If there are any mistakes, please PM me, or e-mail me about it.

Here we go!

I created this while cleaning out my carburetor, and it is not necessary to completely take the carb off of the quad if you don't want to.

After each explanation is a picture. Sorry if some of the pictures are blurry, the next time I have my carb apart I will take better pictures. Enjoy :)

First off, clean your quad! You don't want any dirt or any type of anything besides gas getting into your carb. That will be bad news.



Next, remove your seat, gas tank side plastics, and gas tank cover plastic.



Next, make sure that the petcock valve is in the "On" position, so that only a minor amount of gas will leak out. Pull the gas tube from the carb, and let the gas leak onto a towel. Then, pull the other tube coming from the petcock to the carb. Then, remove the two bolts that are holding on the gas tank, and remove the gas tank.



Next, go up to the throttle body on the handlebars, and remove the cover. Then release the cable from the jig thats in there. Then just unhook the cable from the body. I suggest putting the throttle body cover back on so that nothing gets in there.



Then, unscrew the choke cable from the side of the carb (For those of you with a carb mounted pullout choke, you do NOT have to do this). Then, you may loosen the boot clamp screws on both the airbox and engine sides. Remove the carb.

Now it is easier to work with (Again, you do not have to completely remove the carb to rejet! I find it easier to work with this way though). You should have something like this:



Now, I recommend getting some type of pan to put the carb in, because in this next step, gas will pour all over the place.

Turn the carb upside-down. Remove the Idle mount screw. Remove the four screws holding the bowl on. Remove the bowl



Now, from here you can do many things. I will list 3 things, because I do not have pictures for the rest.

Changing Your Main Jet

*For the "Changing Your Main Jet", and the "Changing Your Starter Jet" sections, pictures will be posted before explanations...*



To change your main jet, it is very simple. Take a flathead screwdriver and remove the Main Jet. Replace it with a larger/smaller main jet (Stock size is 130 Mikuni Small round). That's it, you're done.

Changing Your Starter Jet

*Refer to above image*

To change your starter jet, do the same thing as you did with the main jet. unscrew it with a flathead screwdriver, and replace it with a larger/smaller starter jet (Stock size is 60).

As you can see, jetting is very simple, its just getting it spot on that takes time. Let's continue...

Adjusting The Needle Jet Clip Position

*Explanations posted before pictures*
**Note: If you have a stock needle, you will not be able to adjust your needle jet due to the fact that the stock needle only has 1 position!

First, you start off with this...



Second, remove the 2 screws holding the big black cap on (Carburetor diaphragm cover), so that you get something like this (Watch out! HUGE spring under the cap!):



Then, remove the slide (diaphragm) by slowly pulling the rubber boot upward.



Next, take a pair of needlenose pliers, and reach down into the slide with them, grab a hold of the gray needle holder, and pull (WATCH OUT! There's a tiny little spring that will shoot across the room, and will never be found because it makes no noise).

Next, if you want it to be leaner, move the little clip up a position on the needle. If you want it to be richer, move the needle clip down a position. This may take a little patience, because sometimes the clip does not want to move.





When you are done with rejetting your quad, reassemble everything back together, it is fairly easy.

You're done. Now all you have to do is check your spark plug after riding it for a while. Black plug = rich... White/Gray plug = lean... Tan/Brown plug = Perfect (this is very hard to obtain though... Just make sure that your not lean, or too rich)

I will update this thread with how to change your pilot jet, and adjust the Fuel mixture screw as soon as my carb is apart to take pictures again.

Hope this helps anyone with jetting questions. Have fun!

Not bad at all - "cockpit valve" should be "petcock valve."

Wow great directions. I will have to save those. 8) :D 8)

OK, a couple comments.

1. NEVER remove your carb completely when it is this dirty. Contact dirt will brush off and fall into either side and either lodge in the carb or go into your engine.

2. If you are going to remove the carb completely get something to cover the boots leading to the inside of your filter and your engine. Either that or stuff it with a clean rag. You really don't want anything to get in there.

3. If you don't have to remove the carb completely, then don't pull the hoses. You CAN rejet very easily without removing the carb from the bike. However pulling the hoses again leaves you open to contamination.

4. For anyone running below 3000 feet start on the third clip, anyone over 3000 feet start on the second clip. Also be very careful with the slide, its pretty delicate and you could easily break it.

5. Your bowl is held on with brass phillips head screws. These screws strip VERY easily and are installed very tightly from factory. Don't even try using a screwdriver simply get yourself an impact driver.

Blaster this is a pretty good start but it needs some polishing.

One more thing that everyone should understand. Separate circuits overlap depending on throttle position. If you look at the diagram below it explains where different portions come into play. So if you are having a full throttle stumble you can see its probably between your needle and main jet. I'll see if I can find a better diagram that pulls in all the circuits, but this is a good place to start.

Thanks mang! BTW, I covered #3 in my post

What does the starter jet control?

It does basicly what its called. It controls how much fuel is let in during the starting/warming up of the engine. From then on out, the other jets control it.

i think u skipped step one

"First off, clean your quad! You don't want any dirt or any type of anything besides gas getting into your carb. That will be bad news."

but overall great job!!!!

Lol, I actually did clean near the carb and such, there just arent any pics... I did clean the plastics and such, just not the undercarriage

kickass!! this will mos def help me out, somebody get this man a beer

Yeah dude nice work... :schweet:

i have to rejet tommorrow (if the kit comes in), so i will print this and use it for reference...thanx.

Thanks guys, glad its going to be put to use!

blastmaster, is the air mixture screw shown in your pics by the slide? that brass plug with the hole in it. is that it. can u tell me what the best way to get to it. i was told i have to drill out the plug. please help

After jetting for the second time, I have found that jetting is simple. The hardest part is finding the best jet, but luckily changing the main jet is so simple I could learn how to do it by reading a internet discussion (pictures help ALOT).

The hardest part is the clamp on the rear of the carb. The head of the screw is at an awkward angle and the screwdriver hits the side of the tank. This is causing me to whore out the phillips head. I think I will change clamps to the hex head style so I can get a nutdriver on it instead.

Oh, and you don't need an impact driver for the bowl screws. I put the screwdriver in the screw head and hit the screw driver with a hammer a couple of times. This was enough to break that crazy tight bond that was there. The second time around, the screws are not as tight.

Yes, jetting does get easy after doing it a couple times. And yes, it is a pain to find the perfect jet for what you have. Ya know... What you could do is rotate the clamp to your preferred angle so you dont hafta fight with it every time. Also, some people just prefer to use an impact right from the start. I had a problem with the srews too, but as soon as I got em off, I put on allen head bolts. Much much easier. Anyway, have fun with jetting, its easy. I should be updating this as soon as I have a digi cam handy.

Sorry, I didn't see your post. I personally have not messed with the sir mixture screw yet. But yes, I've been told that if the plug is there, you have to drill it out. Don't hold me accountable for that, though, as I have not done it myself.

ok i thought the first step was to clean the quad ,,is it just me or did you skip that part... lol

^^

Does anyone have a better picure of the needle setup. Is it necessary to use the spacers with the dynojet needle that came with the bike stock. If so does anyone have a pic of what it looks like.
Thanks,
Joe

The bike belongs to a buddy of mine. The bike is stock with a uni airfilter and snorkel removed. The jetting we are at currently is needle in 2nd position and a 140DJ jet. Does this sound right?

Joe

I just spent the last 6 hours learning about jetting my (stock Mikuni BSR36) '04 Z400.

I purchased a "Stage 3" engine kit. It contains:
DMC Alien complete exhaust system.
K&N filter
Outerwear filter cover
Dynajet jetting kit

I needed a larger main jet than was included in the kit, and after calling
8 different bike shops here in Phoenix, NO ONE STOCKS DYNAJET MAIN
JETS SEPARATELY. I was forced to either order a different Dynajet jet kit
(with larger main jets), or use "generic" Mikuni jets with the stock Mikuni
needle (which every shop has in stock). I chose to stick with the Mikuni
parts, as they are readily available.

Some more things I found:

1. Dynajet jets (as marked) are smaller than other brands of jets!
A 150 Mikuni jet is close to a 160 Dynajet jet.

2. Dynajet needles DO NOT WORK with non-Dynajet (main) jets!

Dynajet needles have a different taper than other brands of needles,
so they do not seat properly with non-dynajet (main) jets.

If you use a Dynajet needle (and Dynajet main jet), and go somewhere to
ride that would require a change of jetting, you may not be able to get a
Dynajet main jet. Almost every bike shop has "generic" mikuni jets that work
with Mikuni needles.

DON'T GET ME WRONG. Dynajet jet kits are great as long as you have the
correct jet in the kit, and you don't plan on re-jetting while on riding somewhere
where a change of jetting is needed.

Yes it is necessary to use the stock spacers UNLESS the dynojet kit comes with its own set of spacers. I don't know whether it does or not because I have not purchased one yet. Use the stock spacers unless the dynojet kit came with one.

As for whether the jetting is right a 140DJ is leaner than a stock Mikuni main jet, therefore at 3/4-full throttle, you are lean. Go up 1 or 2 sizes on the MJ, and you should be good. But, if it runs without any popping on decelleration, no stumbling during acceleration, and the plug isnt't white or too fouled, you should be good to go!

Yes, Dynojets are measured differently. Im not sure, but one of them (Mikuni or dynojet) is measured by hole size, while the other is measured by flow rate. Also, here is a chart that compares the 2 sizes (credit to Crazie for this):



Have fun ;)

Mikuni mains do work with Dynojet needles. That is the best way to go. With a Dynojet kit you are paying for a lot of jets you'll never use. Get Mikuni main jets that cover you 2 or 3 up and 2 or 3 down from the correct jetting and you're in there.

I just noticed, the 9th pic down should read "Carburetor Diaphragm Cover", not "Carbutetor Diaphram cover". Oops.

hey i went from a yoshi full system to hmf slip and i took out the starter jet and it said 60-i thought it ment 160 so i should take out the main jet or do u think ill be good with the yoshi jetting

You may need to lean it a little if I understand you right. Going from a full to a slip-on leans it a twee. I really couldn't understand wat you said.

i have a 2004 ltz400 i just replaced the stock exhaust with a yossi full replace stock filter with a k/n filter and filter lid i live at sea level in california and i gess that i will need to use a dyno jet dj155 main does this sound right also were should i start my needle setting and pilot :uh

Yeah, start at 155 DJ MJ... 3rd clip down on the needle, then 4th if that isn't enough. 25 Mikuni PJ.

hey Mash1up, that is exactly the same set-up i'm going with. let me know how you make out.

also hey blastermaster, how come there is no mention of changing needle jets or throttle valves. it seems everything is centered around the main jet, needle, and pilot jet. are those the only things that need adjusting?

this forum and this post sure is informative and it's gonna make me feel alot more comfortable tearing into my quad.

thanx guys!

I was wandering if anyone could let me know about where to start with a jet size. I cut out the baffles from my stock silencer as is posted in another forum. It is otherwise stock. I am at 1440 feet above sea level. Thanks in advance for the help. Also, thanks for having such a cool and useful site.

when I had a modded Stock Pipe on my 04 I ran a 150 MJ with the air box lid off. Ran really good but im around 150ft above sea level

Did you have to change your needle at all? And how does the plug look?

i was useing a 155 dyno jet main but top end started to bogg so i gess that i was to rich i went down to a 150 dyno jet main and i did'nt see the point in adjusting the rest as they seam very good any way what doyou think blaster

You really shouldn't need to rejet for this. At the max you would go up 1 size on the mai n jet.

Need more info... I'm guessing that it bogs on acceleration at about 3/4 throttle? If it bogs while accelerating, then it's rich. Back down 1 size at a time until the bogging goes away then you know that you're spot on. The other stuff (Needle and PJ) should be fine.

hay guys bike is running real good but for some reason today it bogged a litle in secornd gear balls out any surgestions plug looks good
150 main dyno
stock needle
stock pilot

Well for one, you SHOULD need a bigger pilot and an adjustable needle with those mods. But, some people have weird situations in which they don't need it. I would back down 1 size on the main. But I would strongly suggest that you at least get a 25 PJ and an adjustable needle. Also, you might want to mess with the A/F screw. Does it backfire at all when you let off the gas?

O.K. i have read enough and felt confident enough to tear into my quad last night and here's the result. it's an 04' Z, yoshi comp. full exhaust, pro-flo kit, k&n filter with outerwear, k&n lid w/outerwear. i used a dyno-jet jet kit. i used their needle on the 3rd setting,dj 160 main, stock pilot and mixture screw at 3-1/2 turns out. It started instantly (which is a surprise because in stock form it was a w00ter to start this time of year), and after a thorough warm-up and a ride through all the gears (down the road and back) it seemed really good.


Here are a few questions:

1) on the diagram that blastermaster posted, is the starter jet also refered to as the pilot jet? if so mine is marked "60". i have seen several recommendations for a "25". can someone please explain this?

2) is the pilot screw also called the mixture screw? if so i beleive my stock setting was only 1/2 to 3/4 turn out. is that possible?

3) i'm not sure exactly how to describe this but when rolling down the road, accelerating through the gears, when i was in 3rd gear and "double clutched" trying to gain rpm's and dump the clutch it didn't respond the way i expected. is it because of the rev limiter or is my jetting not quite correct to get the optimal performance or what?

4) i may have had a very slight hint of backfire on decel. am i correct in assuming that this can be corrected with mixture screw adjustments.

5) i don't want to get to carried away with fine tuning right now because i'm in PA and in 4 weeks the bike and i will be in AZ where i will be trying to dial it to perfection.

Thanx a hell of alot to blastermaster for all the diagrams (i ran in and back out several times while doing the project to check things out) and to everyone else for all the input! i am learning so much from this post!!

:clap

Sorry its taken me so long to reply but to anwser you question, Nope I ran my stock needle and my stock pilot with just a 150 main and it ran fine with the stock air filter and no lid , it doesnt even compare to my Rossier Engineering pipe (that thing rips) but it ran really good

Ok, your jetting seems about right, except for the pilot jet...

1) No, the starter jet is NOT the pilot jet, they are completely different jets/terms. The Pilot jet as the diagram states controls 0(idle) - 1/4 throttle. The Starter jet which is labeled "60" on the jet controls how much gas is allowed in suring the starting process/warming up. So, as your quad is starting, the starter jet is allowing gas to flow through it. Once the quad has been started, the other jets take over from there.

2) Yes, I believe that is true. Some people call it a "pilot screw" and some call it the "Fuel" screw. It is NOT an "Air" screw. Those are only present on 2 stroke machines. Someone please correct me if I'm wrong on the whole Fuel/Pilot screw thing.

3) I'm not quite sure what you're asking here... I guess what you're saying is when trying to gain RPM's it stumbled? If this is the case, it was most likely the rev limiter since you had to clutch pulled in when revving it up.

4) Backfire is caused by lean jetting all-together. It could be the main jet, the pilot, or anything else. I would think that it's your pilot since that was the only thing that you left stock. Keep in mind, the pilot jet is NOT the same as the "fuel" screw.

5) Well, depending on the elevation of where you're staying and the conditions, you will most likely have to adjust the jetting. Who knows, you could get lucky and it could be spot-on!

About the pilot jet... I would go up to a 25. Not many people run the stock pilot with those kinds of mods.

I hope that I've answered most of your questions, if you have any more, just ask!

thanx for the reply, there won't be much (if any) altitude change from pa to AZ but the temp will prolly be 50-60 degrees warmer. it runs really well right now but i think i am lean. so i'm going to leave it alone and see what happens when i get out there. i don't see the pilot jet listed in the pics. is it there or located somewhere else? thanx again, craig.

blaster the story so far is that i live in california below 3000ft i bought a yosumura full exhaust system and k/n air filter and since this week i have had no lid on my air box and a 150 dj main jet the idel was good i took the bike out last weekend and all went well i and great exceleration through all gears and no back fires i did a plug drop and the plug was mildly sooty. this week my k/n air box lid turned up so i intall that and took the bike out to see if it was ok i live in a quiet town so i went around the block once as not to make to much noise and then did a plug drop this time my plug look more sooty than the last time and i was wondering why this would be i was expecting if anything that the bike would now be lean ans the plug looked so close last time if you was wondering yes the plug was cleaned before the last test run so looking at the facts i would say i need to drop the main jet a size. the k/n filter lid came with too jets one is a 155 and the other is a 160 they say that a stock bike no mods should use one of these above 3000ft the 160 this doe'nt seam to add up can you please help

Oops, didn't see your post! It doesn't have any info ont he other stuff because I havent had the time to add more to it.

i have grinded down my headpipe weld, and have a large endcap and no air box lid and instaled a 155main from alba racing and a 25 pilot jet and new needle and when i put the carb back on the bike wouldn't start so i took the carb off and made sure everything was in right and that there was no dirt in it or the jets and still nothing would the larger jets have anything to do with this because i tried choking it too and still nothing... can anyone pelase help me!!!!!

use uour stock main for a start

I have a 05 Z400 with Yoshi full system, k&n filter, air box lid and snorkle removed. I am running a DJ155 main and 3.5 turns out on the screw. It runs good, no backfire or stuttering. However, after reading all the talk of the pilot jet and how it controls 0-1/4 throttle. Will I have better performance if I change the pilot jet and if so what would you recommend I start with?

thanks

A 25 PJ would probably be good.

You guys need to understand that you will never get spot on jetting from other members telling you what to run. There are too many variables as far as location goes that can make your jetting way different from someone who has the same mods. Jetting is a trial and error thing... you need to mess with it yourself. I can't tell you exactly what to run when I'm all the way across the country. BTW... this wasn't directed towards anyone in particular, just making a general statement. I can give you an estimation sure, but anyone can do that. The odds of the estimation being spot on are not very good though.