Topic: Pods Thread

[tygrant]

i never had my sled on a dyno anything llike that, but the first year i ran the machine stock and a freind had a snowmobile that was just a tad faster on the lake, we raced so many time i cant count. i was consistenly 3 -4 lengths behind him.the next winter after i got it dialed in i was consistantly just ahead of him. im convinced it was the ufo set up. as they were the only differnces. not only that i ran the machine in several radar runs both years and saw a 3-4 mph gain in the 1000 foot radar. no other mods were made to the sled and traction was comparable on glare ice with the same stud set up(probably less grip the second year due to wear on the studs)

i see where your coming from about the engineers at mikuni knowing what they are doing, but there is allways room for improvements over stock. my guess for not incorporating them into the original design would be how finicky the engine was after they were installed, i allways was rejetting that thing, (especaily after the carbon fiber rotor valve and pipe) more hp mean more problems  most of the time.

i too know that the cost to manu that part is next to nothing, but im sure they spent their fair share on R&D as well, where the reall cost is.   i think they would something cool to try out on a race bike but not for a Daily Driver, the gains wouldnt be worth the hassle

[MRieck]

 No one has mentioned the fact that charge is going in both directions especially at the RPM levels achieved by even these old bikes. And I mean a lot and long intake tracts make the fact worse. Slide shapes etc are not just dictated by positive charge.

[edbikerii]

Mike, do you mean that the intake valve is open during overlap in the compression stroke?

No one has mentioned the fact that charge is going in both directions especially at the RPM levels achieved by even these old bikes. And I mean a lot and long intake tracts make the fact worse. Slide shapes etc are not just dictated by positive charge.

[paulages]

Mike, do you mean that the intake valve is open during overlap in the compression stroke?

No one has mentioned the fact that charge is going in both directions especially at the RPM levels achieved by even these old bikes. And I mean a lot and long intake tracts make the fact worse. Slide shapes etc are not just dictated by positive charge.

that is what he means. the intake valve doesn't close until part way up the intake stroke of the piston. imagine the air rushing in during the intake stroke, perhaps assisted by the pull of the exhaust stroke (there is valve overlap there as well), and then the piston suddenly changes direction. it might seem like you would want the intake valve to close at exactly this moment, but in reality the velocity of the incoming air is able overcome the compression forces to a certain degree allowing a little more charge into the cylinder. however, the aforementioned forces varying with RPM and load, etc. throw in valve float at high RPM, and you get reversion- or air traveling back up the intake tract until the intake valve closes. intake design, cam profile, cam timing, cylinder profile (oversquare, undersquare, etc.), and several other factors all affect this situation. i'm sure the engineers on here could explain this fluid motion better than i.

[valvolux]

hey, new to posting here, be kind!

Read the Pods vs Airbox thread, plus the links to other threads discussing the pro's and cons to putting on pods.
All great information which will come in handy, but it all relates to the stock CB550K carb.

Despite doing a thread search, I couldn't find any info regarding experience with CRS roundside carbs, like advertised by old bike barn:

http://www.oldbikebarn.com/Motorcycle_Parts/Carb-Assembly



Could anyone provide some insight on what to expect if one ditched the stock 22mm Keihins carb and put on a Keihin 26mm CR Roundslide carbs with emgo pods?

Even the ad has the "proceed with caution"....
Is that because a extensive knowledge of carb tuning is required, or because despite the claimed +10% output its not really designed for road use, like increased fuel consumption, more erratic power delivery etc

Any thoughts? 

[mark]

Even the ad has the "proceed with caution"....
Is that because ...

it may be the reputation of old bike barn....

see ' Feedback - Bad Folks '

 

[edbikerii]

Interesting, yes.  Any idea how that is affected by pods vs. the stock airbox?  I'd like to think that reducing restriction would increase the speed of the intake charge sufficiently to overcome the compression somewhat, but my intuition tells me that lower intake restriction might permit the compression stroke to push more charge into the intake runners during that valve overlap.

Any experiences/theories?

Sorry valvolux, I don't have any experience with CRS roundside carbs.  I've only used stock carbs, as I think they are more than sufficient for my bone-stock CB550K engine.  Are you going to be racing the thing, or are you just looking for an alternative to cleaning up your old carbs?

Mike, do you mean that the intake valve is open during overlap in the compression stroke?

No one has mentioned the fact that charge is going in both directions especially at the RPM levels achieved by even these old bikes. And I mean a lot and long intake tracts make the fact worse. Slide shapes etc are not just dictated by positive charge.

that is what he means. the intake valve doesn't close until part way up the intake stroke of the piston. imagine the air rushing in during the intake stroke, perhaps assisted by the pull of the exhaust stroke (there is valve overlap there as well), and then the piston suddenly changes direction. it might seem like you would want the intake valve to close at exactly this moment, but in reality the velocity of the incoming air is able overcome the compression forces to a certain degree allowing a little more charge into the cylinder. however, the aforementioned forces varying with RPM and load, etc. throw in valve float at high RPM, and you get reversion- or air traveling back up the intake tract until the intake valve closes. intake design, cam profile, cam timing, cylinder profile (oversquare, undersquare, etc.), and several other factors all affect this situation. i'm sure the engineers on here could explain this fluid motion better than i.

[paulages]

Interesting, yes.  Any idea how that is affected by pods vs. the stock airbox?  I'd like to think that reducing restriction would increase the speed of the intake charge sufficiently to overcome the compression somewhat, but my intuition tells me that lower intake restriction might permit the compression stroke to push more charge into the intake runners during that valve overlap.

Any experiences/theories?

Sorry valvolux, I don't have any experience with CRS roundside carbs.  I've only used stock carbs, as I think they are more than sufficient for my bone-stock CB550K engine.  Are you going to be racing the thing, or are you just looking for an alternative to cleaning up your old carbs?

Mike, do you mean that the intake valve is open during overlap in the compression stroke?

No one has mentioned the fact that charge is going in both directions especially at the RPM levels achieved by even these old bikes. And I mean a lot and long intake tracts make the fact worse. Slide shapes etc are not just dictated by positive charge.

that is what he means. the intake valve doesn't close until part way up the intake stroke of the piston. imagine the air rushing in during the intake stroke, perhaps assisted by the pull of the exhaust stroke (there is valve overlap there as well), and then the piston suddenly changes direction. it might seem like you would want the intake valve to close at exactly this moment, but in reality the velocity of the incoming air is able overcome the compression forces to a certain degree allowing a little more charge into the cylinder. however, the aforementioned forces varying with RPM and load, etc. throw in valve float at high RPM, and you get reversion- or air traveling back up the intake tract until the intake valve closes. intake design, cam profile, cam timing, cylinder profile (oversquare, undersquare, etc.), and several other factors all affect this situation. i'm sure the engineers on here could explain this fluid motion better than i.

this is where TT or hondaman's engineering pedigrees would help... as i understand it, "reducing restriction" is not exactly the right way of looking at it here, as it's more about the difference in pressure in the chamber vs. that at the carb throat where the fuel is metered, as well as port design and air velocity.

i could be wrong here, but as i understand it, that this is why some modern four-valve intake ports are actually smaller than the carb throat: the reduction in port size (creating a venturi effect, much like velocity stacks) increases the velocity, and creates more of a bottleneck for reversion. big isn't always better, but in the case of these particular bikes, the port improvements have been pretty well proved in that regard.

someone who knows what they're talking about more can step in now...

[TwoTired]

One of the reasons why you can even USE a mechanical slide carb is that the vacuum pressure from the cylinder pulses.  This allows the sideways forces in the carb throat to stop or be relieved enough for the slides to move up and down freely.

It also means that the air flow through the carb is not constant at any speed.  The intake stroke gets the air moving toward the cylinder.  When the valve closes, the air flow stops at the back of the valve.  With high speed dynamics, the sudden closure causes a reflected shock wave back toward the carburetor.  Pretty hard to keep airflow laminar with reflected waves, and pulsing vacuum draw.

Cheers,

[w1sa]

Hello All,
This topic is of particular interest to me. The questions I'm about to ask do not relate to SOHC Hondas, but the subject matter and contributions seem too informative to pass-over for another thread.

My application is a 1970 twin cylynder/twin carby kawasaki 650. Mikuni round slide VM28 carbs.
The standard carb air filters are Vokes style rather than air box i.e. the air path to the paper filter is not 'restricted' seriously by a small air inlet to a closed  air box, but vented in an open fashion thru multiple inlet paths thru the cannister/can exterior of the filter unit.

The original parts are unavailable. I can rebuild the original (damaged) cans but I cannot find a replacement paper filter that would suit.

If I go the path of say K&N 'pod' filters, would I be faced with the same serious level of upset to the air flow etc. as that of changing from an air box set-up.

My initial thought is that the main consideration is the material difference/flow capacity of the different filter elements and the relative surface area of the filter selected.
Assuming the same surface area, would a high flow element necessarily change the fuel air characteristics.?
 
If so would an element of less surface area better 'balance' the carburetor and possibly limit the needle/jet changes for correct mixture (these parts are hard to come by as well)?Mains needle is adjustable (5 positions) to/across specified jets 200,210,220,230 &240. Mine is a 220. Raise the needle?

Hope you can help.

[Maxacceleration]

Ok, how about running the airbox with the top removed. How would this change characteristics?
Would low rpm flow be adaquate with a Uni stock replacement filter, but still enjoy the benefit of much more air drawn in at higher rpms?

I know someone who runs their stock airbox with NO filter or airbox lid. He claims more power...

Really, its takes a good tuner, with dyno time to verify anything.
And of course $$$... 

Seat of the pants is so misleading.

[paulages]

Ok, how about running the airbox with the top removed. How would this change characteristics?
Would low rpm flow be adaquate with a Uni stock replacement filter, but still enjoy the benefit of much more air drawn in at higher rpms?

I know someone who runs their stock airbox with NO filter or airbox lid. He claims more power...

Really, its takes a good tuner, with dyno time to verify anything.
And of course $$$... 

Seat of the pants is so misleading.

i ran my cb550 with a uni filter and the top removed for a couple years until i got the 718cc engine in. it ran very well like that, with stock jetting.

[goon 1492]

Thank you TwoTired, your level of knowledge amazes me, always. For the anyone else if you can't understand his explanations......read them again, it will come to you.

[valvolux]

Sorry valvolux, I don't have any experience with CRS roundside carbs.  I've only used stock carbs, as I think they are more than sufficient for my bone-stock CB550K engine.  Are you going to be racing the thing, or are you just looking for an alternative to cleaning up your old carbs?

Cheers for replying ed, I guessed as much re: the CRS carbs.
Shame, it would be good if someone had some anecdotes regarding the ease of turning them. They claim its an easy process, "with pre-jetted installation, bolt on and ride...." but from reading this thread, I doubt that.
I can get 26mm CRS carbs here in australia no problems, so I wouldn't be getting therm from old bike barn. I was just curious regarding the caution comment they list.

I have the same model as you and i'm in the process of turning it into a cafe, so your summary regarding the tuning of your carbs with pods will im sure prove invaluable if I keep my OEM Keihins. Many thanks. By the way, what size pods did you get? OBB suggest 39mm (1 1/2") pods for a CB550, but CRC2 says 35mm (1 3/8"). I have four of the former.

I really am committed to getting pods to work because the battery and electrics are getting relocated to the tail and aesthetically the whole bike will not be up to par if I retain the airbox.

The stock carbs have done 57,000 kilometres and are 30 years old, so I was thinking of just starting from scratch.
No, the only racing i'll be doing is around my neighbourhood and maybe the occasional track day. Its not going to be a commutter.

Yes, like everyone, I am looking to get a few more horses out of the CB. Its supposed to be a cafe racer, not a cafe commuter 
Thus the upgrade to a CRS carb is a option im considering. A new 4-2 peashooter exhaust is replacing the cheap aftermarket 4-1 pipes currently on the bike.

[edbikerii]

Have another look at the link in my sig, it points out which pods I used and where I bought 'em.  Others swear by K&N.  After about 5,000 miles, I'm still happy with my Emgos.  Whatever floats your boat!

Sorry valvolux, I don't have any experience with CRS roundside carbs.  I've only used stock carbs, as I think they are more than sufficient for my bone-stock CB550K engine.  Are you going to be racing the thing, or are you just looking for an alternative to cleaning up your old carbs?

Cheers for replying ed, I guessed as much re: the CRS carbs.
Shame, it would be good if someone had some anecdotes regarding the ease of turning them. They claim its an easy process, "with pre-jetted installation, bolt on and ride...." but from reading this thread, I doubt that.
I can get 26mm CRS carbs here in australia no problems, so I wouldn't be getting therm from old bike barn. I was just curious regarding the caution comment they list.

I have the same model as you and i'm in the process of turning it into a cafe, so your summary regarding the tuning of your carbs with pods will im sure prove invaluable if I keep my OEM Keihins. Many thanks. By the way, what size pods did you get? OBB suggest 39mm (1 1/2") pods for a CB550, but CRC2 says 35mm (1 3/8"). I have four of the former.

I really am committed to getting pods to work because the battery and electrics are getting relocated to the tail and aesthetically the whole bike will not be up to par if I retain the airbox.

The stock carbs have done 57,000 kilometres and are 30 years old, so I was thinking of just starting from scratch.
No, the only racing i'll be doing is around my neighbourhood and maybe the occasional track day. Its not going to be a commutter.

Yes, like everyone, I am looking to get a few more horses out of the CB. Its supposed to be a cafe racer, not a cafe commuter 
Thus the upgrade to a CRS carb is a option im considering. A new 4-2 peashooter exhaust is replacing the cheap aftermarket 4-1 pipes currently on the bike.

[valvolux]

glad to hear they are working well for ya. They look better than K&N anyway.
Apologies, I thought I had read the thread quite closely. Reading betwen the lines, I gather you got them from CRC2 so you have the (1 3/8").
That means I have the wrong size.
They would probably fit the 26mm CRS carbs. Perhaps thats an omen for which way I should go.

[Kalamazoo]

So, Im going to be running Pods and straight pipe on my 1976 CB 550, wondering if any advice on jets to use, I was thinking something like 120 mains?

[wireman]

I have a 750 run pods and straight pipes and am running a 122.5 jets

[karmasic]

4/1 4/2 4/4?


i think 115 should be a good place to start on a 550. 120 might be a hair on the rich side.

[Kalamazoo]

Alright, I'll start at 115 and if not enough make my way up, jets are cheap anywho.

[cafe750]

I'd recommend brass jets, with small holes in 'em.
Besides jet sizes, you'll want to play with needle position...there is no quick and dirty formula to carb jetting....

[buffalogt750]

I have a 1976 cb550K with stock 4 into 4 pipes and pods and run 115 mains and needles in stock position. I'm happy with this setup. Pipe mods don't seem to affect jetting as much as air filter changes.

[karmasic]

just remember that rich is better then lean, if you have to choose.

[Sporkfly]

just remember that rich is better then lean, if you have to choose.

Even that can be argued. Rich will wash oil off of the cylinder walls and you'll wear pistons, rings and cylinders out pretty quick. Both rich and lean conditions can ruin valves.

If you have to choose, jet it right or put it back to stock!

[Kalamazoo]

Thanks for the info, Oh and sorry I didnt say what kind of pipes im running... running 4 into 2