Stupid carb question

Are all mikuni carbs slide? Or should i be looking for a specific one to work on my xj650. Thinking about switching to mikunis to solve the pod vs cv issues.

The way i see it either solution will cost $$. Fabricating a carb intake baffel to slow down the air or buying a carb that works with pods.

 

no
even if you have round/flat slide carbs your pod problem isn't completely solved. at slower speeds it might work fine but at higher speeds the outboard carbs see air going by real fast and the inboard ones are in a pocket of air behind the cylinders, that's going to change the mixture from high to low speed for each carb. getting caught in the rain is going to clog the outer pods but not the inners so much.
i read a test of a new 750 kawasaki, one if their new features was a new 17 liter air box, engines like a stable air supply, pods are about as radical as there is.
might as well live with what you have

 

Pods are not worth the trouble period.This is not a small block chevy where putting an open element filter help the engine to breath. A stock air filter keeps crud out of your engine , pods are not as efficent and riding in the rain is a big problem .

 

This is a very bad idea............

 

Stupid phone.

 

At this point i cant go back to an air box. Too many modifications. If the main issue with pods is air/vacume wouldnt creating a slip over cylinder like baffel to control the amount and turbulence of the air flow solve the issue on a cv carb?

Depending on the pod eg uni pods you can even slip in an interior rain guard that channels the water away from the baffel opening.

 

The analogy i keep thinking of is cv + airbox is like sucking soda through a straw while a pod is like having soda poured right into your mouth. At first its fine, as the volume increase you choke.

 

one member made the claim that covering the side of the carbs eliminated the wind air problem he lefthis side covers on which covered the pods.
air box keeps a uniform air flow to all carbs with the carb boots serving as velocity stacks.

your analogy is incorrect. with pods you do not build up enough vacuum to lift the slides in the carb to allow air to flow through carb throat and fuel to flow through the main jet into the flow of air.

 

if you were to take a pod apart and measure the area of filter medium, then do the same to a air box type filter i think you would find the air box has way more area. so is there more flow through a pod or air box? remember the carbs draw individually not all at once. the pod engine might be running rich at mid/full rpm's

maybe the opposite is true or since air can stretch and compress, the short distance from the restriction(filter)to the slide has something to do with it. increasing the distance with the intake side tube seems to help some guys

 

you could go to non CV carbs but then you would have 4 throttle cables to adjust.
in a recent post a member made an intake manifold box for 2 cylinders, with just 2 carbs one for each bank

 

From everything i read and tried to learn about our air boxes, and air boxes in general is that they are there to help supply the engine with x-volumn of non turbulent air.

Please correct me if i am wrong. I am still new at this.

The vacume created by the engine sucks the air through the carbs. The air box normalizes the air that passes through the filter and then sucked into the carbs via rubber connections that act like velocity stacks. The velocity stacks conforms the air to flow through the carbs with minimal turbulence.

If that is correct, why cant an insert or a restricted velocity stack work?

 

I just want add before its pointed out. The box also creates air pressure to move the diaphragms. With pods the turbulent air doesnt create the necessary atmospheric conditions to make everything work properly.

But....

If there is a way to create this within a pods aka mini air box. Then pods work.

 

interconnecting the pods would be a step in the right direction, as well as controling available air flow into the pods.

you would be better off with the dual filter set up made by K&N to start with

 

. . . interconnecting the pods (like putting them in a box) . . .

 

if any thing I am subtle


sybe
if you are going to run pods just find your flat spot and tune the carbs to where you can live with it

 

Bingo! the only way to make the same air flow at the carbs is to use a airbox. Let's say you're too lean at mid/high end, a main jet can change high end but only a little of the midrange. Shims can change WHEN the mixture changes in relation to the slide but not HOW MUCH. If you have a 650, maybe 750 needles could help the how much part. ?
There are no richer needles or needle jets for these carbs that i know about. The only way i see to make the mid/high end richer is to modify the needle jets.
It would be a long dark road but maybe a guy could drill out the little holes on the sides of the needle jet (on a set of spare jets ) To make the mix richer as the slide goes up.
That's a lot of work, but i don't think i've read about anyone trying it.
If i ever lose my mind and go to pods, that's what i would try.

 

If one was patient enough, they could start swapping main jet needles and test the results:

Original main needle size configurations are as follows:

Y-10: used on all USA market XJ650 (except Turbo) models, 1982-84 XJ650 Canadian bikes, and 1982 XJ650 Euro (model 14R) carbs.

Y-11: used on all 1980-81 XJ650 Euro (model 4K0 and 4K1) and XJ650 Police (37G) carbs.

Y-12: used on all Canadian 1980-81 XJ650 Maxim, Midnight Maxim, and Canadian 1982 XJ650RJC Seca (non-yics) models.

Y-13: used on all USA market XJ750 (1981-83) models.

Y-14: used on all non-USA market XJ750 (1981-84, except XJ750RL) models and XJ750 Police (24L and 37H) models.

Y-17: used on all XJ750E-II models.

Y-18: used on all XJ750RL Seca models (1984) only.

Y-20: used on all XJ700 air-cooled models.

others: all other Y-xx size needles are used on other model Hitachi HSC series carbs, such as XV750, XV920, etc. models.


Original main needle size characteristics:

As noted previously, as long as all four needles are the same between all the carbs on your engine, you can swap around different sizes for "tuning" purposes. Although we have no guidelines nor experience available to assist you in your tuning exercises, we can offer these needle shape characteristics to help you in analyzing your needs. Be aware that the thickness of the needle at any position along its length determines the fuel flow through the main fuel circuit, and the rate of change of the needle thickness (the "taper" amount) determines when and how much the needle allows the fuel mixture to become leaner or richer.

- the Y-20 needles (XJ700 models) are "skinnier" at the bottom of their shaft than either the Y-13 (XJ750) or the Y-10 needles (XJ650). Thus the Y-20 needles are "richer" at higher rpm ranges than either the Y-10 or Y-13 needles.

- the Y-10 needles (XJ650 models) are "skinnier" at the bottom of their shaft than either the XJ750 Y-13 or Y-14 needles. Thus the Y-10 needles are "richer" than either the Y-13 or Y-14 needles, although the Y-20 (XJ700) needles are even richer, but only at wide-open throttle positions.

- the Y-11 needles (XJ650 Euro) are a bit leaner than Y-10 all the way through the rpm (needle position) range, especially at wide-open-throttle position. They are a bit richer than Y-13 needles, except at the wide-open-throttle position.

- the Y-13 needles (USA XJ750) are "richer" than the Y-20 needles (XJ700) throughout the rest of their overall length.

- the Y-14 needles (non-USA XJ750) are "richer" than the Y-13 needles (USA market XJ750) at 3/4-throttle positions and beyond; otherwise, almost identical to the Y-13 needle.

- the HCP20965 needles (custom) are the "richest" at all throttle positions except for the wide-open-throttle position characteristics of the Y-20 needles (XJ700).

- Summary: of all the stock needles, the Y-10 (XJ650) needles are, except for their lowest section, the "richest" stock needles available. The Y-20 (XJ700) needles are the "richest" needles available for their lowest section, but then quickly become the "leanest" needles past their lowest 1/3 range of length. The HCP20965 needles are the richest needles available at all throttle positions overall, and people who are running pods and other modifications on XJ700 and XJ750 engines may wish to keep this thought in mind when trying to tune their engines.


One last thought: remember than fuel system tuning is mostly an art, rather than a science. The different size needles can produce very differing characteristics on any given engine, not only due to their relative "richness" or "leaness" characteristics, but also their rate of richness or leaness at any given needle position, along with the differences in main fuel jet sizing.

 

Wow that's good stuff but too much for me to digest with half a hangover
any insight on the needle jets that the needle goes into?
maybe some combination of needles and jets could lay this to rest

 

I seem to remember seeing pictures of a member's bobber that had a single pod filter and a manifold made from pvc or abs pipe. Anyone remember who that was and if it worked out at all?

 

u are

I think he also had a single carb.
many things have been tried

 

It's never too early to start drinking! Jack Daniels: the Breakfast of Champions.

On Hitachi carbs, there are only two different main needle jets (a/k/a emulsion tubes): HSC32 version and HSC33 version. But, I can discern no meaningful differences between the two in size, shape, # of air bleed holes, size of air bleed holes, etc.

Perhaps you could be a test mule?

 

I am loving this conversation! So thank you guys for participating.

I believe i still have spare plungers and needle jets so I don't mind hacking them up. My only hesitation is that we would still be introducing turbulent and sporadic air into the carb. If a large guest of wind from behind or from the sides or even during a turn hits the carbs just right, it will rise the plungers sending more fuel. This might be me over thinking it like i always do.

Here is a rough sketch of something i was thinking about making that might solve the problem.

 

The one I'm remembering was four carbs and he made a PVC manifold connecting all the carbs and had either one pod turned forward or one pod on each side turned forward. It took up less space than the airbox and looked quite nice, I just have no idea if it worked out for him.

 

sybe
this link is on how to tune the carbs with rejeting
it includes work on slide needles , this is where you would follow chacals information.
it gives the proper order to work on the carb
http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html

I belive factory pro makes carb kits

 

you dont believe its an air flow issue that can be solved at the pods?

 

no thank you sir, i'm emotionally attached to my airbox and its fuzzy little filter

 

Yamaha engineers would have put pods on if it were the best way to go for the cv carb.

you8 need uniformity to make 4 cv carbs work together.

i air filter will always supply the same air flow to carbs from first install to just before you replace it because it is dirty.

with pods you have 4 air filters with subjective exposure to the elements .
that 1st splash of the puddle that sends dirt into the outside carb changes its air flow only.
same with the dust cloud blowing across the parking lot.
in a nut shell an air box removes variables.

you may solve the issue using pods it would work well on the drag strip or race way because you would change out the pods with every week end race or just use velocity stacks

i think chacal is onto something with the slide needles .

I will say if you can develop a pod system for the xj you will become rich , as there are many companies out there selling jet kits for the modifier's of xj and many have tried. only one person claims sucess on this site and that involved leaving the sidecovers on ( for the cross winds)and he never rode the bike stock.
you can make the bike rideable and reliable with pods but it is unlikely you will get better throttle response results than Yamaha

 

One thing that's being overlooked in this discussion about air boxes is the effect of the pulsing of air as the valves close. There is a rebound effect, which partially pressurizes the incoming air charge for the cylinder that is about to be on the intake sroke. It's a small thing, but a ncessary part of an engine bing able to run well (efficiently producing power) with relatively large amounts of valve overlap (as most all engines have run since the early 80's).

Even when getting an engine to run well with pods and CV carbs, you're giving up power and efficiency.
Think about that for a while.
Building a sporty machine that makes less power.
Hmmm.....

 

The debate over air box and pods is moot. We can all agree the air box is headache free, easiest to make work and prolly the best the factory could tune.

What i am doing is trying to find a workable solution at the intake/pod side to make pods work. I know its possible. I just need to figuere out the air flow issue.

The key is creating a stabalized environment inside the pod. Gills inside the pods, restrictors, tubes connecting 1 to 2 and 3 to 4,
It can also be so simple as just internalizing the beer can mod with a membrain or water trap.

I would like to poke the great minds of xjbikes to help and brain storm for a possible solution.

 

Carbs with cable-operated slides.
Keihins run around $150 each without jets. There was a place offering a whole set up, jetted and ready to go, intake adapters, mounts, and cables, for around $1200.
Ther are other options of course, but all will require fiddling.

 

I've seen these looking at cb750s, I don't know how well they work, or how/ if they could be made to fit onto xj carbs, but they seem interesting:
http://www.steeldragonperformance.com/air_boxes_7.html

 

have you ridden it yet with pods? just to see what it does or doesn't do. when i messed with air filters and exhaust, i took the same route every time and took notes.
it's easy to remember one ride ago but not two or three. if you're looking for rich or leaner, it's easy to go past what your looking for. you need small steps and only make one change at a time.
I'd start with the richest needles from chacals post and go from there. you can change needles without pulling the carbs

 

If you do not interconnect the pods,I think you need to make the individual pod restriction equal the air filter restriction

this is a great discription of what an air box does and what you have to replacate to get pods to work.
From a post byKmoe

Pods really aren't for max airflow though. They look like they should flow more air, but in practice they don't always. The XJ airbox is realtively restrictive, but the advantages from the waveforms generated in the airbox overcome that restriction. In addition to providing the airflow necessary to allow the carb slides to move properly (and quiet intake noise), the airbox also uses the resonance developed from the "blowback" of the cylinders (a consequence of valve overlap) to force-feed a little more air through the one carb that is working on the intake stroke. With individual filters that free-supercharger (as Kevin Cameron calls it) deos not exist.
Have a look at what a modern aribox looks like on a sportsbike. They are huge, and have many different shapes within to further tune the resonance for maximum effect in the midrange (exactly where we see pods cause a flat-spot in our XJs). This is done even on (most) fuel injected race bikes, where one would think that pods would have an advantage without causing any fueling issues.

 

Can you link to that post? Sounds kinda cool.

 

I dont think anyone tried it cause its easier to change the needle than to drill out the holes. the needle jet controls about 10 - 60% of open throttle while the needle is about 20 - 80%. Since the loss in power is typically in the mid range and if your theory is correct i would only need to increase 1 - 4 holes.

 

Then again no one really confirmed if the engine bogs down due to flooding or just not enough air flow.

 

That a very good and useful diagram Sybe, where did you get it from?

 

Gotta love google! it has helped me find some nice nuggets of information about possible solutions.

 

if those sizes in the picture are for a Hitachi carb?
a #70 drill bit is where i'd start
http://www.mcmaster.com/#2901A247

 

It bogs from being lean because the slides can't rise enough to meet the engine demand for fuel.

 

would drilling larger holes or more in the main needle jet tube make the fuel leaner?



the main needle JET
power valve
emulsion tube

 

I also thought at first running lean would produce more torque cause of the higher revs and the bog was from less air to ignite the fuel.

how ever the issue is definitely at the needle, there are just different ways to attack it. find a way to generate low pressure air to raise the diaphragm, change the needle size, or try increasing the needle jet holes.

 

if you could increase the range of the pilot jet circuit it may help increase the vacuum to lift the slide

if the pod had same air intake opening square inches as the airbox would also be a good start




from
TALKIN' TECH: Various thoughts on various issues

The pilot fuel circuit is active from idle up to about 2500-3500 rpms, and at about 3000 rpms the main fuel circuit starts becoming involved, and by 4000+ rpms the main fuel circuit is responsible for about 80%+ of the engine's fuel supply conditions.

 

I have to take a step back from this. Lastnight i decide to pull the motor for painting and while draining the oil an excessive amount of silverish oil came out. Which lead me to pulling the oil pan and well... there is aloy of metal, aluminum flakes and part of a piston ring...

The ring might be part of an one that broke when i put new ones on. Which is scaring me there migbt be major internal damage

 

Not sure what thise small black pieces are. Its not plastic and they are curved

 

The solution lies with playing with the slide spring and the air jets. Same thing that Hitachi did when they set the carbs up for the Yamaha 650/750 engine.

Sutch a hassle though. I'd rather go riding.

 

Woohoo rings are fine! Compression is at 150 for all 4.

 

Wow..
That was a great read, and very informative!
I have pods on my bike, they were on it when I bought it. It had "dial a jets" jammed into the pods.. I couldn't figure out why he didn't just rejet the carbs??
I'm starting to pick up on it now...

 

Never heard of it, but it seems interesting. did he drill holes into the carb body to mount them?

 

No, he had them jammed in the boot of the pods.
Guys who snowmobile in high altitudes use them to avoid leaning out on their decent.
Putting them on a bike seems lazy to me though.. lol