck,



Two suggestions to get you educated on the affects of the various jets on the throttle range...

1. Spend $20 in the TT store and buy JD's Jetting Spreadsheet. You can put in different jets, temps, and altitudes and it graphically shows you the differences. Nice, informative tool to help you understand things.

2. I'm not sure it's still posted out there, or it's moved, but there's a Keihin Carb Tuning Guide online. I posted a weblink to it some time ago, but remember trying to go back to it a few weeks back and couldnt bring up the site. Do some searches for "Keihin Carb Tuning", find the link, and try it out. It talks about each jet (fuel and air) and explains what affect it has on your bike. There's a few mistakes, but very small's what helped me start learning in the very beginning.

If it's not there, I think I printed out a copy at home...I could fax it to you next week when I get back to CO...let me know...

Good luck!


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