750-4 just how does the stock airbox function?

I started out asking a different question here about what jets to use with what pods on a stock 750-4. However, I am reading a lot about how pods don't really work with CV type carbs, as the sliders are vacuum operated, not mechanically, and the stock airbox provides the right vacuum differential to make them work. This isn't really clear to me, and was wondering if someone can explain it better. Exactly how does the design of the stock airbox make this work? Is it the enclosed space of the box, with a centralized inlet, being common to all the carbs? Is the amount of space a factor?

If a somewhat smaller airbox of the same basic design (still common to all the carbs with a central inlet) was made, would the carbs work just as well?

Thanks!

A couple of years ago I chatted with Wiredgeorge about a airbox mod that's listed under articles on this site. The impression that I got was that our carbs (CV34's) work best with a steady, lower velocity stream of air.


I'm a wastewater engineer so I deal mainly with water hydraulics,and various biological processes the make some people squeemish, so air flow isn't my forte. However, I have taken those 34's apart numerous times and know where things are. The port that draws the air out of the vacuum chamber (thus raising the needle) is located on the intake of the carb before it enters the main carb chamber. When you twist the throttle, you increase the velocity through the carb, creating a lower pressure across the port which then draws more air out of the vacuum chamber, raising the needle.....) If you don't have a steady supply of air, I think you're going to get turbulance at the intake the the carb and that will affect your vacuum draw.

My thoughts on the matter. Can't really say how small you might make your airbox and still get it to work. You might what to ask Wiredgeorge.

I tried writing wiredgeorge at his website. He responded saying that he doesn't offer advice to people who are not his customers. Certainly understandable I guess, especially when his shop is busy, but no help. I'll research this elsewhere. But I think it would work, as long as the box envelopes all the carbs with a distinct opening.

This is a pretty complex subject, that for most of us is akin to maagic. The best modern airboxes are carefully designed resonance chambers that are tuned for a particular engine setup. Displacement, rpm, intake and exhaust velocities, cam profiles, et cetera, are variables that affect the final design. There has been quite a bit of discussion of ariboxes over at zrxoa.com. Several of the members there have conducted experiments that suggest that a well-designed airbox with a low restriction filter will yield more power than pods or a poorly designed box.
The air boxes on our old KZs were designed with cost, ease of manufacture and noise reduction as the primary considerations. I strongly suspect that a carefully modded factory box could easily feed even a stoutly modified engine without the turbulance and tuning challenges of pods.
The pods, however, open up extra space for storage, blowers, NO2 and such. They also make removal and installation of the carbs MUCH easier. Some of us also like that intake roar when we whack the throttle.
Your mileage may vary.

I bought the bike 7 years ago with pods on it. Never had a problem. CV34 carbs

polkat wrote:

I tried writing wiredgeorge at his website. He responded saying that he doesn't offer advice to people who are not his customers. Certainly understandable I guess, especially when his shop is busy, but no help. I'll research this elsewhere. But I think it would work, as long as the box envelopes all the carbs with a distinct opening.

wired george.....ahh...never mind....

From the Sportbike Performance Handbook by Kevin Cameron.
www.motorcycle.com/products/sportbike-pe...e-handbook-3929.html
www.themotorbookstore.com/sportbike.html

There is a way around the air box with a CV carbs. Stock the BS carbs are set up to work with the airbox, but they can be modified to work with the pods. Ive got my BS 34s workin real good with my K&N pods. Talk to Otaker, he may give more info.
Tom