Cross wind power loss.

[AJ]

not forgetting the fuel tank is subjected to atmospheric pressure by the vent in the gas cap, which would allow the fuel to flow into the bowls and overcome any pressure lock

Absotively.

But you're a Brit, what do you think of my pixie theory?

[Agemax]

Absotively.

But you're a Brit, what do you think of my pixie theory?

i agree completely. although they would have to be a strong pixie if they were to defy atmospheric pressure.

must be cornish inbreds.............

[posplayr]

not forgetting the fuel tank is subjected to atmospheric pressure by the vent in the gas cap, which would allow the fuel to flow into the bowls and overcome any pressure lock

regardless of all those mitigating factors, float bowl pressure imbalance is probably the biggest cause of any HP loss so equalization is probably warranted. at least do stick any pipe extensions into the airstream.

[Agemax]

so......if you have a vented crankcase breather tank fitted, could you not connect the carb vent pipes to the tank as well? surely there will be next to no fluctuation of air pressure inside the tank !!!!!!?

[posplayr]

so......if you have a vented crankcase breather tank fitted, could you not connect the carb vent pipes to the tank as well? surely there will be next to no fluctuation of air pressure inside the tank !!!!!!?

I was thinking about that but would not want to get the gunk and condensation sucked right into the float bowls.

[Agemax]

I was thinking about that but would not want to get the gunk and condensation sucked right into the float bowls.

it wouldnt suck any gunk if the tubes were attached to the top of the tank, as all the cr@p would settle at the bottom (if you get any into the tank), plus you can get an inline filter to prevent condensation or any moisture from flowing through the pipe......

[Steve]

AJ calls them "pressure equalization tubes", I call them "atmospheric reference tubes", other than that, we agree totally.

Whether you have pods or not, if you run your vent tubes so they end in relatively calm air, like under your seat, there will be no turbulence. The fluctuating pressure in the turbulence plays havoc with the ability of the carb to supply the proper amount of fuel, which affects jetting and mixtures.

3) your bike is inhabited by magical pixies that keep it running properly.

Maybe there's another explanation, ...

..., what do you think of my pixie theory?

i agree completely. although they would have to be a strong pixie if they were to defy atmospheric pressure.

must be cornish inbreds.............

There are no pixies in the carbs, they are GNOMES, as explained in THIS thread.

.

[Agemax]

AJ calls them "pressure equalization tubes", I call them "atmospheric reference tubes", other than that, we agree totally.

Whether you have pods or not, if you run your vent tubes so they end in relatively calm air, like under your seat, there will be no turbulence. The fluctuating pressure in the turbulence plays havoc with the ability of the carb to supply the proper amount of fuel, which affects jetting and mixtures.







There are no pixies in the carbs, they are GNOMES, as explained in THIS thread.

.

haha, so are the coils filled with millions of little spark fairies, with a shocking breeding rate????

[AJ]

AJ calls them "pressure equalization tubes", I call them "atmospheric reference tubes", other than that, we agree totally.

I'm good with that terminology. It's important that the air pressure "reference" is as close as possible to what the inlets to the air filters see, which is why it's better to sample right at the pods than to sample back by the seat when you have pods installed. At least, that's my technical conclusion as I've been experimenting (and learning) of late.

Don't know nuthin' about gnomes except as they work about the garden. Never heard they had anything to do motorcycles!

[gsrick]

There are no pixies in the carbs, they are GNOMES, as explained in THIS thread.

.

I prefer Pixies, as most of the pictures I've seen of them are kinda cute minus the pointy ears, and those can always be bobbed, but Gnomes rub me the wrong way for some reason. Hairy little buggers with stupid pointy hats, hanging out in the garden all the time with those little smirks on their faces. Gives me the willies just thinking about them.


Curiosity got the better of me after reading this and I had to see for my self and find out what exactly was making these carbs work. Sure enough Pixies. I managed to trap three of them and posted them here for all to see.

[posplayr]

I'm good with that terminology. It's important that the air pressure "reference" is as close as possible to what the inlets to the air filters see, which is why it's better to sample right at the pods than to sample back by the seat when you have pods installed. At least, that's my technical conclusion as I've been experimenting (and learning) of late.

Don't know nuthin' about gnomes except as they work about the garden. Never heard they had anything to do motorcycles!

Not sure what you could have tested to confirm this?

Partially based on the link you posted from K&N the design of a Pod is to create a plenum inside of the pod with sufficient surface area to flow the required air for the carb. Basically it is a way of creating an isolated (to an extent) airflow. The large circumference means that a low pressure differential on one side of the pod, will not create a full drop in at the throat of the carb. The Pod will tend to average the pressure that exists around the pod.

On the other hand the port is relatively small and does not average and therefore makes the equalization pressure susceptible to a pressure change wherever you put the end of the tube which is "sampling" the atmosphere.

Probably of more importance (in simplistic terms) the engine is a big air pump and so for a given RPM, the air flow through each cylinder is relatively constant; there is no need to vary the fuel being sucked into the venturi due to differential pressures across the pods.

In other words I don't think that a pressure drop at one pod is going to appreciably affect the airflow through that cylinder, whereas if the atmosphere sample does drop there will be an appreciable drop in the gas flow into the cylinder effectively leaning it out.

(to be absurd, image blowing into the input of a turbofan engine. I don't think it is going to change the flow rate a whole lot as the internal pressures of the flow are much higher that a couple of psi blowing into the input.)

So my conclusion is that this whole effect of PODs losing power in cross winds must really be due to removal of the equalization tubes and not having a equalization plenum that is hidden somewhere under the seat/above the battery box. As Steve said before , it has nothing to do with Pods or not.

I'm thinking of making up a little "pressure equalization" plenum out of copper tubing (see attached). Tubes would be extended just behind the pods with the plenum zip tied to one of the cross braces and the inlet pointed down or back.

I looked at the ESD airbox; it seems as if there is a port in the front assembly (after the air filter just above in carb inlets).

[AJ]

I prefer Pixies, as most of the pictures I've seen of them are kinda cute minus the pointy ears, and those can always be bobbed, but Gnomes rub me the wrong way for some reason. Hairy little buggers with stupid pointy hats, hanging out in the garden all the time with those little smirks on their faces. Gives me the willies just thinking about them.


Curiosity got the better of me after reading this and I had to see for my self and find out what exactly was making these carbs work. Sure enough Pixies. I managed to trap three of them and posted them here for all to see.

Pixies is way hotter than gnomes. Def the way the carbies work.

[AJ]

Not sure what you could have tested to confirm this?

Partially based on the link you posted from K&N the design of a Pod is to create a plenum inside of the pod with sufficient surface area to flow the required air for the carb. Basically it is a way of creating an isolated (to an extent) airflow. The large circumference means that a low pressure differential on one side of the pod, will not create a full drop in at the throat of the carb. The Pod will tend to average the pressure that exists around the pod.

On the other hand the port is relatively small and does not average and therefore makes the equalization pressure susceptible to a pressure change wherever you put the end of the tube which is "sampling" the atmosphere.

Probably of more importance (in simplistic terms) the engine is a big air pump and so for a given RPM, the air flow through each cylinder is relatively constant; there is no need to vary the fuel being sucked into the venturi due to differential pressures across the pods.

In other words I don't think that a pressure drop at one pod is going to appreciably affect the airflow through that cylinder, whereas if the atmosphere sample does drop there will be an appreciable drop in the gas flow into the cylinder effectively leaning it out.

(to be absurd, image blowing into the input of a turbofan engine. I don't think it is going to change the flow rate a whole lot as the internal pressures of the flow are much higher that a couple of psi blowing into the input.)

So my conclusion is that this whole effect of PODs losing power in cross winds must really be due to removal of the equalization tubes and not having a equalization plenum that is hidden somewhere under the seat/above the battery box. As Steve said before , it has nothing to do with Pods or not.

I'm thinking of making up a little "pressure equalization" plenum out of copper tubing (see attached). Tubes would be extended just behind the pods with the plenum zip tied to one of the cross braces and the inlet pointed down or back.

I looked at the ESD airbox; it seems as if there is a port in the front assembly (after the air filter just above in carb inlets).

I appreciate your thoughtful analysis, but am not totally convinced of your conclusions (not necessarily disagreeing, either).

Unfortunately, I don't have a stock ESD airbox to look at. However, on many other bikes, there is no overt "plenum" on the stock setup. The "reference tubes" merely run up near the point where the air enters the airbox, so it's sampling the air at the inlet (while being oriented so that the inlet air is NOT directly drawing across the reference tube endface and the problems that would cause). This is the main reason I'm concluding that the sampling should be done close to the air inlet, but it makes intuitive sense to me.

I wrote "overt" plenum wrt the stock setup because it may indeed be that the top of the airbox, the frame rails, and the bottom of the seat form an "effective" plenum to stabilize and normalize the air pressure in that region. Please post a picture of the ESD setup you described, as it wouldn't surprise me a bit if Suzuki worked to optimize the system. Most stock systems became very well engineered progressing through the 1980's and beyond.

Now, as to sampling near the air filter inlet vice merely providing a point of fairly undisturbed air to sample atmospheric pressure, there are a couple items to note.

Removing the stock airbox and replacing with pod filters drastically alters the airflow up under the seat. In my case, I installed a plastic tool tray covering most of the area where the airbox used to be and then ran the vent tube up under the seat into an area I thought was relatively stable - an "effective" plenum. However, that's no guarantee that the air really is stable up there. Indeed, the disturbed air cascading off the engine may actually be trapped by the side covers of the '82 1100E and be ducting that disturbed air up to the "stable" place up under the seat at higher speeds. It is also no guarantee that the air pressure at that location is similar to what is available at the pods filters.

Airplanes have a big problem with carburetion because they experience huge variation in atmospheric pressure as they climb and descend. The simple answer is that *most* carbureted aircraft use a manually-controlled mixture setting so the pilot can adjust for optimal operation. This is a little bit like manual 'chokes' on our bikes. There are special aircraft "pressure carburetors" that automatically adjust to air pressure, but they are complicated and relatively rare. It would be interesting to look at the mechanisms of their operation.

I mention all this because what is being "balanced" is the differential pressure across the jet (and, if the atmospheric pressure is changing over a wide range, the air density).

I don't think that a pressure drop at one pod is going to appreciably affect the airflow through that cylinder, whereas if the atmosphere sample does drop there will be an appreciable drop in the gas flow into the cylinder effectively leaning it out.

I think that's exactly the purpose of the pods, that they do flow appreciably more air into the engine. (Side note: Everybody thinks you should get better gas mileage from this, but that is incorrect. More airflow means you need more gasoline to maintain mixture, so the engine makes more power instead of providing reduced fuel consumption. Of course, you can "throttle back" to recover some of the lost mileage. These things are much easier to experiment with on an airplane than a road vehicle, but tests - both reported and my own experience - prove this to be true. Optimal efficiency for the vehicle occurs when the engine is operated WOT with minimal restriction, and the engine is sized to make the appropriate amount of power for the application.)

So my conclusion is that this whole effect of PODs losing power in cross winds must really be due to removal of the equalization tubes and not having a equalization plenum that is hidden somewhere under the seat/above the battery box. As Steve said before , it has nothing to do with Pods or not.

I think this is probably correct. I've already noted that my simplistic attempt to make an effective plenum by installing the tool tray was not sufficient. But it is more than simply having a "stable" sampling.

One could conceivable make a sampling port using a ram-air horn in front of the bike, sampling stable, high pressure air, and this would probably fail to maintain the appropriate pressure balance across the jet. Similarly, one could make the sampling location in a nice stable location like, say, up under the seat, but if this proved to be a low pressure area due to air flow (as I suspect it is), then you would again be mismatching the pressure balance across the jet. This is why I think it's best to sample in and around the area where the air is drawn into the filters, not some disconnected location. Sampling at the filter seems logical to maintain the pressure balance across the jet. I further think that either a filter or a plenum (or even an in-line resonance filter) would be a useful addition to stabilize the 'reference' the tube provides.

This is something that is just prime for experimentation because it would be so easy. It would be easy to move the end of that tube around to different locations, adding an air filter, building a plenum, whatever, and observing the effects. Getting more sophisticated, one could add some electronic sensors and a data logger. What fun!

But, alas, if my immediate problem is solved by removing the damned tube running up under the seat or placating my carburetor pixies (I have started leaving a cookie on the starter cover when parking my bike), then I will move onto more immediate projects, such as painting my forks, rebuilding the headset, polishing the swingarm, getting a fairing, and maybe retrofitting modern brakes.

Offered in the respectful tradition of technical discussion.

[AJ]

P.S. This is my first bike with pod filters, and it came to me that way. Personally, I think installing a free-flowing filter into the stock airbox would be a better way to go, but it just wasn't worth the extra investment to find a stock airbox, plus I do like the look and convenience of the pod filters. It's very hard to improve on the stock design and it's not at all clear that the pod filters are really superior in the real world. They may show improvements on the dyno (usually pretty negligible, btw), but a bike on a dyno is not experiencing the turbulence associated with running along the highway at 70 mph. Putting those pod filters directly behind the engine has to be one of the worst places to pick up your air - the air flow is turbulent and the air has been heated by the engine.

[Agemax]

well i am just going to leave mine as it is, vent tubes removed completely. it runs fine and i am happy with it.

if it makes any difference at all, i have a stainless plate mounted covering the gap in the frame where the air box used to sit. whether it helps or hinders, i dont care, it looks nice