XJ650J airbox alternative (not pods, not stock either).

I think you should give it a try. I've been thinking of removing the stock airbox and going for something easier to get in and out. I was podering 2 pods or 1 big air pod.

 

Hey All ... I'm WFO. Abeja's husband.

Thank you for all the helpful reminders. As you can tell, I botched the math.

Here's the goal .. what size tubing do I needt o use to make the inlet of this log-style airbox? Well, I suppose I need to at least match the stock CFM. Hmmm ... best way to do that is COPY!! Haahaa! Here's one way to think of it ....

... Imagine how long of a peice of string it would take to fit around the opening of the stock airbox (in this case it would be 9 inches long 1.25 + 3.25 + 1.25 + 3.25 = 9). To flow the same air but instead using a round shaped inlet (like what using round tubing would give us) we need a round opening that has the same circumference as the oddly shaped stock opening ... 9 inches of string fitting around the tube. So how big in diameter is that tube then (so I know what to make this thing out of)? This formula is how we come to that conclusion. I AM NO MATH WIZZZ. OBVIOUSLY!!!!!

Givens:

Stock airbox opening was guessed at about 1.25 inches by 3.25 inches (9 inches around). We need a round hole with the same circumference to flow the same air. So *pi times radius/squared* is our cornerstone if I remember right (oh god .. it's been a while and I just barely graduated from a rural high school with easy math standards).

I'm using 3.14 as pi for these figures. And rounding all figures to the nearest .01. So 3.14 x (rxr). And we need that to equal about 9 inches to equal the stock (guessed at) hole flow.

I backasswards figured it like this ....

9 divided by 3.14 = 2.86. The square root of 2.86 = 1.69 (which would be our desired radius). And finally, 1.69 x 2 = 3.38 (which would be our desired diameter .. reached at last!!!).

Sso then ...... we'd need a 3.375 tube (3-3/8ths) to feed the airbox if we're going to replace the stock rectangular/oddly shaped airbox inlet with something prefabbed and "round".

And to check the math .... (should be "pi x (rxr)" .. commonly spoken as "pie are square" .. but if memory serves it's "pi r squared" meaning pi times radius squared.)

3.38 (diameter) divided by 2 = 1.69 (that gives us radius)
1.69 x 1.69 = 2.86. (our "rxr" figure)
2.86 x 3.14 = 8.9804*** (hell, close enough .. it's 9 inch circumference).

So it came out to 9. Bingo! Right where we wanted it to be. So the math checks.

Confirmed!!!!!! ... I fuddup the math on the intake diameter equivelent. 2 inches is too small for this engine, that is IF we go by Yamaha's engineering. And THAT is a large assumption. We all know about assumptions.

In any case we had fun playing with this. If nothing else perhaps folks new to fabbing will have learned some tips on making mockups, and how to use them to gather information. After getting those intake runners all perfect in cardboard, then just cut them open and literally wrap them around the tubing you're going to use for the project and use the cardboard as a template to make the tubing cuts perfect. Welding it all together is CAKE as long as the fitup work was done with care.

In the pipe welding world (like around gas and oil pipelines) this technique is known as using a *pipe wrap*. Pipefitters pend a LOT of money on various pipe wraps for various angles and joints. So perhaps some folks can learn from Abeja's thread here on how to use wraps to make excellent joints prior to welding. Works great for making funky/custom exhaust bends as well.

Thanks for all the suggestions on the airbox design. It's just a proof of concept model. The overly squared corners and other such fancy stuff would be addressed in fabrication on the bench.

She is searching out a stock airbox. Once here, I'll dig into it's brains and see what we have. I may just copy it out of aluminum, taking the chicken way out! Haahaa! Only thing is that the 30 year old stockers are such fargin TURDS. I mean .. my log airbox can't be any more detrimental to performance than SHAFT DRIVE. Yea? I just detest plastic parts! Especially 30 year old neglected plastic parts. Just lift the seat and take a big old shyte right in the underseat area .... it would look the same. Gnarly post-enchilada dump ... right there where something beautiful could be.

Yup, turd in the punchbowl alrighty.

Anyhow .... back to the drawing board. I hope there was inspiration gathered here.

WFO (aka Abeja's old man).

 

I'm not sure I'd dis the shaft drive that quickly either. I have two similar era bikes. A 1983 GPz 750 and a 1982 Seca 750. Although they look really different, they are surprisingly similar in factory specs: exactly the same weight, five more HP on the GPz.

However, even though the GPz is chain driven and the Seca is shaft driven, the Seca is only 2 tenths slower 0-60 (4.7 as opposed to 4.5). How much of that can be attributed to the extra 5HP? The shaft really doesn't seem to hurt performance anywhere near as much as conventional wisdom would say, and it's certainly much more reliable and lower maintenance.

 

Thanx for startin this thread... great discussion!

I have a few more designs brewing in my head... it's tinkertime =)

Peace

David

 

Before you take anything OFF the Drawing Board, ... Do NOT Neglect the Importance of the Atmosphere Vent needing AIR to Supply the MAIN Air Jet and the Emulsion Tube.

Overcoming the NEED for POSITIVE Air at the Vent will go a long way toward solving the LEAN Condition.

Just installing A LARGER Main Fuel jet is NOT the Answer.
The FUEL needs to be DRAWN-OUT of the Tube.
Unless the Tube gets AIR to let flow through, up and out the Tube ... you willl NOT achieve a proper AiR-Fuel Mixture to run good.

 

Which was exatly my point .. it can't be any worse than that

(In other words there are as many naysayers for shaft bikes as there are for pods and log intakes).

It was sarcasm.

Got it now?

Mondo Cooly. 8)

WFO.

 

Quoted from another forum I'm involved with. The poster quoted is speaking directly to the use of pods (vs stock airbox) on a 1982 Yamaha XS Triple. His angle is that he believes pods can be made o run fair and well enough to satisfy most all regular Joe type riders.

(begin quote). "The throttle controls the butterfly's and these control the amount of air that can flow through the carb. The slide sits in the middle of the carb on the intake side, before the butterfly. But instead of being pulled up and down by the throttle cable as in the slide carb, it now has no direct connection to the throttle cable at all. It is now attached to a rubber diaphragm and is raised and lowered by vacuum introduced on the top side of this diaphragm through holes drilled up through the slide. The slides in Mikunis are flat.

When the butterfly valve is closed, very little air is moving in the carb bore. (The engine is getting some air and fuel through the pilot circuit.) With little to no air flowing, the air in the carb bore and the air in the closed chamber above the diaphragm are at close to the atmospheric pressure of the outside air.

Open the butterfly, and several things happen. Air now speeds through and venturi effect at the point of the slide is created. The depression at the venturi is transmitted up through the holes in the slide to the closed chamber above the diaphragm. This lowers the density of the air in that chamber. The open air below the diaphragm now wants to rush into that chamber to equalize the pressure, but it can't because there is no passage. So it does the next best thing and tries to push its way in through the underside of the diaphragm. The diaphragm can't let the air in, but it is flexible so gives way it is pushed up by the outside air pressure. As it goes up, it pulls the slide with it, and the slide pulls the tapered fuel needle up in the fuel hole. More air flows, more fuel is pushed into the air stream, and the engine accelerates or runs at higher revs.

So it needs to have a "vacuum" below the diaphragm so that fresh air can lift it to allow the needle to raise to allow more fuel.

If you fit pods alone, there is a constant fresh flow of air being pushed in, plus winds blowing in that direction. If you take apart the stock air-box........(I'll give you my one).......the air enters from behind, sucked rather than blown or forced, and goes up, across into the filter, then toward the back again, down, and then to the carbs.......kinda like an "S" shape.

Standard slide carbs, which the throttle lifts, relies on the air force to push the fuel into the chamber, so that is why they have forward facing air ducts.

Shortened..........air in the carb is initially the same as the outside pressure, the pilot circuit keeps it ticking over. Twist the throttle, the butterfly opens, the engine piston creates suction, the intake valve opens, this allows air to be "sucked" through the carb bore.........but it goes to the top of the diaphragm first, creating a "vacuum" at the bore. The air forces the slider up to allow passage to the engine piston along with the fuel from the carb. That's how I see it.

So air is not forced in, but sucked.......due to vacuum created by the engine piston and the opening of the intake valve.
This means that shutting off the air supply while in idle, or damn near shutting it off, is the way to go. When I twist the throttle I want to allow the air to be sucked in. I have come up with a design......using PODS .........on each carb, with the same amount of air to each carb, and the crankcase breather also incorporated. The air will be controlled as I twist the throttle......giving me the conditions of cv carb technology.

That's all I have to say for now on this. I had to buy my parts off fleebay, pound items, 'cos I cant get them here. I expect to get some negative remarks over this mod o' mine.......but I dont care......it will only want to make me go ahead with it more.......I certainly will not get down about it. So go on.....tell me I'm nuts........tell me something I dont already know

If at first you dont succeed.......there's always the hammer
Bobber"
(end quotes).

I'm going to try tolet all of this sink in. ~Sigh~ ... so, do the pods go back on then? I don't mind rejetting or tweaking the bank.

Abeja ...

 

When I bought my 650 maxim it had a homemade piece o shyt airbox on it. There were cracks all over it so I had to ditch it. I put on K&N pods and I have no problems. No rejetting and I even have straight pipes. I like em loud. Maybe the guys who have "issues" with pods are getting the $20 for a set of 4 crappy pods. I'm so glad I found this site, but also glad I found it AFTER I put pods on my bike. I don't think I would have spent the cash on the K&Ns if I had read the horror stories on here about my beloved pod filters.

Abeja? Did you ride the bike when it had pods on it? What did you think?

 

The Long QUOTE is Fatally Flawed.
C- / D+
He had some theory correct.

The lack of Speed and Turbulent Volume of Intake Air that is Produced by Pods FAILS to sufficiently reduce pressure at:
1) The Emulsion Tube Exit Orifice
2) Beneath the Diaphragm Piston ... Causing the Piston to lift slowly.
3) DOES Reduce Pressure at the Intake Horn's Atmosphere Vent.
a) Reducing Pressure BELOW the Diaphragm making the Diaphragm NOT Respond because the NEEDED Reductions of Pressure where such reductions are needed don't occur with required intensity.

 

I find it interesting that HESH is using K&N Pods, I have read a few things on the internet now by people using the K&N Pods haven't been seeing any problems.

The DynoJet stage 3 jet kit also recommends you use the K&N RC-1824 PODS (http://www.knfilters.com/search/product ... od=rc-1824)

Probably a stupid question as I am by far no expert but does the shape of the PODS make a difference in the situation? I notice these ones are oval and tapered.

 

Wouldn't it help even the flow to each carb if the tubing was the same size as the opening on the pods, but instead of just one large pod, run all four recommended K&N pods in line with each carb on the back side of the long crossover tube? Then the angles would be the same to each carb and maybe help out those starving interior pod conditions I read people posting about? Would that help even out the airflow ? Maybe even smaller pods if the individual carbs are drawing from all the pods since they are connected by a common source? All just theory, but maybe someone who knows what they are talking about could tweak the sizes to work?

 

There are Manifold, Plenum, Single Pod, Double Pod, PVC, Copper Tubing and Sheet Metal prototypes in the archives.

Some very creative fabricators have come and gone before you.
If you'll look in the SEARCH under PODS; you'll be amazed at some of the designs and effort that's gone into solving the dilemma.