For Pod Guys & PVC Manifold Guys ONLY !! By: Rick Massey

The Diaphragm is sealed from any other influence upon it when the Carb Top is on tight and the Rubber secured in the edge lip channel.

The VELOCITY of the Intake Stream over the HOLE at the Bottom of the Piston causes a Pressure Differential upon that small opening at the bottom of the Piston.

The AIR JETS are isolated from the Vacuum Chamber.

 

I am going to throw my 2 cents in here. What the air box has over pods is it gives a bit more restriction so you have a bit more suction on the hole that activates the diaphragm. Which raises it faster plus the intake just doesn't suck the overlap in the cam actually blows the fuel mixture back towards the carburator wich also enrichens the mixture and helps it atomize. When you drill out the hole you get vacuum to the diaphram quicker so it opens faster so you need bigger jets to supply the fuel. I have not seen it on hitachis but on Mikuni flat slides they give you lighter diaphram springs to accomplish this which means it opens fully at lower rpm. The bigger hole helps with pods. When TNT did my carbs it took 28 dyno runs to dial it in right. They get the slides dialed in with the right springs then they work with the jetting and air bleeds to fine tune it. Any tuner will tell you slow speed small throttle openings are effected there is no way to get it right. The funny part about my v max it made more power with stock air box with a drop in k@n and the lid off over pods but it had adjustable v boost which connects all 4 carbs turns it into 1 4 barrel
For the gear heads that mess with hot rods have you ever changed the diaphragm springs in a vac secondary holley carb the lighter the spring the faster the butterflies open which leans out the mixture and doesn't pull as well down low but catches up at higher rpm
Every bike i have ever messed with with cv carbs you can jet it for the extra air from pods but just jetting doesn't do it there are a lot of variables slide speed needle jets all work together. Dont get me wrong pods can work ok with just some jetting but takes a lot of time to get them near perfect. There is a lot less variables with an old slide carb because you control the amount of movement with the slide. One thing i forgot to mention look down the throat of a cv carb when its running give it a little gas you can see the slide bobbing up and down with the intake pulses.

 

Re: For Pod Guys & PVC Manifold Guys ONLY !! By: Rick Masse

Most loss of vacuum problems associated with pods can be overcome by enlarging the hole in the slide to amplify the signal going to the diaphragm to raise the slide. There are specific instructions in Dynojet kits on how to do this, and how big to make the hole. There may be some merit in reducing the effect of the engine vacuum on the vent port to make the slide rise easier, however, limiting the size of this port seems like a bad idea, unless you want your slide hanging up when you close the throttle. Air has to get out when the slide rises, but it also has to get back in when the slide falls. It is probably supplied filtered air to keep crud out as well, which would definitely interfere with proper diaphragm and slide operation.

As far as PVC manifolds go, it seems the carb farthest from the opening would have quite a strong vacuum signal due to the air being sucked up by the three carbs in front of it having to be replenished along the full length of the intake runner, while the carb closest to the pod would be suffering the typical pod breathlessness. This may all be theoretical rather than real-world issues, as I don't have any experience with making my own airboxes or intake runners. I would tend to want a filter on each end of an intake just to balance things out, or, as others have suggested, one or two pods centrally located in the plenum, or between carbs 1 and 2, 3 and 4.

As far as my earlier statement about this port supplying vacuum to raise the slide, it does do this on other carbs, such as the BST36SS Bandit slingshot carbs I am working on.

XJ900RK Carb Diagram.

 

How about rather than restricting the orifice on the filter side, opening the ports on the bottom of the slide. Don't many of the jet kits come with a drill for this purpose?... thoughts?

*edit*
just re-read the thread. nevermind. query addressed.

 

Just a question about what pods actually do. Do pods allow more air to get into the cylinder?

 

waldo, the stock air box gives a common mix of air to all 4 jugs & that is how these bikes with the CV carbs were designed to work, when you fit pods & re-jet, everything changes, you basicly have to re-engineer the induction cycle, I have just done this with a Kawa GTR 1000 with success.

 

As far as I see it, the pods allow more air to be available for each carb than the airbox does. Each carb can draw air from all around the outside of each pod. The stock airbox is very restricted....think about it--the only source for the air is the little tiny square insert at the back of the airbox. All the air for all four carbs enters into the airbox from there. THAT is quite a restriction right there.

Dave

 

I am just wondering what everyone thinks the pods do for an engine?

 

I don't know what everyone thinks they do for an engine. I don't have any pods on any of my bikes. I do have a set of brand new pods, though.....

Dave

 

We're taking a break from Pod discussions.

Pod discussions will resume after Summers over.

 

ok........


Summer's over

Dave

 

lol rick..... you started it!!!! a can of worms were opened because pods are the number 1 question on the fourm. i read all 5 pages of this thread and can tell you, im still lost! im officially stupid. I wanted to hardtail my maxim, which would force me to pod my carbs... but none of it made sense... you all talk to fancy. I understand the tubs... but when they have to be directed outside of the pod? i dont get how you could slide the pod over the carb and the tube?! i was originally searching to post to see if there were a way to (not for looks) construct a box around the 4 pods that would allow the proper air, but minimize the space under the seat to allow for a hardtail. rick..... my carbs are comming to you this winter to fix for pods i know you hate the p word, but your not that far away, and im not smart enough to figure all this out.... plus, i have a 4 into 1 from previous owner, so bike already blackens spark plugs and pops on down shifting.

 

anybody happen to know what size the hole in the bottom of the throttle slide is stock? I just buttoned mine up and forgot to check. I think the dynojet kit comes with a 5/32" drill to open it up. I was gonna sneak up on it in finer increments.

 

So if I build a PVC manifold with a single pod and use the stock boots, I should be fine...right or am I gonna have to read this novel again.

 

Seal the Atmosphere Vents.
Open the Vent behind the Horn opening.

The GREEN in this Photo illustrates one possibility.

Rubber Hose and Tee Fittings
-Or-
Remote Controlled Model Aircraft Tubes and Fittings.
Old School Chrome Plated Tubing.
(Tubing salvaged from telescoping antennas)