Jet sizes and jetting info help

ok, now that winter is here i'm going to tear the carbs out on the xj700. it has had a flat spot from 3k-6k since i got it and they need to be gone through anyway. here's my questions. it's already got a 4-1 pipe on it and i'll be ditching the stock airbox and going with uni pod filters. what is stock jet size? any suggestions on where i should go to for jet sizes? i've done a lot of jetting/performance on my v-star so i'm familiar with the concept but don't know what actually needs to be changed on the xj. on my star i did new main jets, pilot jets, and shimmed the needles up. don't know if you do the same in these carbs or not. i know i'll need to set the mixture screws and re-synch the carbs but i'm just looking for some advise on a starting point. thanks.

also, i don't know what brand of pipe it is as it was already on the bike when i got it.

 

The stock main jet size on your bike can be found in the service manual, or the haynes manual.

As for the flat spot, it helps to know how these CV carbs work. The pilot jet controls the idle, and is controlled by the mixture screws. These will open enough to idle perfectly with your pods and exhaust.

The needle controls the mid-range (just off idle up to, say, 6k) throttle, with a some influence from the main jets. The higher the needle, the more fuel flows. Beware that needle height can be influenced by the air flow in the carb (the little air circuits that get gunked up with varnish and such), so you may be good with a cleaning.

The main jets (what you'll be replacing) mainly handle upper mid to high throttle.

I purchased a dynojet kit from mawonline.com for around $100. It was well worth it. They have instructions in for what jets to put in, and how to replace the needles. The stock needles are not adjustable, so it's handy to put in the adjustable dynojet ones.

A word of warning: it will take you more than one try to get these running right without flat spots. I recommend replacing the float bowl screws with allen head bolts so you can pull the bowls and put in different mainjets without pulling the carb rack. You will need a colortune (or exhaust analyzer). Take the dynajet instructions as a good suggestion rather than gospel truth. You may need to move things around. I personally found that raising my needles a little gave me more power in the mid range. I'm running 118 mainjets w/the needles on the 4th from the top. I'm thinking about changing to a 116 main to see what happens.

I'm also only getting 40mpg as opposed to the 52 or so I was getting before the new pods. It does run like a scared dog, though.

ON PODS: pods are finicky. They're NOT all the same, so the flow from one brand to the other may be different. This is why the jetting is more of an art than a science. If one gets somehow nastier than the others, your bike won't run as good bc it will be getting more air on one cylinder. You can pick several different types up on ebay for pretty cheap. I'm running some offbrands. No biggy. Just get some K&N oil and wash them regularly and reoil them properly. If you choose to use foam pods, JC Whitney has some from UNI that are pretty cheap. They don't flow as much air as the cotton ones, so you won't need to use as big a mainjet, but you will probably get better mpg. Remember that as you flow more, you use more . If your bike is going to be sitting outside, I would not get the foam ones b/c they will deteriorate in the sun and then get sucked into your manifold in bits. Don't ask.

Keep in mind that carbs need to be synched at throttle too. If they are only synched at idle, your flatspot may be coming from slightly out of synch throttle. Just hook up your vac gauge and open the throttle to 3500 and see if the vacs are equal.

Podding looks cool, makes the carbs much more accessible, but is a chore. Rejetting is the easy part. Tuning takes the effort.

 

thanks for the reply. nice part of this project is it sounds extremely similar to what i've done on my v-star. it's got dual cv's so i've spent plenty of time in those carbs due to pods and new pipes. from the sounds of it they're quite similar for the most part. now dyno-jet makes kits for v-star but we've found that their needles suck (for that application anyway) what we do is install M3 washers under the stock needle to raise the height. from many dyno runs it's been proven the stock needles provided a better midrange than the dynojet ones. that's why i was asking about getting the individual jets or a whole kit. but hey, i'm no XJ expert! lol. this bike is just a zip around and back and forth to work toy so i have no problem tinkering and tuning. i'm an driveability autotech by trade so i've always tuned my bikes and cars on the gas analyzer at work. way more accurate in my opinion. only thing i really need to get is the YICS tool. i've seen the pictures and plans to make one so it sounds like i'd better get going on it. how much power increase can be expected with a pod kit? on my v-star i went from 50hp stock to 69hp with pods and pipes. mostly just curious. now are these mikuni carbs in the XJ? so the main jets and the needles are the only thing in the jet kit? do you change the pilot jets? sorry for all the questions. thanks again.

 

Stock jet size is 107 main, 36.5 pilot and a 3.22/Y20 jet needle. I think Pigmouse said all rest except that velocity stacks would make the big difference with pods. Trouble is the frame tubes at the airbox get in the way.

 

Whether Mikuni or Hitachi's; to get the most enjoyment you need to have those Carbs:

Clean, "Clean-tuned" and perfectly adjusted.

Clean =
Totally cleaned. Every channel, passage, jet and fuel metering port must be wide open and totally free of any contamination of any kind.

Clean-tuned =
Function tuning. Vacuum slide pistons 100% free of Stiction and drag. Able to rise and fall with absolutely NO hesitation do to the vacuum piston cylinders being affected by tarnish and aluminum surface oxidation.

All external adjustments clean, lubed, free-turning and able to be micro-adjusted without binding. Pilot Screws loose and treated with NeverSeize. Carb Synchronizing screws lubed, "exercised' within their threaded adjuster to allow micro-adjustment without binding.

Perfectly adjusted =
Set-up for air-flow sync using the YICS Tool to isolate and adjust each one individually without the effect of the balancing supplied by the Yamaha Induction Control System passage connecting them.

Idle mixtures set using the technological advantage of viewing "The Burn" in the combustion chamber, by utilizing the "ColorTune" Spark Plug. This allows you to visually monitor the mixture's for optimum burn by observing the rich or lean color changes as the air-fuel mixture is adjusted while it's being ignited.

Once you arrive at "Carbs Tuned-up, Synchronicity and Nirvana" ... you'll understand how well engineered these bikes are; when your bike's performing perfectly and you just want to keep riding it.

 

alright, pulled the carbs today and tore them down. found some gunk in one but nothing too drastic. i'll list all the jet sizes and such i found and maybe you guys can help me get this tuned in right. also like i said, i'm GOING to put pods on and it's got a 4-1 pipe on it. before with the way it was and stock air filter setup it had a huge flat spot from about 4-7k. once you hit 7k it would wake up and take off like a scalded dog. i understand the concept of what each portion of the carb does but i'm not positive on the names of all the jets, etc. are so i'll list where they're at too in case i get the names wrong.

(under float bowls) 120 main jets, 43 pilots?
(two jets on both sides of the inlet side of the air neck) 36's
(under the needle diaphrams) 80 and 195
needle is NOT an adjustable clip style and has Y-14 on it.

any help is greatly appreciated. thanks

 

Ummm.... Looks liks somebody's jacked with your carbs before. I can't find those specs in the service manuals.

Unfortunately, I sold my XJ650 today, along with its haynes manual that would probably have the info for your bike in it.

I'm thinking you have a 700x, in which case you have mikunis, and I have zero experience with those. It appears they have more jets than the hitachis. I wouldn't feel comfy advising. Sorry.

 

mines a 700n and i just went through the xj cds and they look like the hitachi's they tore apart and cleaned. i'm getting frustrated now. wish i knew what every one else with 700n, pods, pipes, etc. was running jet wise just so i could get somewhere to start.

 

I doubt that your current setup needs more than a shiming of the jet needle. If you have 120 mains that is a big increase over stock of 107. Above 7K the engine is running off the main jets and the needle is out of the way. So poor running below that means the jet needle is back in play and starving the engine of fuel. Raise it out of the way with shims and see how things improve. If it runs well on just the main jets above 7K then they should be close to the right size. A plug shop would show if things were rich or lean. Below 7K if you open the throttle slightly and the bike runs better for a second or two then the carbs are rich. If backing off the throttle slightly makes it run better for a second or two then the carbs are lean.
Also the jet in the center of the carb body after removing the float bowl is the main jet. The jet close to the side of the carb is the pilot jet. The jet needle is the long tapered needle attached to the diaphraghm. The needle jet or better called the emulsion tube is the long brass tube with small holes in it's side that the main jet screws into and is removed from the top after removing the diaphraghms. All others are air jets and do not need to be removed to properly clean the carbs.

 

now we're talking! thanks for the big help. i just didn't know if i needed to mess with the air jets or compensation jets at all. in that case... i should be able to easily get it dialed in. yeah, above 7k this thing pulls freakishly hard. if i can get it to pull like that throughout the rpm band i'll be set. since i posted the first post i've gone through all the carb diagrams on the xj cd's and got all my jet locations and names down. probably should have done that first.. lol. couple quick questions.... now it says stock needles should be a y-14, i've got y-20's in mine... do you know the difference? it's an M4 washer right to shim with right? and stock pilot jets are 36.5's and i've got 43's. do those sound about right for the pods and pipe? the bike never ran very well in idle to 3k range (inconsistant idle, popping, etc.), and i've got the mixture screws at about 2.75 turns but seeing now that these carbs have been seriously messed with by someone i have no doubt they're probably WAY WAY out of synch. i know everything is good and clean at least now. i knew i had to do that before i did anything.

 

Yes I have heard that the M4 washer is correct, however I have not built carbs in way other way than stock. Pigmouse has and can answer with authority.The difference between a Y14 and Y20 being the diameter. Some manufactures will also change the taper. Where did you get your info off the XJCD? I found a stock jet of Y20 not Y14.
The rough idle makes me want to colortune to see what is happening. The only way to know other than a dyno run. A 43 pilot doesn't sound too far off but a colortune is the only way to be sure. I would first try to get things dialed in with your current setup before throwing in the added problem of pods. Many here have tried pods only to abandon them in the end. The idle circuit can affect response up to about 4500 RPM, So dialing this in correctly may make a great difference. I therefore strongly advise setting this before anything else. If the popping you hear at idle is through the carbs then one or more idle mixture screws is lean. I have run into this at carb clinics many times. It absolutely kills throttle response.

 

i easily could be wrong about the needle size. i think it's definitely time to get a colortune if i'm gonna keep going with this. this is just a rip around fun bike so i'm not concerned with the excessive amount of tuning with the pods. i'm more interested in the power increase. i'll look into the colortune thing and start working on making a ycis tool today. i'm sure with those two the whole project will be a lot easier. i'll probably grab some washers while i'm in town today as well. thanks a lot for your help.

~nick

 

I have a set of carbs her at home that I am rebuilding and based on it's needle an M4 washer will work just fine. Colortune plugs are available from Morgan here: http://www.carbtune.com/colortune.html and someone found them stateside at eastwood.com. If oney is an issue right now at Xmas time, the Morgan link allows you to buy just the plug for about $36 USD. Click on the order link to get to that offer.

 

sweet, thanks for the info. i'll definitely be getting one soon!

 

northerntool.com has em as well.
shipping is reasonable

 

success!! just wanted to let everyone know i've (for the most part) got the bike dialed in. added one m4 washer to the needles, cleaned the carbs, built the yics tool and synched the carbs, screws at 3 turns out and it runs like a maniac now. very powerful all throughout the rpm range with no hesitation or flat spots. idles rock solid and overall runs great. colortune plug is on the way so when i get that i'll finally get it "perfect" but for now it's amazing how much better it is. thanks to everyone for the help. i really appreciate it.

~nick

 

Allright!!!! That's what I like to hear! Looks like we were right about the neddle just needing a washer. Are you still going to put the pods on?

 

Post your Dialed-in set-up with all your Mods and adjustments.
There's likely to be some people that want to do the Mod's, too ... but, are waiting for the right combination of pipes, pods and jets.

Pipes:
Kit:
Intakes: (Pods?)
Main Jets:
Low Speed:
Pilot Screws:
Vaccum Piston Needle:
Other:

Something like this. The Thread should be something like: "Pipes, Mods and Special Tuning Set-up"

 

absolutely! don't want to miss out on that power increase.

 

i definitely will. i'm waiting on the actual filters to show up any day so once i get them i'll get it completely dialed in then post the results. i want to make sure it's dialed in perfectly so i don't mislead someone.

 

I just bought a 12mm (for my honda) on ebay(etoolcart) for around 69 bucks shipped and everything. Mine has something wrong with it. Apparently, Gunson changed their design with the new motorcycle version. I checked and found that the lead that you screw into the plug has no continuity . Sending it back tomorrow. You need a 14mm for the xj.

Sorry I wasn't too helpful earlier. I was thrown by your numbers and what I found in the service manuals... Here's a stab.

On my 650j, I was running pods and 4-1 with the stock pilot jet. I used the Dynajet needles, so I don't know what the diameter difference was. I just threw them in and later played with the clip heights. I would suggest trying one washer, then two. You may need to raise that bad boy quite a bit, but do it in small increments until you like it. The changed needle kinda makes me hesitant, but you should be ok.

I would suggest you get your idle right before you go messing with the needles, though. There is a small influence just off idle there.

Mains: I was running a 118 with pods/header. The stock size on a 650 is 110. Hopefully, that will give you an idea of the size difference.

Pilot: I'm not really sure how to compensate for the larger than stock pilot. I would think you'd be able to adjust it out correctly once you get your colortune. You may have to go back to stock pilot jets, but I doubt it.

SLIDES: This is important. There are two holes in the slides for air to pass through. This air flow determines the lift rate of the slides. The Dynajet kit come with a drill bit to drill these holes out to correct size. I will check to see what bit I have for the 650, as I still have the kit. These holes need to be drilled out in order to acheive the power throughout throttle that you are looking for.
Shoot me an email, as I do not get on this board very much lately. I would be glad to mail you the bit as long as you mail it back to me. (of course if it's a simple size, I'll just tell you what it is when you email and you can grab one out of your bit case!) desertpigmouse@yahoo.com

 

You can measure the diameter of the shank on the drill bit. That value will tell you what number drill it is.

 

thanks for all the input, i'm extremely close where i'm at right now with adding the shim to the needles, synching and cleaning the carbs, and bringing the mix screws out to 3 turns. bike starts great when it's cold, idles rock solid, and screams throughout the rpm band with no hesitations anywhere. if weather cooperates i'll ride it to work tomorrow and throw it on the gas analyzer at the end of the day just for some confirmation. only thing i might do is drill out to one size larer on the mains. gut feeling says i can get a little more up top.

 

how's this for a curveball....... got the filters on and some decent weather today and got to go for more than a 5min ride. bike seemed a little doggy down low, very strong in the midrange and a little lean up top. i was baffled by this as i really figured the 120's would be large enough and before i added the shims it "felt" like i was good in the mains. slid into work and threw in on the gas analyzer and confirmed i was still lean at 3 turns out. now i'm really baffled by now since i know i shouldn't be any farther out than that and i really figured the 43 pilots were plenty big compared to the 36's stock. so, frustrated i went home and pulled up the xj cd's just to look at the exploded diagrams. now from the beginning i found it really weird that it had a y14 needle in it since it's suppose to have a y20 but i sortof had forgotten about it since it ran good in the midrange. then i stumbled upon the answer to all my problems. it's a freakin 750!!!!!! i ran the number on the engine and it came up with an 83 xj750ml. someone stuck a 750 and the carbs in the xj700n frame! sure enough.... carb diagrams for the 750ml came up with the exact jet, needle, air jet, etc. numbers that i've got in there. sooo..... end result was that originally with the pipe and pods i was lean all around, but REALLY lean in the middle. so when i added the shim it brought the middle into play but then showed the true colors of the top and bottom end being lean. making sense? lol. what a pain in the butt! at least now i know though. so, tomorrow i'm gonna grab the jet drill bits from work and do a little drilling on the pilots and mains. at least now i don't feel like a complete idiot. just goes to show when you buy something used you never know what you're getting!

 

just in case you didn't see it, take a look at my last post. how about that? lol.

 

Not sure if this is relevant but on the XS forum a common problem with putting pods on is some pod designs actually cover the air jet with the lip inside the pods. worth having a check at the pod design before you go drilling out jets.

Let me know if you think it's a problem and I'll find a link for a workaround.

 

i'm pretty sure they're not even close to blocking them but i'll take a look tonight for sure. thanks for the heads up.

 

Hey pigmouse, do you know the exact part number for the jet kit that you bought?