Pods. Tuning Option For Those Who Are Still Too Rich!

Ripping a page right out of the NASCAR Tuning Regulations and what Inspectors look for to discourage cheating; I think "Restrictor Plate Racing" can be applied to XJ-Bike Tuning and be beneficial in the endless search for "The Solution" to getting Dialed-in running Air Pods.

I think the "Too much AIR" problem has a solution.

The McKey Perforating Company manufactures sheets of "Perforated Stock Material" with a wide variety of patterns and **Percent of Open Area** that those of you who are experimenting with Pods should investigate.

Not only does the McKey Company have perforated stock in various percentages of open space. They have the capability to PRODUCE a CUSTOM Sheet to specifications needing: More or Less Open Area ...
Patterns to solve percentage issues ... and, choices of Materials the Perforated Product will be made from.

McKey Perforated Products Inc.

http://www.mckey.com/docs/products/perfstock.htm

 

So let me get this straight: Somebody installs pods to increase the intake flow. Then they use restriction of some form (like the material you suggest) to DECREASE said airflow to get the carbs to work right.

You suppose with the right restrictive material choice it will flow the same as the original airbox?

THERE'S an improvement... Darn, Rick I don't know why nobody thought of that sooner.

 

Some people get pods just for looks. (and it's too lean)

I think there could be some gains by switching to the other kind of carb- - the ones that the throttle IS the slider. But that still means adapting, tuning, and experimenting.

 

I also think there's an attraction to the ease of installing-removing the carbs when you have pods as opposed to the stock air box and boots. Personally I don't think their worth the hassle but what do I know? Also when you remove the stock air box you have all that room for a small luggage compartment. What do people put in that space upon removal of the air box anyway?

 

There was an old post on here where someone was talking about experimenting with wads of foam inside the pods until he got the airflow down to the level of a stock airbox setup. It was an older post that I stumbled on to, I don't think the guy ever posted his results though.

 

Maybe that guy is too busy with the chicks he picked up from having a more muscly bike.... or maybe he's stranded somewhere in the desert from them.

 

OK, let's say you came up with a cone shaped piece that Fitz inside the Pod. You make 4 identical cones.
It has exactly 60 holes. You run it, and it's still too lean. You tape over 5 holes and see a slight improvement. You tape over 5 more holes and see black plugs. Now it's easy- - you are tuning in a range of just 4 holes. You could even tape over half a hole, or have 8 holes blocked on one pod, 6 on another.

I see where this would work. But there would be no need for a custom sheet of material, unless you went into high volume production of a finished product. Everybody would still need to fine-tune these screens to their particular exhaust/bike/set-up. The final cone would need more holes than needed for the final tuning.

And it's all just theory until someone gets out in the garage with some tin snips and RTV cement. (and beer).

 

I was debating pods on my XS400 because the stock air filters are hideously expensive... and soon, I imagine, impossible to find.

The question I have is, does this perf material flow the same CFM at all RPMs as the stock airbox? I mean, you might dial it in for idle, but at WOT/redline it might be more restrictive than the stock airbox since for the same total open area, a lot of small holes flow less air than one big hole. I think.

 

its all about harmonics, and a restrictor plate is a narrow rpm range bandage. jet and tune your carbs correctly. its not impossible.

 

I don't think Harmonics is the right word to use to describe what is needed and not provided by Air Pods. Harmonics is frequency.
(But, then ... you will be pulling-off your Carbs with greater frequency!)

The problems to overcome running Pods on Vacuum Carbs are many.

Vacuum Carbs are NOT designed to accommodate Pods.
Pods eliminate the Air Boots which are the racks Velocity Stacks.
The Total Volume of Intake Air is shared by the 4 Carbs,
Cubic Feet per Minute is Precisely Regulated by the Airbox Inlet.
Pods do not regulate Intake Air.
Intake Air is not Velocity Stack Shaped and nor its Velocity Increased.
The element of Turbulence is introduced by the Pods.
Unshaped, turbulent Intake Air fails to sufficiently lower pressure above the Emulsion Tube Outlet causing insufficient amounts of Fuel to enter the Intake Air Stream causing a Lean condition to occur which is not addressed by installation of a Larger Main FUEL Jet.
The Incoming volume of AIR >> remains insufficiently "Shaped", turbulent, and of Insufficient Velocity above the Emulsion Tube opening to provide the dramatic change in pressure above the E-Tube to effectively aspirate the Fuel from the cavity.

Manifold Vacuum causes the Diaphragm Pistons to rise allowing copious amounts of Air with insufficiently Aspirated and Atomized Main Jet Supplied Fuel supplied to allow the Engine to develop power.

For Pods to work ... they are going to need to be integrated.
The Pod needs to Restrict the Volume of Air.
The Air entering the Pod would need to be Shaped and Directed.
A Venturi-type "Insert" needs to direct a condensed flow of the Air across the top of the Emulsion Tube.

It's not Harmonics.
It's Aerodynamics.

 

rick, its the difference between a 1' pipe and a 10' pipe. the stock airbox doesnt restrict flow until the upper revs, if it does at all. it does change the reciprocating velocity (harmonics) of the air coming into the carbs throughout the rpms when compared to an open element design.

an airbox or manifold type intake has harmonics involved. an open element has dead air with no music to change the air charge at the carb inlet.

if your restrictor plate theory is correct, someone could throw dirt on their pods and call it a day. it may bandage a symptom, but its not fixing the problem....incorrect jetting/carb tuning.

 

Wow.

 

You're both right. It's both, as is the exhaust system ("backpressure" is a myth.) 8O

*ding*ding*ding* Bob, tell that man what he's won!

If you switch to good old MANUALLY controlled carbs then tuning for pods is not an issue. It's these damn vacuum-controlled CVs that have to live in such a controlled environment to work; they're only on there because we, mere mortal humans, do not have the ability to control our right wrist in an EPA-satisfying manner.

NOR do a lot of us have the knack for throttle control on a motor with an effective 8000 rpm "working" range. With slide-valve carbs you have to apply throttle as the revs rise, simply slamming it wide open will bog the motor. With a wide-band motor such as the XJ, it would make the bike unrideable for most consumers. With CV carbs, Joe Average can grab a big handful and the bike will respond, because the carbs will take over and apply the proper amount of slide lift AS THE MANIFOLD VACUUM RISES.

The first thing serious racers do is ditch the CVs for slide-valve carbs. But we (mostly) ride on the street.

 

So if manifold vacuum isn't lifting the slides enough, can't we put weaker piston springs in?

 

If you have a spare set of piston springs, you can cut the exact amount of coil off of them so they would be the same, and lift the slider and needle the same added amount. Keep the stock springs just in case.

Zookie400, you would have to throw the exact same amount of dirt on each pod. . . :lol:

So, has anyone with pods added a few inches of "runner" yet?
This added velocity stack may address a couple issues of turbulence and some air volume.
Or maybe nobody wants to complicate the simplicity of pods.

 

I was thinking about doing this for a while before I even read this post. I have a extra set of carbs that I would like to play with for my pods aplication. As far as restrictor plates go I was going to do something a bit different, but it would still restrict the amount of air flow into the carbs but also reduce turbulence.

My idea (and I know most of you are going to laugh or spit at it)
was to fab a cone type sleeve (like a funnel) that would slip on each carb. I would of course have to have each of these cones flow benched until I get the desired amount of cfm's of airflow through them.

First I would need to know what would be ideal flow for these carbs.

In my case I only want to go with pods to clean things up.

 

At that point, it would be easier to just put a rack of standard carbs on it and tune them.

 

What exactly are standard carbs for these bikes? Are there any that bolt right up?

 

Sort of. You would want a Mikuni or Keihin slide-valve carb in the same "size" (intake throat dia.) as your bike; and they would have to be mounted to an adjustable "rack" to fit.

The biggest drawback (and why this isn't a commonly discussed solution) is the high COST (up to $800/ea new) for such carbs. That's why more of us aren't running slide-valve carbs. I had looked for a set for my 550 (since they were often raced) and they're out there but I didn't want to spend upwards of $2K for a used set, and still have a tuning challenge ahead.

 

Could adjusting the Air/Fuel mix screw compensate for any rich/lean conditions?...

I have a LM1 wideband 02 sensor I use to tune cars with, and I thought of taking off the muffler/mid pipe to expose the header collector so I can put the wideband 02 sensor inside each exhaust runner to read the true air/fuel mixture from each cylinder. Then using the air/fuel mix screw to adjust a little? if the fuel mix is way off I have dynojet stage 1&3 jets to play with, 120, 124, 132, 136 main jets.

I ride a 82 XJ750 Maxim, 4-1 header/exhaust, K&N box air filter and stage 1 dynojet kit 124 main jets.

Is the wideband idea worth trying?