Reduce Pod Air Flow vs Rejetting

[Guest]

When I bought my 81 GS850 last year, it already had a 4-1 exhaust and pods on it. I've read many of the threads on here about the difficulty, and time consuming process of rejetting the carbs to get the bike running properly.

Does anyone have an opinion on modifying the filters to reduce air flow (approximately) back to stock air flow as opposed to rejetting? It seems to me - this may be wishful thinking - that it would be easier to calculate the stock rate of air flow, and adjust the pod air flow to a similar CFM than the process of removing the carbs, adjusting the jets, replacing the carbs, rinse and repeat numerous times...

Thanks in advance.

[Nessism]

I've seen this done using a sleeve that fit inside the pod. More holes in the sleeve means more air and visa versa. Worth a try I suppose, but not as good as the stock airbox.

[Steve]

I think you will be putting in at least as much time and effort trying to tune the airflow for the available fuel as you would to tune the fuel flow for the available air.

One possibility reduces many of the variables and unknowns, get a Dynojet Stage 3 kit. Yeah, it will cost a bit of money, but it's pretty much a "buy once, cry once" type of deal. For all the time you will spend tuning the number of holes in multiple sleeves over the pods, ... well, let's just say that it's a good thing that your time is cheaper than a dealer's time.

.

[gsrick]

When I bought my 81 GS850 last year, it already had a 4-1 exhaust and pods on it. I've read many of the threads on here about the difficulty, and time consuming process of rejetting the carbs to get the bike running properly.

Does anyone have an opinion on modifying the filters to reduce air flow (approximately) back to stock air flow as opposed to rejetting? It seems to me - this may be wishful thinking - that it would be easier to calculate the stock rate of air flow, and adjust the pod air flow to a similar CFM than the process of removing the carbs, adjusting the jets, replacing the carbs, rinse and repeat numerous times...

Thanks in advance.

You can try that or get the Dyna kit. Usually the jetting for pods and a 4-1 is around three sizes above stock. It is recommended to get a size below and a size above three sizes up. Since you have pods and not an air box, it's not that hard to experiment with jetting and needle height, since they come off and go back on much easier than with the air box in place. The hardest part is hooking up the linkage.

[Steve]

The hardest part is hooking up the linkage.

If that is the hardest part, the rest of it must REALLY be easy.

Rick, do you not hold the throttle open with one hand (or a small screwdriver handle) while you put the cable into the pulley?

And, of course, that is before you slip the carbs into the intake boots.

The "choke" cable doesn't matter too much when it gets connected.

.

[mmattockx]

Usually the jetting for pods and a 4-1 is around three sizes above stock.

It will be way more than that. MY 1100E stock mains are 107.5 and I am currently at 142.5 with APE pods and a Kerker canister 4-1.


Mark

[Agemax]

It will be way more than that. MY 1100E stock mains are 107.5 and I am currently at 142.5 with APE pods and a Kerker canister 4-1.


Mark

very true, the mains that come with the DJ3304 kit for the GS1000 VM carbs are 138 and 142, roughly 130 and 134 Mikuni equivalent. Stock mains are 95.

[RichDesmond]

When I bought my 81 GS850 last year, it already had a 4-1 exhaust and pods on it. I've read many of the threads on here about the difficulty, and time consuming process of rejetting the carbs to get the bike running properly.

Does anyone have an opinion on modifying the filters to reduce air flow (approximately) back to stock air flow as opposed to rejetting? It seems to me - this may be wishful thinking - that it would be easier to calculate the stock rate of air flow, and adjust the pod air flow to a similar CFM than the process of removing the carbs, adjusting the jets, replacing the carbs, rinse and repeat numerous times...

Thanks in advance.

It won't work, at least not well. The difference between pods and the stock setup isn't just total flow. The airbox acts as an accumulator and smooths out the pressure variations on that side of the carb. That changes the balance between the low speed and high speed circuits on the carb.

[scratch]

Pod appologists will protest but, 2 other items of note.

1. "Rate of flow" is not the only issue. Please don't forget the role of the piston slide vacume chamber...
That slide is supposed to start moving up at about 1/4 throttle to keep everything working right and air pressure in that top champer is important to any opperation from 1/4 throttle up. Open air flow to the slide vacume chamber creates an entirely new dimention of issues for a CV carb Solution? Factory Airbox.

2. the factory airbox is also important to keep your carbs stable as, they hold the rear-side of the carbs in place. When you hit bumps or just bike vibrations the carb rack moves... the weight of your carbs hanging on just those intake boots causes movement that was not planned for when they designed the intake boots. If they had, perhaps they would have made them thicker or added a brace? Have seen a podified carb rack move up an down from a poor/hacked trottle cable set-up. Movement and added oscilations will effect fuel level in your float bowls and wear-and-tear on intake boots... So, at least find a way to add additional bracing. It will help a little, if not imediately it will in the long run by slowing intake boot failure.


Propperly cleaned and tuned carbs carbs with a correct airbox & functioning ignition is, at the end of the day the easiest and cheapest way to go unless you have a free dyno, boxes of jets and infinate time on your hands imo.

Try starting with a good airbox to figure out what you need to re-jet for for the 4-1. That will be much easier and create a lot of improvement. Plus it will help you achieve jetting/tunning knowledge and experience in smaller bites, rather than re-engineering a a whole fuel system without previous tuning knowledge. Small changes from stock, record data, adjust etc...

Now... as I am probably p1$$ing in the wind, back to the stage 3 recomendations.

[PardonMe4687]

Thank you all for your insights. It seems the ideal course of action would be to revert back to the factory airbox. We'll see if I can track one of those down for a reasonable price, which of course will mean getting new carb boots as well. At the end of the day, it seems like that might be a more expensive route to go as opposed to going with a Dyno carb kit, or 6sigma carb kit.

As I said in my original post, it may have been wishful thinking... and it turns out it was.

[mmattockx]

Pod appologists will protest but, 2 other items of note.

I wouldn't say I am an 'apologist' for pods. My experience with them has been very positive, but not everyone will agree. One thing to note is that the 16V 1100's seem to take to pods and a 4-1 exhaust pretty well while the smaller bikes (especially the 550's) seem to be much harder to sort out. The big bikes certainly don't take a dyno, giant piles of jets and endless time to get working well, but they do require the tuner be methodical and proceed in a step by step fashion. Most people who fail in their tuning attempts don't follow those simple rules and the end results speak for themselves. Personally, I had the carbs off my 1100 ~7 times in the initial tuning and then once more when I changed to the APE filters to adjust the needle to suit them. It now runs at least 99% as well as with the airbox and makes significantly more power in the process.

Thank you all for your insights. It seems the ideal course of action would be to revert back to the factory airbox.

I wouldn't say the stock airbox is the 'ideal' solution, but it certainly is the easiest and most predictable way to go.


Mark

[gsrick]

If that is the hardest part, the rest of it must REALLY be easy.

Rick, do you not hold the throttle open with one hand (or a small screwdriver handle) while you put the cable into the pulley?

And, of course, that is before you slip the carbs into the intake boots.

The "choke" cable doesn't matter too much when it gets connected.

.

I have forgotten sometimes to put it on before I put them back in the boots. My point is when you have pods it's really easy to change jets.

[dorkburger]

Another thing to keep in mind... even with the stock airbox in place, some adjustment will likely still be needed due to the exhaust, albeit smaller ones.

[Nessism]

Ripped from KZ Rider, as posted by a very knowledgable guy...








Cut and paste...

"My reasons for switching to pod filters was for many reasons:
1. I was to inexperienced to know better.
2. My airbox boots were hard as a rock. When removing or installing my carbs when I first tried to get it running was a nightmare. I even knocked the bike off the side stand onto myself trying to wrestle the carbs on the boots once.
3. I found the K&N filters on Amazon for a third of the price of new airbox boots.

The first thing I did was purchase a Factory-Pro stage 3 jet kit (negating the savings of the air filters) and installed it according to the directions they listed for pod filters and a stock exhaust. Around town was fantastic. Any speed above 60mph it was unridable.
The issue that people time and again state, is that CV carburetors must not have any positive air pressure going into the intake side. When the carb has air forcefully blown into them rather than the carbs drawing in air at their own “pace”, the vacuum diaphragm controlled slides shoot up and dump to much gas into the engine causing it to bog down. Pod air filters flow to well and allow to much cross wind air into the carbs and at high speeds the air is actually forced into the cabs like you were pointing a leaf blower at them.
My first solution was to wrap my filters with vacuum filters. As described in this thread:

https://www.zephyr-zone.com/cgi-bin/yabb2/YaBB.pl?num=1349470533/6#6

Last spring, the vacuum filters did not survive me removing them for cleaning, so I had to come up with a new solution. This time I made baffles to go inside the pod filters themselves to “shelter” the carbs intakes (where the vacuum intake for the slides are) from the onslaught of air coming in. I got the idea from some people using velocity stacks inside of pod filters to redirect the air coming in.
I made the baffles from the cans of the beer I was drinking at the time when I got the idea.
They were incredibly easy to make using only a pair of scissors, rivet gun and a single-hole paper punch. I made the length of the baffle so it starts at the mouth of the filter and seals tightly against the rubber back end of the filter, so the air has to go through the holes and can’t rush in the end of the baffle. I made sure to punch enough holes in the baffle so as not to starve the carbs of air and my unscientific tests I did showed no restriction in flow rate between a baffled and un-baffled filter.
The baffled filters work flawlessly with the Factory-Pro jet kit and It pulls hard from idle to redline and cruises smooth as glass no matter how fast I’m going."

I needed to drink the beer as fast I could so I could use the empty cans to make the baffles, so by the fourth can my craftsmanship was really starting to suffer. (that is the one pictured.) I was doing really unscientific tests with using a vacuum cleaner to suck air through the filter with and without the baffle. When the vacuum stopped struggling and was using the same amount of "effort" to suck air through the baffle as the it did without it, I stopped punching holes in the baffle. I wanted just enough resistance to stop the "cross wind effect" but to not starve the engine of air.
It works, but velocity stacks area more elegant solution to the cross wind issue. But they are way more expensive than a 4-pack of Murphy's Stout.

[RichDesmond]

That's interesting, but a very different goal than what the OP had.