Topic: So, you want to run pods?

[mark ward]

I'd almost be tempted to try the old airbox, if my Dyna module wasn't in the way; and if I could find it. I removed it around '76 or '77.
      Scottly, would you happen to have any of those allen screws, that fit your frame-connector kit?   (or a source to purchase same type)

[scottly]

Mark, I don't think your VM 29 Mikuni carbs will work with the stock airbox?
The small screws are #10-24 zinc plated. You may be able to find them at hardware stores like Ace if you only need one or two.

[cbrianroll]

I'd like to copy the design and dimensions of the stock airbox.( I do not want to spend top dollar on a used one and I have some metal I can bend up) does anyone know the dimensions and design of them?

[mark ward]

I believe you're correct Scottly. The VM29's air inlet is 44-45mm. ... I located the velocity stacks I bought back around '77; and I just ordered RamAir filter socks, which should slip over the stacks.
       I'll look around for the screws locally. A couple vibrated out, when I initially re-installed motor; and took bike out for a short test-ride. ....yup. My fault for not tightening them, assuming the short ride would cause no issue.

[JerrodR]

Hey guys, recently bought a project bike. Was able to get it running and going up the road, but am having major issues in the mid RPM range, sputter's and bogs. If I run through all the gears in higher RPM's, say between 4 and 6 thousand it actually runs pretty good. But say I'm cruising at around 3 in 4th gear, and accelerate, it will sputter pretty hard and eventually start to pull. It has a 4 into 1 with a hollowed out baffle. And the stock airbox, but the airbox was not on very well. Didn't seem to be seated in the far right carb at all when I took it off. Symptoms also seem to be similar to sticking floats, but does this sound like it could be a jetting issue? Any help or advice would be welcome, thanks guys..

[Jerry Rxman Griffin aka MuthaF'er]

Read your plugs

[JerrodR]

Yeah, everything I understand about engine's I've tought myself, I've never had a project I couldn't handle but in no way am I a machanic. Determining how an engine is running based on spark plug color isent a skill I've aquired, if that were the case I probably wouldn't be asking you guys for help. Anyways, it's got all new plugs now, and it's running alot better now then it was when I bought it so the old plugs probably aren't gonna be able to tell me much, But they were turning white the way it was running when I bought it. But it's doing much better after I replaced all the cables.

[mark ward]

It's running as if you just started it, after sitting all winter, without using STABIL or fuel stabilizer in the tank. (bad gasoline)    Or perhaps the intake manifold boots leaking.
 ....assuming ignition is o.k.....

[RAFster122s]

Running Shell gas will also lead to white deposits on the plugs according to HondaMan.

[HondaMan]

Running Shell gas will also lead to white deposits on the plugs according to HondaMan.

It can: that said, this seldom seems to foul the plugs, unlike the black carbon soot. It seems to be a deposit from a fuel additive they use (fuel injector cleaner? Dunno that part...). Locally the Sinclair gas runs similarly.

[tofan]

I have a question about the mechanics of running pods vs stock:

If all else equal and if I understand correctly, installing pods increases airflow causing the bike to run lean. This requires you to adjust the carbs to compensate.

Theoretically, could one restrict the airflow of the pods and not have to mess with jetting?

[HondaMan]

I have a question about the mechanics of running pods vs stock:

If all else equal and if I understand correctly, installing pods increases airflow causing the bike to run lean. This requires you to adjust the carbs to compensate.

No. Installing pods, as the 2nd message (from me) in this post explains, destroys the 3rd pressure zone that carbs need to be able to push fuel up the jets. I'd suggest going back and reading that until you understand this better. In some old cars, notably Cadillacs with their huge engines in the 1970s, the air filter was a restriction, but those have 1 carb feeding 8 cylinders in a constant-vacuum scenario: these are pulse-feed carbs, one per cylinder. This is an entirely different dynamic from a car engine with one manifold plenum feeding multiple cylinders. Virtually nothing is the same as in a car's engine.

Theoretically, could one restrict the airflow of the pods and not have to mess with jetting?

Theoretically, yes: in practice it is trial-and-error to get it to work, up to its limit. One way I have done it involved making covers for each pod filter (these were barrel-shaped, not cone-shaped, so it was possible to accomplish) that wrapped all the way around the pod and had a slot cut in each one that was 1/3 of the full-throttle cross-sectional area of the carb's 24mm throat (i.e., 16 square mm of opening). This worked OK until about 3/4 throttle, at which point the engine would not accelerate any more in the upper gears. The lower RPM ranges mixed properly and prevented the characteristic plug fouling, but the top speed was reduced to about 90 MPH. For that show bike, that was fine: for a touring ride it wouldn't be so good. And, we arrived at this size of opening by pure trial-and-error (and over 48 fouled sparkplugs and MANY weekends of testing) until the bike would run halfway decently in the important 1500-3500 RPM range so it wouldn't fall on its face every time the throttle was snapped open, or backfire from the constant overload of non-aerated fuel that pods cause in the normal riding RPM ranges. If you only run the engine at WOT, then yes, you can run pods with some success, although it was my (road)racing experience to see the winning bikes ALWAYS had the OEM airboxes on them - especially the 750.

The 500/550 will run OK with pods up to about 1/3 throttle, after which it suffers the same troubles as the 750, because they have very wide bells on their smaller-throated carbs. Trouble is, these bikes usually run right between 1/3 and 2/3 throttle most of the time, so they suffer from the issues, too. In the era of 55 MPH riding the 500/550 got away with pods mostly bbecause it wasn't running in the troubled RPM range, but today the old problems we saw in the 1970s are back because the speeds are higher again.

[TwoTired]

If all else equal and if I understand correctly, installing pods increases airflow causing the bike to run lean. This requires you to adjust the carbs to compensate.

This is false, as the only operating range the air volume could increase is at or near wide open throttle, due to slightly less restriction.  At all other throttle positions the stock arrangement provides air volume in excess of demand. I e, no limitation.  What pods do is shorten the air duct to present outside atmospheric air pressure (and turbulent air) right at the fuel jet exits.  It is the air pressure differential from outside atmospheric  that drives fuel though those jets.  The closer you get to pressure equalization across the jet orifice, the less fuel is delivered through a given jet orifice and leaner mixtures are the result.  You can attempt to restore mix ratios by enlarging jet orifices, but the turbulence in the carb throat changes position when velocities are varied, moving short, then over, then beyond the jet orifice exits, making fuel delivery different at various RPMs.
In essence, Pods may improve hp at wide open throttle by some small amount.  But, then you kiss goodbye street performance at many other throttle positions.  Then you either avoid certain RPMs or live with odd throttle behavior.  Honda designed a good street bike with their air filter system. 

Cheers!

[scottly]

This thread was doomed from the start to spread the misinformation regarding pods vs stock airboxes. Yes, pods can be successfully used with proper adjustments. The smaller bikes like 550s and 400s are more sensitive to changes than the 750s, which have a very large filter area. Mark and Lloyd, I believe you both are familiar with member Mooshie, who has racked up thousands and thousands of miles on her 550, EQUIPPED WITH K&N PODS!!!

[TwoTired]

Welcome to the new era where "misinformation" is information that you don't like as redefined by the left.  It's all the rage these days.

The early 550's are far more tolerant of induction issues.  Had a 75 CB550 I got with foam pods on it.  It ran ok around town with a Mac 4-to 1 on it.  Previous owner tried to "cafe" the bike, with myriad dumb mods.  Like having the clutch disengage with right turns due to tiny bars and poor routing.  And Koni shocks that wouldn't move up and down.  And no inner fender to keep water and road grime off the exposed PODS. Because, you know, that plastic inner fender is just SOOO heavy.  But, I digress.  Like my 74, the stock carbs run very rich.  They have to to pick up engine RPM under load from idle.  This was the saving grace for the POD MOD on this bike that allowed it to run ok.

I could have put thousands of miles on it the way it was, 'Cause it did run acceptably, just with stumble on throttle opening from idle, if you gave it too much too soon.  So, I checked for mods to the carbs on the 75.  As suspected, the carbs were in stock configuration.  Thankfully, the PO didn't screw them up.  Turning the pilot screws inward a half turn made the throttle work better.  But, it later started fouling plugs.  I think Mooshie had that issue, too, IIRC.  So, I restored the 75 with stock induction and set everything to factory settings.  Never had any more issues with throttle or spark plug fouling, and it still had the MAC exhaust on it when I later sold it.

See, I know how well the stock one behaves as I drove one for years.  Had I not known this, all the foibles that came with that 75 would have seemed "normal".  And I would have just adapted to the adverse behavior characteristics and driven it for miles and miles in ill tune without knowing how well it could run.

Could I have made the PODS work better than when I got them?  Yes, with a test track, and repeat plug chops and carb alterations (or paying the Dyno man).  But, in one day it ran like it should with no internal carb alterations, just by putting the stock air induction back on it.  And no more issues with riding in the rain or going though puddles made by errant irrigation.

Cheers,

[Scott S]

This thread was doomed from the start to spread the misinformation regarding pods vs stock airboxes. Yes, pods can be successfully used with proper adjustments.

 It was never meant to say you can't; only to point out that "Oh yeah, man! Just go up two on the mains!!" most likely isn't gonna cut it. It takes time, tuning, perseverance and knowledge. Plug chops and/or dyno time. I'd be willing to bet that 95% of the people that slap on pods never take the time to dial them in correctly.
 

The early 550's are far more tolerant of induction issues.  Had a 75 CB550 I got with foam pods on it.  It ran ok around town with a Mac 4-to 1 on it.  Previous owner tried to "cafe" the bike, with myriad dumb mods.   Like my 74, the stock carbs run very rich.  They have to to pick up engine RPM under load from idle.  This was the saving grace for the POD MOD on this bike that allowed it to run ok.

I could have put thousands of miles on it the way it was, 'Cause it did run acceptably, just with stumble on throttle opening from idle, if you gave it too much too soon.  So, I checked for mods to the carbs on the 75.  As suspected, the carbs were in stock configuration.  Thankfully, the PO didn't screw them up.  Turning the pilot screws inward a half turn made the throttle work better.  But, it later started fouling plugs.  I think Mooshie had that issue, too, IIRC.  So, I restored the 75 with stock induction and set everything to factory settings.  Never had any more issues with throttle or spark plug fouling, and it still had the MAC exhaust on it when I later sold it.

See, I know how well the stock one behaves as I drove one for years.  Had I not known this, all the foibles that came with that 75 would have seemed "normal".  And I would have just adapted to the adverse behavior characteristics and driven it for miles and miles in ill tune without knowing how well it could run.

Could I have made the PODS work better than when I got them?  Yes, with a test track, and repeat plug chops and carb alterations (or paying the Dyno man).  But, in one day it ran like it should with no internal carb alterations, just by putting the stock air induction back on it.  And no more issues with riding in the rain or going though puddles made by errant irrigation.

Cheers,

 My point exactly. How many people on this thread have said "I was able to make the pods work OK, but it ran so much better with the stock air box"?

[PeWe]

It would be fine to gather success stories about use of pods which I was convinced this thread should collect.
-Bike model?
-Stock or how modified?
-Exhaust system?

Even a stock bike will need different jets if using an exhaust with better flow, usually louder and stock air filter.

As I wrote before, my CB750 with 836 and more ran fine with stock carbs and pods back in the 80's.

Same bike has other carbs now and still pods. No pods related found, only the correct jets for smooth correct AFR and max power that can be tricky and time consuming to find out.

Had the smoothest fine running bike a few days ago from a perfect idle and all the way up,  but not the amount of torque I have felt before when twisting. So back to the drawing board

[TwoTired]

It would be fine to gather success stories about use of pods which I was convinced this thread should collect.

As I wrote before, my CB750 with 836 and more ran fine with stock carbs and pods back in the 80's.

Same bike has other carbs now and still pods. No pods related found, only the correct jets for smooth correct AFR and max power that can be tricky and time consuming to find out.

The problem with "success stories" is that they are quite seldom quantifiable, or delineated with consistent part number references, or have any performance numbers to compare with what the stock bike performance numbers are.  For some, a pod from K&N is the same as a pod from uni, is the same as a pod from china.  Can you really believe all these pods will replicate the same performance numbers?  Can you even believe all these pods from within the same manufacturer will perform the same, sample to sample?  How much have they invested in quality control to make a consistent product for the very cheapest price offering?  Same thing can be said regarding exhaust systems.  There is no flow data available to say if a manufacturer's exhaust from 10 or 20 years ago is the same or made in the same way as what is available today.

A bike build from parts with a trip around the block, while certainly a success story, really has no data to support that it works better than stock in any or all aspects.

Loud exhaust and intake can SOUND bad ass. Sometimes giving the illusion of better performance.  But, how does it do next to a stocker?  Are the drag E.T.s better.  Does it pull out of corners as crisply?  Do you need to keep blipping the throttle during long idle to keep the plugs clear?  Are the average engine temps now higher with pods and too lean a mixture?  (longevity impact).  Was the perceived improvement due to weight reduction or gearing change rather than a HP increase?

I'm not saying you didn't improve your bike PeWe.  All I'm saying is that not everyone's perception matches actual reality.  How does one know there is an improvement without actual and repeatable test numbers?  Without that, "running fine" can mean a wide range of performance numbers.  Further, it matters whether the goal is a well performing all weather reliable machine.  Or, one that simply makes it first to the end of quarter mile one weekend before rebuilding or modding.

Finally, one of the first things you learn about production engineering is that a test case of one proves nothing, as far as repeatability.  All the "success stories" gathered here will be from one-off test cases, with no guarantee any singular recipe can be repeated successfully.  That's both the blessing and the curse of unique machines we customize for ourselves.

Cheers,

[PeWe]

The meaning of this thread was to find out...

Pods for me is KN pods design. The foam pods have been mentioned in other threads to have a problem in its design.

Original airbox not an option on modified engines that need more air.

Chopper guys another group where the estethics is very important. The slim design of that kind of bike is different than a stock bike where the stock airbox is not that visible as on a chopper.

My CB750K2 with stock airbox but better flowing HM300 style exhaust needed diferent setup than a HM341 system a friend use on his bike
Same jets as my K6 had from the very beginning with 341 pipes.

So the exhaust makes difference independent of which filter used.

Lots of tuning parts need help when assembled to run as it can.

[bigutah]

So, what’s the advice on CR29’s with K&N pods, Same as Hondamans explanation?


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[seanbarney41]

see that's the thing...roundtop keihin cb750 carbs? just an ok selection of main jets and pilot jets.  No alternative for changeing jet needle, needle jet, or air bleeds.  Stock keihins on the smaller sohc4 offer even less alternatives.  CR29 offers a much wider array of tuning options...better yet, get some Mikuni's, basically infinite spectrum of tuneability...

[HondaMan]

This thread was doomed from the start to spread the misinformation regarding pods vs stock airboxes. Yes, pods can be successfully used with proper adjustments. The smaller bikes like 550s and 400s are more sensitive to changes than the 750s, which have a very large filter area. Mark and Lloyd, I believe you both are familiar with member Mooshie, who has racked up thousands and thousands of miles on her 550, EQUIPPED WITH K&N PODS!!!

She does indeed have those pods, and they are blocked off about 50% of their surface to reduce the turbulence that was affecting her midrange (3500-5000 RPM) performance. I worked with her after rebuilding her engine and got the info to her mechanic that was reassembling everything for her. The new engine was acting differently from before and fouling plugs, so I had him block off about 50%-70% of the surface of the pods to pull air form a common space, facing each other, in the 1-2 and 3-4 carbs sets. I also had him extend the bowl vent tubes all the way up under the seat. The bike has a large fairing aboard (Vetter, I think?) and I understand (but have not seen) that the lowers are available: if so, that would help even more to quiet the air for the mix, much like my own bike. In the end she wrote back to comment that she had a lot more power when running onramps to the freeways where she often rides, and the plugs were behaving OK with the proper heatrange: the mechanic had started with the D8E plugs, which are too cold for this engine.

All else being similar: the early 627 carbs found in the CB550K1/2 engines (and some of the K3) have very large bell zones with small throats, nearly 70% larger (when comparing carb throat size to carb bell size) than in the 750's roundtops or PD type carbs. This combination acts to pull emulsifier air from a zone further outside the main feed (moving air) zone than those in the 750's carbs, which helps to raise that air pressure a bit and smooth out the transition between the idle and main circuits (which the 750 struggles with). To feed this air, the plenum had to be very quiet, so Honda went to great length (and expense!) to create the exotic air system in the CB500/550/350F/400F bikes, like none seen before. Honda never spent a yen on anything they didn't think they absolutely needed to, so the inclusion of such an air intake tract speaks loudly as to how important Honda/Keihin thought it was!

[RAFster122s]

Mooshie’s fairing is an Emgo Viper, older design mini fairing…

[MRieck]

I translated this from a swedish site www.braigasen.se
The owner is a real carb-guy

Carburetor with fuel screw
Most common on 4-stroke carburetors (except Mikuni HSR). A fuel screw is always located downstream of the throttle and is pointed

Umm...Keihin doesn't make a single carb that I have ever seen in which this is the case. All Kehins use an AIR screw for the idle circuits. A few Harley carbs (notably the old Linkerts) use an adjustable main jet that DOES adjust the fuel orifice, maybe this is what he is referring to? Or, maybe some of the Mikunis he is speaking to have adjustable mainjets, but I have not seen one like that.

Automotive carbs like Holleys, FoMoCo, and Carter, use fuel metering screws for the idle circuits (which is opposite the Keihin method), which confuses some folks who don't know about the differences.

Keihin FCR carbs use both an idle circuit air screw and a fuel screw.

[Translations]

Just to add fire to the flames i'd like to add that my bike runs great with pod filters. Has power all the up to 11,000 + rpm's. Doesnt run perfect but runs damn good once its warmed up...

78' CB750F3
- Rebuilt .50 over OEM Pistons
- CX-1 Webcam
- Dyna S ignition
- CBR600 coils
- Stock carbs w/ K&N pods