Jetting Experts Apply Within

After I got my 00 426 running tonight, I took 'er out for a little spin. I've done the BK Mod, but still have a slight bog on the bottom. Time to turn towards the jetting. Right now, I'm running a 162S main jet (the S must mean stock), 42 pilot, 2-3/4 turns out on the fuel screw, and needle clip in the middle. I'm thinking of going down to a 158 pilot and 2 turns on the fuel screw. Anyone have any other suggestions, or will this setup work? I've never had to mess with jetting much, so any help/pointers/tips would be appreciated. FYI, I'm running a stock headpipe with an FMF PowerCore IV SA (the old round core design).

[ April 23, 2002: Message edited by: cowboyona426 ]

A slight bog on the bottom probably means you need to lean out the pilot circuit but either turning IN the fuel screw, or putting a smaller pilot jet in.

I would try a smaller pilot if fuel screw adjustments don't help. I made myself insane chasing a bog when all it turned out I needed a smaller pilot.

Originally posted by skthom2320:

A slight bog on the bottom probably means you need to lean out the pilot circuit but either turning IN the fuel screw, or putting a smaller pilot jet in.

I would try a smaller pilot if fuel screw adjustments don't help. I made myself insane chasing a bog when all it turned out was that I needed a smaller pilot.

What is your altitude and temp up there bud?


Here is what I ended up with on my 00 after:

1: Bkmod

2: Blue Wire

3: Carb Clean

4: Beer Drinking

A: Pilot 45 - Turns out 1 3/4

B: Main 168 - Depends on alt, Temp and Weather may drop to 165, mainly 168

B: Needle = Cir clip 1 down from stock Note This raises the needle 1 notch

C: Bkmod / Duration is set for about .5 + - 1

Only issue I have is duirng the bike getting warm the damn things stops running at idle from time to time. This goes away once the bike is a operating temp.

Starts first kick every time, No Bog just pure adrenlin rush out of corners

Thump, Thump, Thump, Thump

Your really a long way out on the fuel screw. Try setting that at 1.5 turns out. Personally I think if your more than 2 turns out on the pilot screw, you need a bigger pilot. Some guys have lost the screw with adjustments like yours.

Cowboy whats the altitude there where you ride? This can make a huge difference in settings.

Altitude right at home is about 3,000 feet, but I go up in elevation where I ride from between 3,000 and a little over 8,000 sometimes. Temp ranges from 60-100 this time of year. The fuel screw is adjusted according to FMF's website for the pipe, but I don't think the stock setting was 2-1/4 turns out... I'm going to crank 'er in a little and try that. Also, how far in should I thread the accelerator pump cam stop? I still might be getting too much fuel spray from that still. Is the blue wire mod necessary? I've never had a fouled plug in the beast- it looked pretty black when I pulled it a few days ago but I think it was from running lean prior to cleaning the carb out. Also, I noticed a SMALL amount of oil today that came out of the crankcase breather hose- is this normal? Thanks for the help.

P.S. Ego, maybe if you send me some of that beer stuff you were talking about, my bike will run as good as yours :) !

[ April 24, 2002: Message edited by: cowboyona426 ]


Stock jetting should be pretty close for you until it gets hotter and/or you go over 4 or 5 thousand feet, but IMO the jetting on the ’00 can be improved upon almost no matter where you ride it.

I’ll start with what I run in my ’00 and ’01 at 4k to almost 6k ft. of elev. where I normally ride, usually between 70 and 95 degrees F:

1 mm of pump stroke (IMO easier than trying to put a stop watch on it)

160 main

4th clip EJP needle (please try this $12 part, just ask for a stock ’01 needle)

40 pilot

200 MAJ (stock)

~85 Pilot Air Jet (stock is 100 and will result in a lean condition at higher rpms and low throttle i.e. popping on decel w/ a 40 pilot. You can get an adjustable PAJ from Sudco 800-998-3529, two parts, spring and screw, total $14).

1.5 turns out on fuel screw

Given the above I would suggest that you are probably okay w/ stock main. You definitely need to lose the stock needle, swapping for the stock ’01 needle is the best $12 mod you can make to a ’00 YZF, and you should try it in the 3rd and 4th clip from the top. Once you settle on that I think you should try a 40 pilot and see if it runs better at low rpms and low throttle settings. Once you have decided between the 42 and 40 pilot, with your bike fully warmed up, set your fuel screw to whatever setting gives you the best idle.

If you do end up with a 40 pilot jet you will probably want to order the adjustable

PAJ from Sudco (or Carb Parts Warehouse) and start at about 85 or 90 or maybe even try a WR PAJ if one is handy (a 75 vs. YZ’s 100), because with proper idle mix and a 40 pilot your bike will pop a bit on decel.

Hope this helps you out some.

BTW stock idle mix is 1.75 turns out (in is leaner, out richer).

BTW, I predict that bog you are getting will go away as soon as you replace your stock needle with the '01 part.

My only input is that if you are going to start stepping down on main jets sizes, just go one size at a time. The next step would be a 160. From my experience in jetting this machine, small changes reap the largest returns. Besides, the main jet is very, very easy to change. I can change mine in about 5 minutes. Ride/test for at least a half hour before deciding that you need to make another change and start with a fresh plug.

[ April 25, 2002: Message edited by: Boit ]

Cowboy, print Hicks last message...he know's what he's talking about and has experimented extensively. The needle can make a HUGE difference. On the WR side, our bikes came with very weak jetting so most of us have been through it and some of our WR's would amaze even some of you YZ guys with the crisp power delivery (shhh, it's in the needle.) :D It seems confusing at first, but remember to make one adjustment at a time and ride it briefly. When working with the needle, just use one bolt in the tank, no shrouds, one seat bolt...that way you can pull it off quickly to try different clip settings. Set aside 1/2 a day to tweek and test. You'll be stoked with the results.

One thing though, it's time to ditch the factory suggested settings and start doing it by feel. You have some baseline settings. Pick up a Kouba T-handle for that pilot screw adjustment. Not only is it a must for fine tuning the bike QUICKLY while it's running, but you can easily reach under and tweek it for altitude changes.

Also, you need to visually set that accelerator pump and time the squirt. When you have it off again make note of how much of a turn on the screw affects the pump duration, then when you need to fine tune and it's back together you'll know that a 1/8 turn will result in "X". 1/2 second is a good starting point.

Enjoy. :)

PS- oil from the breather is normal.

[ April 26, 2002: Message edited by: Scott in KC ]

all sounds there or theere abouts. i would recommend a EMN for your altitude and there are a bunch of EMN's for sale at the moment via mattnohiohills. the dealer ghas nine of them in stock. matts on the WR side.

you should all be using the 160MAJ for more overrev as well as dropping the MJ 10 at the same time for more roll-on response.

Hick's 40PJ/85PAJ is close to my 40/75. check the PS setting by just doing little pop wheelies everywhere and adjusting the PS underneath.

the PS shouldn't be used to set the tickover, it should be used to help acceleration. having sorted that the needle straight will look after the idle and start-up of your machine.

like i said there or there abouts.


It took me 5 minutes to figure out what a tickover was! GoodGawd! English man English! Oh wait a minute, not the queens english, use something we'll all understand! LOL

me thinks the web is bigger than we thought!

I'm with you Shawn! Taffy, please put all that in stupid hick terminology for me would ya? I'm from Idaho, give me a break! :)

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