Pod filters

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Folsoml
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Pod filters

Postby Folsoml » Thu Feb 28, 2013 1:12 pm

Let me see if I understand the problem with pod filters. The stock carbs are tuned/jetted to allow a perfect mixture of fuel and air if the bike is fitted with the standard airbox filter system. When a person adds pod filters, they allow too much air for the standard jets, requiring the carbs to have larger jets installed to get the correct ratio.

I'm sure someone will correct me if I am misunderstanding what is going on here, so I'll get to my question: Since pod filters are so popular for people who want that cafe racer look, has any company ever tried to make a pod filter that mimics the air flow of the air box, thereby allowing them to be used without a rejet?
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Lejaun79
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Re: Pod filters

Postby Lejaun79 » Thu Feb 28, 2013 2:48 pm

I have the same problem, I want to put pod filters on my bike, but don't want to go through all the trouble of re-jetting the carbs.
If there is such a company that supply such pods, please let me know too.

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Volker_P
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Re: Pod filters

Postby Volker_P » Fri Mar 01, 2013 6:05 am

Many cafe bike guys have pod filters just for the look.
Originally, they were intended to leave through more air avoiding all these hoses and cases and whatever for more power (in of course carefully rejetted carbs).
So far I am not aware that they make pods for people that only want to look faster.

I agree this is a bit surprising as obviously the market is there! :lol:
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Mainerider
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Re: Pod filters

Postby Mainerider » Fri Mar 01, 2013 7:44 am

Folsoml wrote:Let me see if I understand the problem with pod filters. The stock carbs are tuned/jetted to allow a perfect mixture of fuel and air if the bike is fitted with the standard airbox filter system. When a person adds pod filters, they allow too much air for the standard jets, requiring the carbs to have larger jets installed to get the correct ratio.

I'm sure someone will correct me if I am misunderstanding what is going on here, so I'll get to my question: Since pod filters are so popular for people who want that cafe racer look, has any company ever tried to make a pod filter that mimics the air flow of the air box, thereby allowing them to be used without a rejet?



An airbox serves many purposes and one of the most mportant is to supply the carbs with a consistent and steady reserve of STILL air. Under most conditions, pod filters can't offer this; they are affected by turbulence from several sources, including cross winds, the rider's body, and the bike itself . Air pressure is directly related to air speed and carbs have a hard time dealing with the constantly varying vacuum pressures that pods often cause. This varying air speed problem occurs on even a single-cylinder bike; the problem only increases on multi-cylinder bikes. Each pod is essentially its own air supply system; with potentially varying air speeds (hence varying vacuum pressure); at each pod (due to varying turbulence levels), you will have an issue that mimics that which occurs when one or more of your carb intakes has a vacuum leak: erratic idling, stumbling, surging, etc.

This is one of the reasons that a lot of pod-equipped bikes suffer from surging problems; even after re-jetting, the lack of consistent vaccum pressure causes fuel flow to ebb and flow.

We haven't even touched on the problems of pods while riding in rainy weather...

In summary, in certain situations pods can be beneficial but overall, for street riding, they cause more problems than they cure. Pods look cool, they make carb removal and install much easier, but they are inferior to a well-designed air box. The manufacturers in the 70s and 80s weren't stupid, their marketing departments knew even back then that people loved the look of pods and if they could have fitted the bikes with pods without adversely affecting performance and ridability, they would have; they didn't because an airbox serves several important roles that pods can never handle.
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Folsoml
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Re: Pod filters

Postby Folsoml » Fri Mar 01, 2013 1:49 pm

Very nice, Maine! Thanks for all that!
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M_Hills
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Re: Pod filters

Postby M_Hills » Sat Mar 02, 2013 7:41 am

Why do they have to look so cool?!
I'm guessing that velocity stacks are even worse?
A project bike is very revealing..... like for example..... I've come to realize that every time I project how long something will take, I need to just double it...... I'll then be about 1/2 way there!

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Re: Pod filters

Postby Mainerider » Sat Mar 02, 2013 4:37 pm

Trust me, I wish pods were a good idea, too. After struggling mightily last night to get a carb rack reinstalled on an '87 ZL1000 Eliminator, i went to hook up the push and pull cables onto the throttle grip only to find that the customer-supplied, custom-made cables ( the OEM cables are no longer avail for this 2 model-year bike) were built too short...Arghhhh...

Off came the carb rack I had just got done busting my nutz getting on ( unlike some bikes, getting the throttle cables on these carbs after they are on the bike is impossible) and back into the box went the throttle cables...

Good times... Good times...
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pabs11
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Re: Pod filters

Postby pabs11 » Tue Jun 18, 2013 1:02 am

AWWEEE MAN!!

I feel like my dreams have been pooped on reading this thread :cry: . If you had no choice to go with carbs for a 79 cb650, which one would be best? Also should i stay away from the cheap ones?

I love the cafe racer look, Sorry :(

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JorgenL
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Re: Pod filters

Postby JorgenL » Wed Jun 19, 2013 4:22 am

Well I've been running stock air-box then Emgo-pods and now I'm putting on velocity stacks.

The main reason I went pods was to get rid of the bulky airbox contraption and to make carb removal easier.
My goal was to get stock performance or better.

My bike is not a commuter/daily driver bike and will not be driven in the rain (if I can avoid it, although it has happened).

It is possible to get a 80 pd51a slide carb to behave with pods or stacks. Not saying it's easy, it takes some fiddling and testing, my carb rack has been on and off maybe 10 times when I installed pods.
One: Never put pods on a bad running bike. Only attempt pods on a bike that runs perfectly with stock setup.
Two: There is no dead on recipe on how to jet them. Every bike is slightly different. But you can get a good starting point.
In my case I had to open up the exhaust just a little bit to get into the sweet spot, before that it was a bit jerky at 3000 rpm in higher gears.
I removed the baffle and made a lid that could be screwed on and adjusted with washers. Just like the supertrapp mufflers.
Three: Check your plugs, check your plugs, brush them off, take a looong ride. Check the plugs again. Repeat.

One interesting observation is that when put header wrap on the tubes, my plugs went from tan to white. So this small modification affected the mix, making my engine lean. I didn't even take the headers off when I installed the wrap.
When I talked to a local engine builder he said that the wrap increases exhaust velocity.

Some people need to shim the needles to get it running ok, I didn't have to, mine are still in the middle position.

Also syncing the carbs seems to be more noticable when running pods. Eyeballing the synch is not enough. I used a metal rod as feeler gauge to get them even and to get a good starting point.

I'm experiencing smooth acceleration, from 0 to red. Slightly better throttle response than stock. Easier start, less running with choke, tan plugs.
I have had a few cb750 and 650 owners take it for a ride just to confirm that is not just in my head it runs right.
A friend of mine put a plastic tube inside his pods, extending the intake all the way until it hit the inside wall of the pod. It corrected his driveability problems.

I'm not saying it's for everyone but it is doable.

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Folsoml
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Re: Pod filters

Postby Folsoml » Wed Jun 19, 2013 4:52 am

Image

This is a 77 Suzuki that belongs to a buddy of mine. He made an airbox out of PVC pipe and installed three pods on it. He says it gives him the best of both worlds. I wish I had a better picture of his set up. Has anyone seen something like this before?
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JorgenL
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Re: Pod filters

Postby JorgenL » Wed Jun 19, 2013 7:09 am

Folsoml wrote:This is a 77 Suzuki that belongs to a buddy of mine. He made an airbox out of PVC pipe and installed three pods on it. He says it gives him the best of both worlds. I wish I had a better picture of his set up. Has anyone seen something like this before?


I've seen a couple of PVC pipe solutions but none with an airbox like that... very clever!

I have seen a couple of velocity stacks that end up in a filter box.
Like this one, although I'm not sure there are full tubes internally: http://www.steeldragonperformance.com/images/IMG_0231.JPG

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Volker_P
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Re: Pod filters

Postby Volker_P » Thu Jun 20, 2013 1:32 am

JorgenL wrote:One interesting observation is that when put header wrap on the tubes, my plugs went from tan to white. So this small modification affected the mix, making my engine lean. I didn't even take the headers off when I installed the wrap.
When I talked to a local engine builder he said that the wrap increases exhaust velocity.


Does anybody know the physical facts behind that?
Because I would have no problem to understand that a wrapped exhaust would reduce exhaust speed (gases viscosity is ~SQRT(T)) and reduce cooling in general so the engine/head just would get hotter which would also rise plug temperature which would make them look brighter.
But I see no reason for a contrary effect on exhaust gas speed or a way to relate that to leaner conditions.
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JorgenL
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Re: Pod filters

Postby JorgenL » Thu Jun 20, 2013 10:59 am

I always thought that hotter gasses decrease in density taking less space and because of that the total flow increases.
I dont think the speed of the gasses would be affected much.

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Re: Pod filters

Postby cb650 » Thu Jun 20, 2013 10:28 pm

The speed dont but there are less gases to do the work. A pilot may have to use a air density chart to figure takeoff distance for altitude and temp.
Less gases (air) over the wing less lift. Plus the less oxygen lowering the HP.
Did you clean the tank out?!?!?!?!

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Lejaun79
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Re: Pod filters

Postby Lejaun79 » Fri Jun 21, 2013 2:15 am

I've head a story about the air density, but that is all past the exhaust valve stage, in my mind I think the air less dense hot air will travel much more freely through the exhaust system and as far as I know that will help with increase HP at high revs. Honestly I don't think it will make such a difference, but it looks cool.
My only concern is adding heat to the aircooled engine because the heat can't escape to your pipes.


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