Topic: Pods off, airbox on = instant smoooooth!!

[Spanner 1]

My K1 750 has had pods since I got it and with a full service and vac. synch I think it was running PDQ, that is until today when I finally got a stock airbox and clean filter back on the bike. Definitely much smoother and no noticeable change in performance........yeah, it's still got 125 main jets ( stock is 120 ), but the open 4 into 4 may need that anyway...plug chop time again tomorrow.!

PODS: 0     AIRBOX: 1.

[Gordon]

The stock air box/air filter combo is a very misunderstood thing, and is often tossed aside without any consideration for its purpose and design. 

[schwebel]

I have put pods on several bikes and spent countless hours trying to get the jetting just right. But in the end the stock airbox just seems to work best.

[TwoTired]

I agree.

I have no trouble trading "style" points for a nice smooth running, predictable bike, easily tuned on the the first assembly.

I have a theory that people that wan't/use pods must also hit themselves in the head frequently.  Simply because it feels soo good when you stop.   

Getting used to the extra hassle of shifting a transmission, Spanner?

Cheers,

[Spanner 1]

Thanks for remembering my old 750A, TT !!..I would stop short of saying well now I've got a real CB750 !!, 'cos that Hondamatic despite 8to1 compression and 24mm carbs and all de-tuned would go forever and no stress 75mph all day long .....memories !!

[Hush]

Ha ha TT maybe TT stands for "too true"!

[Frankencake]

I know that pods are a pain to use but what about these one piece manifold/filters that I see around?  It seems logical that they have a better chance letting the bike run a bit smoother since the intakes are sharing airspace.  They seem like they would be easy to make as well.
Also, can someone tell me what velocity stacks are all about?

[HondaMan]

I know that pods are a pain to use but what about these one piece manifold/filters that I see around?  It seems logical that they have a better chance letting the bike run a bit smoother since the intakes are sharing airspace.  They seem like they would be easy to make as well.
Also, can someone tell me what velocity stacks are all about?

The velocity stacks direct the airflow to smooth it out and "aim" it directly at the carb's throat. Honda's airboxes all had velocity stacks inside the boxes, for this purpose. This makes the venturi action at the needle jet work just right.

There are pods out there that have velocity stacks inside. They are hard to find, it seems, but they will fit the "K" model 750s and work very well if even they do make the bike noisier. On the smaller Fours, the frame is in the way and these pods won't fit (too long, usually).

Rule of thumb for airbox + performance buffs: at any given instant, there is an airflow of (1.25 * carb throat size) passing through the airbox. So, if you make the inlet holes to that box (1.5 * carb throat size) minimum, you will not have any restrictions from the box. 

[tygrant]

threads like this make me feel so lucky with my 550, I bought it as a basket case when I put it all back together with bench synced carbs, I installed pods it had 110 mains in it. I fired it up and I havent had a single issue!, plugs look fine, no hesitating, idles smooth, not a single issue and I didnt even play with the screws. I really get the feeling this is far from norm.

[mkramer1121]

threads like this make me feel so lucky with my 550, I bought it as a basket case when I put it all back together with bench synced carbs, I installed pods it had 110 mains in it. I fired it up and I havent had a single issue!, plugs look fine, no hesitating, idles smooth, not a single issue and I didnt even play with the screws. I really get the feeling this is far from norm.

i thought the same thing until i put the airbox back on my 550 when i sold it, night and day difference....

[mystic_1]

Rule of thumb for airbox + performance buffs: at any given instant, there is an airflow of (1.25 * carb throat size) passing through the airbox. So, if you make the inlet holes to that box (1.5 * carb throat size) minimum, you will not have any restrictions from the box. 

So, for a CB750, carb throat diameter = 28mm, minimum airbox opening size = 1.25 x 28mm = 35mm...  Optimum = 1.5 x 28mm = 42mm.  I imagine anything larger than that is pointless?

I've noticed that honda varied the location and configuration of the airbox's intake(s) over the years, early airboxes had one large intake, later ones had two, one in front and one in back.  Was this to accommodate the jetting changes over the years? 

mystic_1

[HondaMan]

Rule of thumb for airbox + performance buffs: at any given instant, there is an airflow of (1.25 * carb throat size) passing through the airbox. So, if you make the inlet holes to that box (1.5 * carb throat size) minimum, you will not have any restrictions from the box. 

So, for a CB750, carb throat diameter = 28mm, minimum airbox opening size = 1.25 x 28mm = 35mm...  Optimum = 1.5 x 28mm = 42mm.  I imagine anything larger than that is pointless?

I've noticed that honda varied the location and configuration of the airbox's intake(s) over the years, early airboxes had one large intake, later ones had two, one in front and one in back.  Was this to accommodate the jetting changes over the years? 

mystic_1

The early one had a low window inside the vent and high output noise, so the next version had two windows (with middle-high thresholds inside) to reduce the noise. The third version came on the K2, where the window thresholds were raised too far: we opened them up for performance use. The last version had a long duct across the bottom of the box, opening backward to move the noise elsewhere. Those were real hard to get in & out, too!

[MRieck]

 Most people don't know how to really tune carburetors so I wouldn't "blame the game". They look at fuel circuits as individual operations and don't consider the overlap that exists. Example...The idle mixture circuit contributes fuel at WOT....it doesn't "shut itself off" past 1/4 throttle turn. Then there are the subtleties of needle diameter/taper, impact the main jet makes on the needle jet and needle, float bowl fuel height etc, etc. If your are going to individuals filters start with a quality piece which would be a K&N (not Emgo or Uni etc) and be prepared to have to (and know how to) address the changes to the fuel curve. Cam timing is a very similar subject....if you don't really understand what's happening.........
 
   

[GammaFlat]

We should all take note of what I would call the "fathers" of this forum.  The incredible depth of knowledge and talent by a handful makes all of our knowledge/abilities/bikes just so much better.  This is incredible.  I'll not name names (for fear of missing someone important  ) but they know who they are and a lot of us "lower beings" know who they are as well. 

THANKS and happy Father's  Day! 

John

[MRieck]

I agree.

I have no trouble trading "style" points for a nice smooth running, predictable bike, easily tuned on the the first assembly.

I have a theory that people that wan't/use pods must also hit themselves in the head frequently.  Simply because it feels soo good when you stop.  

Getting used to the extra hassle of shifting a transmission, Spanner?

Cheers,

 That appears to be a single sentence big guy. I've used that line for years to describe roadracing with fellas I've helped out. You can't teach a hammer to jump through a hoop either. A lot of guys I've known can break a crowbar in a sandbox. I can go on.........

[ofreen]

[That appears to a run on sentence big guy. I've used that line for years to describe roadracing with fellas I've helped out. You can't teach a hammer to jump through a hoop either. A lot of guys I've known can break a crowbar in a sandbox. I can go on.........

I used to tell the boss (before he got fired for being incompetent) that his problem was that the only tool he knew how to use was a hammer, so to him everything looked like a nail.

[cycleman]

Most bikes actually run better with the stock filter set up because it provides a dead air space & a trap for the air so the carbs can use it.  Pods on the other hand have nothing to trap the air going by. Racing bikes are a different animal as they live at the top of the rpm curve and are tuned for that range.

From what I know if you can increase the filter area ( bigger air box, dual filters, not really an option on a bike ) you will get an increase in performance.  Your increasing the volume of air available for the engine. Cold air intakes work as well.

Lots of debates on K&N verses stock paper element.  An old rule of thumb that I use is that if it flows more air it has to flow something else as well. The something else isn't good for engines.

[MRieck]

Most bikes actually run better with the stock filter set up because it provides a dead air space & a trap for the air so the carbs can use it.  Pods on the other hand have nothing to trap the air going by. Racing bikes are a different animal as they live at the top of the rpm curve and are tuned for that range.

From what I know if you can increase the filter area ( bigger air box, dual filters, not really an option on a bike ) you will get an increase in performance.  Your increasing the volume of air available for the engine. Cold air intakes work as well.

Lots of debates on K&N verses stock paper element.  An old rule of thumb that I use is that if it flows more air it has to flow something else as well. The something else isn't good for engines.

Paper filters do trap more particles...that is a fact. Volume is important and so is shape. Old frame designs do not allow for large airboxes so their efficiency is compromised.
 I have removed modern air box flapper systems (which improve low end torque) with no real noticeable drop in performance. The dyno has shown a very slight drop but you can't feel it and it improves top end power. Same thing with exhaust power valves. I have compensated with some light head milling to increase the CR which works out very well especially if stock cams (or mild performance cams) are being used.
 

[sangyo soichiro]

The more threads like this I read, the more I'm tempted to put my stock airbox back on.  I can't complain about how my bike runs currently; perhaps it could be a little better, but I plan to rebuild the engine and go to 836 this winter, so I'll fine tune it after the rebuild.

But these stock airbox arguments are really making sense to me.  TT already has convinced me to dump my inline fuel filters. 

[xenoscr]

I know this thread is almost a full year old but I just had to post and say I'm a true believer now. I finally got a stock airbox and all new boots, bolts, and filter. Put my jetting back where it should and fired up my bike and what a difference. It's never run so smooth. I had it running pretty damn good with the pods but it still sucked at low RPM. With the sock airbox I have a smoother idle at the lower RPMs than I was ever able to accomplish with the pods. I didn't notice any performance degradation either. The pods are going into a box on a shelf, they won't be back on my bike any time soon.

Ok, now this thread can slowly sink away for another year.....

XeNoSCR

[edbikerii]

Buncha wusses can't handle a little re-jetting....

You guys ask your mommies to open your beer bottles for you too?

 

[wannabridin]

The more threads like this I read, the more I'm tempted to put my stock airbox back on.  I can't complain about how my bike runs currently; perhaps it could be a little better, but I plan to rebuild the engine and go to 836 this winter, so I'll fine tune it after the rebuild.

But these stock airbox arguments are really making sense to me.  TT already has convinced me to dump my inline fuel filters. 

hey soichiro, you have any threads to show what TT's logic to this is??

[climbingaz]

I'm going to mount some of these on my bike....

[ev0lve]

TT already has convinced me to dump my inline fuel filters.  

hey soichiro, you have any threads to show what TT's logic to this is??

You don't remember this 6 page behemoth thread on filters? 
http://forums.sohc4.net/index.php?topic=48719.0

It is a gravity feed fuel system.  Gravity pulls down the fuel tubing not up the fuel tubing.  When the tube going up is the same length as the tube going down, gravity flow is negated.

I submit that one good filter is all you need.  The in-tank type is self clearing with the movement of the fuel in the tank.  
Further, if two filters were better or needed for added insurance, then isn't more insurance better?  If so, why stop at just two filters?  Why not five or six?  Just think how clean the fuel with be with ten filters in series with the tank feed?

Cheers,

[wannabridin]

i can't say i got around to reading that thread...  or if i did it was quite awhile ago and i don't remember the specifics.  i'll have to take a look at the arguments on there!  thanks iggy!!