SIMPLE MOD MAY SOLVE POD TUNING HARDSHIPS!

How did I post on this thread?

 

Guess that'll be a no then

 

Andyam5 - the airbox rubbers aren't quite "hose".... they have a bit of a contour and shaping on the inside to form the air.

I replaced my long gone ones with airbox to carb boots from a 4 wheeler that were pretty darn near close in size.

Ask any GOOD bike shop about needing suitable replacements, and see what they have. they would really just have to be the appropriate diameter to fit on the carb

Also, there is a thread on here somewhere (search for it) about a rubber PLUMBING connector that works and is dirt cheap.... haven't tried those, but it's certainly an option too....

 

Anything that is the diameter of the old airboots and smooth on the inside like the original airboots will work, along with the proper jetting and cursing of coarse. LOL

 

Thanks fellas, I'll see what I can find

 

If you are using them to run with the pods. The airbox boots for the 650's are still available from yamaha.

4H7-14453-00-00 JOINT,AIR CLNR 1

1980 XJ650G INTAKE
1981 XJ650H INTAKE
1981 XJ650LH INTAKE
1982 XJ650J INTAKE
1982 XJ650RJ INTAKE
1983 XJ650K INTAKE


Ghost

 

do you keep the jets the same size when going from air box to pod filter. I am haveing an issue with mine.

 

No.

 

anyone with pod issues, search for this in the forums," rejetting and pod air filter questions." I went by this chart, and it was a great starting point, I changed my main jets twice. After just over 2k miles on it, plugs still looking good. I used 2 stock boots, #2 & 3, and 2 fernco connectors from home depot for #1 & 4.

 

Woooooooooooohooooooooo
I've found the ultimate solution to the "POD" problem

1 Get on ebay
2 Buy a used airbox
3 Buy a new filter
4 Fit airbox to your motorcycle
5 Tear your pods assunder
6 Listen to you bike idle like a sleepy p****cat

 

Make one of these 50mm or 2inch PVC pipe and some plastic glue

 

Plumbing fernco's from any home depo or lowe's work they are 1 1/2 to 1 1/4 inches the pods fit over the 1 1/4 end.this is what I am running on my bike 85 xj 700n jets are 116 mains and 41 pilots bike runs like a champ.

 

Plumbing fernco's from any home depo or lowe's work they are 1 1/2 to 1 1/4 inches the pods fit over the 1 1/4 end.this is what I am running on my bike 85 xj 700n jets are 116 mains and 41 pilots bike runs like a champ.

 

That arrangement looks more than vaguely familiar.

That is, ... (in its basic form) ... the same configuration as an Airbox with a Filter.

A single Air Filter supplying a "Shared Volume" Plenum feeding the combined Intakes of the 4-Pack!!!

 

After reading about half of the pages in this thread I'm left wondering a few thing.
1. If you think the slide is lifting slower then why not just either drill the slide or install softer springs?
2. If the emulsion tube isn't atomizing fuel well enough due to reduced pressure in the "kidney" then why not install a larger air jet?

It seems to me a velocity stack would do 2 thing; straighten the air flow, and reduce pressure even further before the "kidney". Air reduces pressure when it speeds up.

 

Yes your right Rick. Just like the standard air box. So the moral is don't cut up or throw away you air box or you will have to make something like this when you are sick of stuffing around trying to get the bike to run right with PODS. I learnt the hard way. Having said this however, its very simple and easy to service the air filter or get the carbs off the bike when need be, with this setup. For those guys that do Bobbers and Café racers you could easily make one of these with 3 blank pods to get that Pod look and have the bike run to is optimum. like the air box system is designed to do .

 

We should therefore conclude that without being separately isolated from its adjoining carb ( 1 ) - (2) (3) - (4) ... the side-by-side, oscillations the (1)~(4) & (2)~(3) Firing Order, causes severe Turbulence at the Intake Horns.

This Turbulence, which increases exponentially as rpm's rise into the thousands, destroys the requisite SHAPE and SPEED of the AIR entering the Intake Horns.
Each carb then GULPS what AIR is present at the Horn.
Allowed to draw only from a worsening turbulent source; the Plant GULPS from this Air Supply.
There is not enough Shape and Speed to let the Carb function as it should.
There is no Accelerated COLUMN of Air speeding across the Nozzle (E-Tube) Opening, ... resulting in inadequate PRESSURE REDUCTION above the Nozzle lessening the Siphoning Effect needed to draw-up Fuel from the Main Jets.
Now, ... its LEAN.
Re-jetting is offered as a solution.
But, ... INCREASING the Jet Size only serves to make more Fuel "Available" ... to ... NOT get Siphoned and Atomized out from the Nozzles Openings.

I also theorize that the resulting turbulence also contributes to:
• Insufficient Lowering of Pressure at the small opening at the bottom of the Diaphragm Piston, ... failing to make the Piston rise as rapidly as needed.
Lean, again.
• I believe that the Volume of Air drawn-in during the Intake Stroke, if the carbs are not isolated from each other, causes a decreased pressure at the Kidney Shaped Atmosphere Vent.
I believe that without positive pressure at the Kidney Vent there is not enough Air present at that causing further complicating issues.
• Air NEEDED to surround the Diaphragm, allowing the Diaphragm to collapse, is woefully insufficient ... hindering the rise of the Piston.
• Less Air there also reduces the amount needed by the Main AIR Jets from which supply Air to the Nozzles. Hindering Siphoning and Atomization.
Increasing the AIR JET Size might not solve anything.
The AIR JET passages are only capable of a finite flow.
This is what I theorize.

It's my 2-Cents worth.
Here's a Nickel.
Keep the change.

 

In my experience with POD you can get the bike to run good some of the time but not all of the time. I tried extending the stacks etc. but what I found was in cross winds, tail winds or even strong head winds it would momentarily drop revs or bog down and regardless of how much throttle you gave it it would not go any harder. I figure that these carbs, as well as some of the other stuff Rick mentions, need an equal air pressure out side the intake across all the ventures or air intakes that's why these bikes come standard with air boxes. With out the air box to stabilize the air pressure air flowing around the individual intakes with PODS can be at different air pressure due to turbulence from the bike just moving through the air.

 

I used to do a lot of street racing Mopars back in my 20's and I used to love it when a Camaro or mustang would show up with a tunnel ram and dual quads or a single 750 on a small block. Bigger isn't necessarily better, and most people don't know that. An engine is a system as someone already stated. The key is to match all of the components so that they support each other. This means that you need to match the carb size to supply maximum CFM flow but no more. That your intake runners are the correct length for the RPM range that the engine will see, likewise the head port size, valve sizes, camshaft profile, exhaust collector length, pipe length, and muffler flow all have to match the engines displacement, desired optimized RPM. This all of course needs to be optimized for the weight of the vehicle, and it's gearing.
All things are trade offs, if you tune for peak power at high RPM then you will suffer with low RPM throttle response. That is what is happening with the pods. Engine vacuum is what give low throttle response, as it causes the carburetor to draw, and atomize the fuel. That is why on a slide carb bike, or manual secondary car carb, you get a “cough” if you open the throttle too fast. All vacuum goes away and the engine stops drawing fuel, hence why cars use accelerator pumps. What the CV in CV carbs does is maintain vacuum by only opening the slide just enough to keep the engine vacuum in the proper range for best carburetor function. It is exactly the same principal as a vacuum secondary car carb, which BTW you tune by replacing the springs on the vacuum pot.

Going back to what I know best; a Mopar 340CI small block. That motor can only flow about 600 CFM at 6500 RPM with a VE of 95%. So I ran a carter 600 on it, a larger carb would have killed low end performance. (I swapped in a 750 one time to prove this to a buddy). The stock x head already has port sizes, and valves that can flow that much air so no head work is required other than smooting the port walls and port matichg the intake (to reduce turbulence). A plain old Edelbrock performer intake also is correct for the flow and RPM range, and is a dual plane to reduce plenum, which improves low throttle response (manifold plenums only help high RPM, plenums outside the carb throat do nothing). For cams I ran 282 duration, 484 lift, 108 centerline cam retarded 3 degrees to lower the powerband. That cam actually was even a bit of overkill as it would easily pull strong past 7K. I also used a small primary long collector header and “normal” exhaust pipe with a flowmaster muffler. The car ran 12.6 with all interior, skinny tires, and a stock 3.23 rear with an 11” stall converter, if I had changed the gearing to a 3.73 I’m sure it would have come close to high 11’s. Not bad for a heavy, daily driver.

A 650CC motor can only flow roughly 90 CFM at 9000 RPM assuming an 85% volumetric efficiency which is probably optimistic on these old air cooled engines (a shop vac can pull this BTW). Four 32mm carbs can flow far more than what the engine can actually use, by removing the restriction on the intake (airbox and velocity stacks) your changing the design parameters and the expected range of the CV carbs calibration, and the engine looses vacuum, and yes you get external turbulence from the air stream. That is why it is common to put a shroud around the outboard pods.

I think you actually need to put in stronger springs to slow down the slide operation to restore the vacuum to proper levels.

You will always have to rejet to account for the increased air flow. And as I have found that all bikes benefit from at least one size larger main jet. Old bikes were designed for “real” gas, and ethanol requires a different AF ratio than gasoline, on newer bikes it is the EPA that made manufactures set them lean.

The air jet IS the restriction on that circuit NOT the carburetor passages. In order for the passages to be the restriction you would have to remove the air jet entirely.

Here is a good article discussing alot of this.
http://www.carcraft.com/techarticles/se ... ight_carb/

In summary, if you run pods and Shorty exhaust you are trading low end response for horsepower on the top end. You will never be able to “tune” back that lost response. So either don’t go to pods, or just learn to like riding a rev happy bike.

 

interesting read althomas. thanks for sharing!