Need help after Mod's

O Ring/Gasket that goes between the two metal/aluminum (whatever it is made of) parts of the carb, it is installed and in good shape

>> you are all set! :)


You are doing great. If you are wondering why all these guys know so much about YZ/WR carburation it is because we have all been in your spot. The thing is, your bike is SCREAMING air leak. Also I wanted to tell you to check that your accelerator pump is pumping when you twist throttle. Remove the carb again. Time yourself. I got to where I could remove mine in about 4 1/2 minutes. Then fill up your float bowl with fuel. Then twist the throttle. If you are looking into the head side of the carb you should get a small spray of fuel right in the eye. I did. Gas in the eye really feels good. Anyway if that accel pump is squirting that's good news. When you reinstall that carb make sure those air boots are TIGHT and well sealed. Another post suggested WD 40 to check for air leaks.

Good Luck,

I know how much fun this is. :)

Mr. Lee

Another thing. On the WR carbs there is this thing on the side called an Octopus. It is that mess of hosing on the side of your carb. This thing is a disaster and no one is really sure what it does. You need to eliminate it. This can be done easily by installing a YZ #100 air jet. It is located right behind the air horn. Also this is a common one that gets clogged with dirt. It is also easy to miss. after you have installed the YZ air jet put vaccum caps over all of the nozzles that stick out. Then connect the hot start hose directly to the nozzle in the head. Big source of air leaks eliminated.


Thanks for the encouraging words.

I have learned soooo much in the past few weeks. I did have the carb off again last night. I would guess it took me about 6 minutes. :) The pump is squirting gas. Towards the back of the workbench now instead of my eye. I readjusted the slide and plate with the adjuster screw and locknut. Put it back to where it was origonaly. I am really thinking I didn't get the carb sealed off the first couple times playing with the jetting. I spent a good 20 minutes last night checking I got it tight this time after reinstalling the carb.

I am going to pass on the "Octopus" (for now). But I may PM you after I am sure I get everything else under control, and think of doing that mod.

I will try the bike out after work today and post how it goes. Thanks again!

the octopus (aka AIR CUT VALVE) actually works AGAINST you as you adjust the fuel screw.

I cannot recall exactly Yamaha's point of the octopus. Clark Mason, our long time carb guru, claimed it was only used during starting and that it interfered w/ fuel screw adjustments.

Because of the numerous hoses, it is only an accident waiting to happen. Clark snagged his octopus on something and created a vacuum leak directly into the intake tract, then on into the intake valves finally getting to the piston/cylinder.

You can only hope you do not damage your cylinder, depending of course on what the engine sucks in, should this same thing happen to you.

As for swapping out the main air jet to a 100 (like the YZF400), I would wait. Depending on what needle and main jet you go to, a 100 MAJ may not be the answer. Bill, our Senoir Moderator and myself, are using some jetting specs after extreme exhaustive R & D from Taffy in England. You gain performance, and an increase in fuel economy. I know, it sounds backwards but it is really true.

To remove the octopus, all you need is two rubber vacuum caps (1/8"?) found at most automotive stores (heck, maybe even Wal Mart??).

You will just be re-arranging the lines and fittings on what you already have. The ENTIRE octopus will be removed.

I used silver soldier, flux and a torch to fill up the brass nipples on the carb >> Worked like a champ!

Bill's jetting specs:

de-octopussed Thanks Clark!,

Accelerator pump: KL Mod,

Factory jeting by Taffy:

Needle: EMM #2,

Pilot Jet: 38,

Pilot Air jet: 55,

Main jet: 158MJ,

Main air jet: 160MAJ,

Slow jet: 60SJ

Fuel Screw: 1.5 FS at 500-2,000'


Clark Mason also helped me to remove my octopus. Clark is a really nice guy and he responded to my e-mail without even knowing me. Luckily I removed the octopus before it created any problems for me. (thanks to clark). I would not mind putting up a web page that details this mod, that is if anyone is interested. Clark is the one who actually recomended the YZ MAJ. Anyway Mr. Lee if you are not interested in doing this mod right now no big deal, just thought it would be a good idea while you had it off.


OK guys, now you have me rethinking the ACV "Octopus" Mod.

John, If you create a web page with the details... I'm there Dude!

Here is where I'm at after readjusting the slide plate last night:

The bike starts 1 to 2 kicks with choke. Idles pretty good after warm-up (Without choke, YES!). Sounds like it might need the timing adjusted but I'm not so sure on that. It still wants to die after snapping throttle back REALLY fast. If i slowly roll back on throttle, it is fine. It surges when cruising in first gear with the throttle pulled back ever so slightly. It has the backfire deal again on deceleration.(Not too bad of a backfire issue but noticable). Other then that the bike is great. Front wheel comes up nicely once you get past that 1/8? to 1/16? throttle.

My thoughts now are to adjust the fuel screw to fine tune it all. (Maybe not though after hearing about the ACV Mod)

What do ya think???

Here is my jetting setup:

Main Jet = 155

Pilot Jet = 38

Pilot screw 1 and 1/2 turns out.

Starter Jet = 60

Main Air Jet = 160

Pilot Air Jet-1(Pilot Air Screw from Sudco) = 65 or 1/2 turn out.

Pilot Air Jet-2 (Slow Jet?) = 90

Jet Needle = EKP, clip on #3

(ie LarryCo jetting-Thanks Larry!)

Mods are:

Airbox lid removed.

Grey Wire cut.

Taffy Mod.

Throttle Stop shaved.

I have the stock exhaust with plug removed, and I ride between 6 and 10K elevation. Live at about 5K elevation.


Mr Lee,It sounds like that slide plate adjustment helped out quite a bit!!!!!! Great.It sounds like you need to play with the fuel screw and or your pilot curcuit.Try bringing the fuel screw out to see if that helps.If you end up more than 2 full turns out (richer)You might need another size up on the pilot.(0- 1/4 throttle is controlled primarily by the pilot curcuit)try this first before you de-octopus.That procedure is'nt all that difficult if it needs to be done.Kevin NH or others with older WR's can help with that.Also you might want to check the exhaust header/silencer connections-make sure they are snug.Poor or loose exhaust connections can cause backfiring on decelleration too.Glad you are heading in the right direction. :)

Mr. Lee

Here is a link to Clark Mason's Page. This link takes you directly to the octopus removal page. This site also has much useful information on WR carburation. web page

Mr. Lee

You said the bike ran "ok" last summer before it sat for a few months. Does that mean that it did not have the off idle hesitation. Did all of these problems develop after sitting? I am just making sure we are not rejetting a bike that ran fine last summer. Because if that is the case I would definately take a look at that timing chain.

My timing chain wore and jumped time.

Just making sure we are solving the right problem.


Oops...see below (stupid 2nd page!) :)


Way cool amigo! Sounds like we're close now...

Yes, play with the fuel screw to fine tune. Mine's set somewhere close to 1.5 turns out, but I cant be sure about that as I've probably changed it somewhere down the line.

Good test: Make sure you're bike's warmed up completely. Go wide open in 4TH gear, then let off the throttle completely. Check to see if the bike "pops" OR "backfires" OR decelerates without either occuring. If it's popping, you're slightly lean on the pilot circuit. If it's backfiring, you're slighly rich. If neither, you're money. This is a good test for the PAJ/PAS setting as I've been told.

To lean it out, go up on the PAJ by 5, then retest. To richen, go down on the PAJ by 5, then retest. I would play with the fuel screw first though before playing with the PAJ settings (as it's easier - no carb pulling! - and you can sometimes fix small problems this way). If no luck with the fuel screw, set back to 1.5 turns and change the PAJ setting accordingly...

Overall, I think you'll end up at the 65PAJ/PAS during the summer, but you may need some fine tuning between now and then. Just my $0.02 (I dont get to do much riding in the spring I havent ever had to change the PAJ setting from 65).

Next test would be to try a thicker needle (EKQ) back with the 65PAJ and various fuel screw settings...dont think you'll need to get this far though...

Report back the results...



RSA210 & Larry,

I will try the fuel screw first. I would really like to get the Kouba tool to adjust that, but the wife already thinks I have spent way too much on the "Toy" already. (Also had to get a new throttle cable assembly). It was about to break on the return cable.


I'm sure I will end up doing the "Octopus" mod eventually. Thanks for posting the web page with the ACV info. BTW, the bike ran OK last summer (OK for my standards). I bought it last Spring and the only bike I rode before that was a 99 DR350. So to me it was a huge difference and seemed fine. It did have the low end bog and the plug was very very black after a few rides last summer.

I may be lucky enough to get a ride in this Sunday so I can do the Pilot Circuit test. (Thanks Larry)

I will post the results after that.


I finally got to take the bike out for a ride today. Unfortunatly I broke the tip of the fuel screw, so I have a Kouba screw/"T" handle on it's way. :D

With the screw out to 1 and 1/2 turns (I think. Broken tip makes sit hard to adjust), the bike dies when pulling back fast on the throttle, + the surging at light throttle. After turning out to 2 turns, it doesn't die when snapping throttle + the surge is gone. I still get the poppig on decel. Now it is just a matter of dialing it in with the fueal screw and PAS. :D

Thanks soooooo much to all that replied to this post!


RSA210 :D

HareAndHound :)

NH Kevin :D

LarryCo :D

You guys are awesome!!!

Have A Drink On ME! :D


Havin one right now

My bike pops on decel after I put those white brothers tuning disks on my exhaust. I'm too lazy to get it perfect. Don't have one of those fancy quick adjusters.

When you wanna make your bike Colorado fast we will help you change your timing and carb to YZ. My dad lives in CO and I know you need a beefy bike to ride out there. Glad we could help.

Glad to see your making good progress :grin

BTW- you will LOVE the Kouba,makes tuning for off idle throttle response a breeze,Now go RIDE THE THING :):D :D

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