A Pod Filter Thread for Geeto.....

That's because the orifice circled in the picture, below is what creates the vacuum to lift the slides in a CV carb. Blocking that orifice will slow down the vacuum and venting to lift and lower the slide. (you probably know that, but I am just clarifying why.)

*this photo is from GSresources.net

I had the emgo pods on my CX, ran OK (sort of) but not well at all. Finally noticed this issue and switched over to MikeXS pods a few months ago, they also have the internal velocity stack and dont block the ports (on the CX carbs the emgo pods blocked the ports completley). It's a different bike after the cheap ass pods got chucked in the bin.

This pic shows how badly they block the ports on the CX carbs



Cheers
Steve

this seems as good a place as any to talk about the airbox plenum and it's effect on how a motorcycle operates (and please forgive me if I get some of the scientific terms wrong I am a backyard guy). If you ever look at the airbox on say a cb750 - you will notice that it has a filter and a chamber. That upper chamber is the air plenum. What is an plenum you ask? it is basically a room where the intake air is 'normalized' to be consistent in pressure. That means when the carbs draw in air they are all drawing in air that is pretty much the same density, humidity, and temperature at the same rate. hwat effect does this have? well if all the carbs are basically seeing the same air then there is going to be less variation in the air/fuel mixture and the cylinders are all going to make roughly the same power - meaning the bike will run smoother and have more consistent power. This affects driveability more than it does outright power but on a street bike driveability is what most of these cafe kids complain about when they say their bike "isn't running right" - the sputtering, the surging, etc... When you expose the open mouths of the carbs to the outside world you can't always gaurantee each carb is getting the same airflow, as your speed increases your airflow changes (the box notices no such change).

how effective/prevalent is this technology? well in the 1960's virtually nothing motorcycle (except maybe a few desert sleds) had a still air plenum outside of the intake tract, but now every single new vehicle has it. on most sport bikes it is the area the ram air feeds under the tank before the air filter. even modern moto GP bikes have an air chamber under the fuel tank - just no filter. Racers are always tuning for atmospheric conditions anyway, be it fuel maps or the old jet and needle dance, street bikes aren't, so having a more senstive setup puts you at a disadvantage if you aren't adjusting your fuel mixture all the time.

Thought I'd put this here, the people who matter will understand it and it's something to look at for the rest
My 1974 CB360 with 378cc modification Ignore numbers along bottom run was ~2,800 to 9,500rpm.

posted from another thread at Marc's request:

Pods aren't the work of the devil, they aren't nearly frustrating enough. However, there is a lot of misinformation and just general stupid logic that goes through a newbie's head when it comes to this area that the job is actually a lot harder than it is. Most newbies don't have the patience for it either or the methodical approach to develop the necessary skills to properly dial in carbs. I probably shouldn't have to say this but all carb tuning and evaluation should be done at operating temp. You would not believe how many people I know that complain about rough running on an aircooled engine while it is still on the choke and warming up.

common misconceptions:
- They are a performance upgrade: This is just flat wrong and it is derived from the worst place of all....working on cars. Back in the 1950's-1970's carb'ed cars usually ran restrictive air filters assemblies. Why? it as cheap to do so, it was easy to tune for regular partial throttle use, it helped make torque....who knows. All I know is that you took the air cleaner off your 440 siz pack superbee and the car made slightly more horsepower. So people think this applies to all mechanical things. However, most performance motorcycles starting in the mid 1960's were the result of Grand Prix racing technology (esp the japanese) and you saw things there that hadn't trickled down to stock performance cars yet - OHCs, multiple carbs, velocity stacks, etc. In most cases, esp amoung the japanese bikes, the engineers put a lot of thought and design into the intake tract to maximize performance, reliability, and part throttle fueling. Often if you delete this engineering one of those things suffers (usually partial throttle fueling). I have never seen a stock multiple carb setup benefit from individual filters, often I see them lose power. Why do you see them in high performance applications? well, in racing smooth partial throttle is less of an issue, plus once you upgrade the carbs the airbox rarely fits and if you went with a larger carb size and changed the flow characteristics of the head, then the plenum size of the airbox may not be properly sized for the airflow needed and you end up with a restriction.

- All filters are created equal: This is just bunk. When it comes to filters in motorcycles, you get what you pay for. If you buy cheap EMGO pods (often rebranded as other mfg or reseller's parts like Dime City Cycles or Dixie) you usually get a filter material that doesn't filter, is more restrictive (if the paper is intact) and the inlet will have a blockage in it that may obstruct vacumm passages that otherwise are needed to remain open. But they are usually $10 and price is more attractive when you have no fucking clue what you are doing. Filters from name brands like K&N and UNI are generally better, and for a "universial" filter they are going to be as good as it is going to get but they are oftern $20-$50 a filter and often require more maintenance than a stock filter (perodic oiling) and suffer shorter lives (esp if you ride in the rain). At the end of the day you are still getting a lowest common denominatior velocity stack shape vs the designed specifically for your application velocity stack shape of the stock airbox connecting rubbers.

- If you have pods and an exhaust you have to rejet one size up: This is just stupid logic perpertrated by idiots looking for an easy answer who don't understand carb tuning. Will you have to rejet? you might. It is a guarantee that you will have to do it....no. Carb jetting depends on a lot of factors like density altitude, actual altitude, barometric pressure, tempreature, humidity, etc. Getting jetting advice on the internet, specifically jet size numbers, is like asking getting masturbation advice from a eunic. In order to properly tune a carb you must first need to know how the carb works through out all it's throttle positions. Plus you must know how to evaluate an engine and it's fueling conditions. Than means plug reads, test rides, lots of time. When you open the throttle in your hand you have to have in your head what is actually going on in the carb as the slide lifts - if you can't picture that, you have no business poking your pecker at carb internals. Getting optimal fueling isn't a one shot process - if yu aren't tuining with a dyno and an o2 sensor then there is a lot of trial and error in getting the fueling spot on. And there are instances where certain carb just won't be receptive to the filter's airflow characteristics. Case in point - I have a GTO with a 400 ci pontiac mill running a 1969 GTO HO Quadrajet. At one point I ran one of those K&N filter tops where it was able to suck air directly from the top of the filter. Every time I stepped on the gas to open the secondaries the carb would backfire. I put a normal air filter top back in place the car ran fine. I used that filter top on any non Quadrajet carb car it ran fine. Every single quadrajet equipped GM car I put it on (a friend's chevelle, A camaro, a 350 chevy powered firebird, my GTO, A friends 442) had a carb backfire when the secondaries open. That carb design just didn't like that filter design. Sometimes it happens - often with parts that weren't specifically designed to work with each other but rather generally work of a large variety of applications - like pod filters.

- I'm never going to learn unless I do it: Bullshit. This is the mantra of the uninitated right before they get in over their heads. While I do agree experience is the best teacher, Carb tuning is a science and like any science it takes more than a set of screw drivers and a positive attitude to get good results. Mostly it takes reseach and a measured scientific approach. Again know your carb and know how it works in both theory and practice. Know the signs of how an engine responds to different fueling conditions and how to recognize them. Change only one thing at a time and evaulate the response. Test, Test, Test and collect data as you do it. Pay attention to variables like weather conditions. Use proper tools - can't tell when an engine is running slightly lean? use an o2 sensor or a dyno. Use your head. Are there guys who can pop open a set of carbs, do a bunch of changes, and have it be almost spot on? yes those people do exist and they got there through thousands of hours of trial and error and being methodical and through.

- "There is no point in being in this hobby unless I can't get exactly what I want and what I want is the look of pod filters because they are sooooo cool": Do I even need to point out how dumb this is? Sadly this is the attitude of most (but not all) new riders or newbies to old motorcycles. I call this the spoiled hipster newbie attitude. Honestly, motorcycling is a rich and rewarding hobby and if all the satisfaction you are getting out of it is in the value of how cool your bike looks to you then clearly you aren't getting the full measure of enjoyment from the hobby. But don't despair - motorcycling may just not be for you. There are plenty of other pursuits out there. Plus you can always pay an expert to just work on your stuff for you. There are other options.

* I am going to add one thing here at the bottom. Pod filters tend to be a typical newbie trap. It sounds like a job that is easy enough, after all it is just changing a filter, and has a high yeild of job satisfaction based solely on looks. However, most noobs who buy old motorcycles and don't have a clue what they are doing have usually already bought a collection of little projects that the application if individual filters plus a lack of tuning knowledge would already exacerbate. It is for this reason that I highly recommend that if you are considering doing this job you make sure that all these other tasks are done first:
- points oiled and serviced (gap and dwell set)
- Timing set and advance mechanisim checked and oiled
- new plugs
- new wires
- Coils tested and showing excellent spark (or replaced)
- Carbs rebuilt and cleaned with all new rubber parts
- Carbs set to factory tuning specs and properly synched with stock airbox in place
- All fuses in good working order
- No shorts in electrical system
- Charging system in good condition and charging according to factory specs
- Battery new or tested good.
- Exhaust gaskets replaced and heat cycled.
- Intake manifold rubbers replaced.
- Compression tested (hot) and shown to be with in spec.

Once all these tasks are done then you will have eliminated 99% of the issues that can mask themselves as carb tuning problems or be made worse by a filter change. At this point you should have an excellent running machine and a perfect baseline to get optimal fueling. Kind of a long list isn't it? How many newbies do you think just assumed that since the bike was running ok (without knowing what an ok running bike was really like) they could tune carbs? If you answered all of them you are probably right.

Another note on removing air boxes and installing pods.
Personally I don’t have a problem with pods depending on what carburetors they are being installed on and if they are of decent quality/fit. I have a pair on my GL500. In this case, the stock airbox is basically just an airbox and not so much a tuning device. The airbox is going the same direction as the fairing, bags, tank, etc.
Anyway the point I’m getting to…. Something that doesn’t always get taken into consideration is float bowl venting. If for example you have a motorcycle that has float bowls that vent into the stock airbox by way of T fittings, tubing, etc and you remove the airbox to install pod filters, it can cause problems if you don’t deal with the vent tube or rejet. Same sort of rule can apply to carburetors that vent into the airbox via other means. When the engine is running, the air pressure inside the airbox, downstream from the filter is lower than atmospheric pressure. The carburetors are jetted to run with the lower pressure, so if you remove the vent hose and install pods, the bowls are subjected to atmospheric pressure. With higher pressure pushing more fuel through the jets, you end up with a overall rich condition and stoichiometric efficiency goes out the window . In some cases this makes the bike almost impossible to ride. Some generally expect engines to run leaner with pods, so having an extremely fat condition can be confusing. Aside from cheap ill fitting pods that block passageways, I’ve come to the conclusion that some carburetors simply don’t like having the rubber boot between the carb and airbox replaced with something foreign. Seems like some replacements create a lot of aerodynamic fungus (sorry love that term) and anything off an idle is compromised. Sometimes removing the boot (which serves as a velocity stack in some cases) from the stock system and installing it in the pod (as shown in a previous post) will make a world of difference. I used to do that when people would bring CB750 choppers into the shop because they wouldn’t run very well with the disgusting looking chrome airbox that they had installed.