Rejetting and Pod Air Filter questions

Got a couple questions about pod air filters for anyone that can answer them.

I've got a 1985 XJ700N, standard in-line four, stock pipes, stock carbs. I want to remove the air box and put on pod air filters. Has anyone done this to their bike and would anyone recommend it? I know I need to re-jet my carbs but I don't know how much bigger/smaller I need to make them.

If anyone can tell me how to do the math and if this process is worth the money any help would be greatly appreciated.

Thanks,
rubikscube

 

WHAT ABOUT RE-JETTING FOR PODS, ETC?:

It's a question we get asked often and unfortunately, one that we cannot answer honestly about your specific bike besides with "it depends".

Which is a nice way of saying "you're about to enter the seventh circle of hell......."!

Carb jet tuning required by aftermarket modifications is somewhat of a black art, part science, part skill, part luck. It depends on the current state of tune of your engine, your altitude, the mix of aftermarket parts on your bike, etc........a lot of variables.

The best advice we can offer is: Just Say No. Don't do it! Leave everything stock!

But, since most people---with good reason, I might add---don't always listen to our well-intentioned advice, then the next best recommendation we can offer is: "if you want more power get a bigger bike!".

And since that doesn't cut it with many owners, either, for the remaining stalwarts out there who insist on "experimenting" with aftermarket intake and exhaust systems, here's the best information that we've come across to give you some GUIDANCE, which you should take as just that, and not as ANSWERS, because it isn't!



MAIN FUEL JET SIZE CHANGES NEEDED PER TYPICAL MODIFICATION:


Typical Exhaust Changes:

+2 main fuel jet size for custom 4-into-2 exhaust

or

+4 main fuel jet sizes for 4-into-1 exhaust

or

+4 main jet sizes for no muffler (open headers)


Typical Intake Changes:

+2 main fuel jet sizes for single K&N filter (inside a stock airbox)

or

+2 main fuel jet size for drilling holes in the airbox with stock filter

or

+4 main fuel jet sizes for individual pod filters (no airbox)



Additional changes:

- Add up all the main fuel jet size increases and subtract 2 sizes.

- Decrease main fuel jet size by 2 sizes per every 2000' above sea level.

- Under a mis-match condition, such as when using pod filters with a 100% stock exhaust, or 4-into-1 header with stock filter and air box, then subtract 2 main fuel jet sizes.


PILOT FUEL JET SIZES CHANGES NEEDED PER TYPICAL MODIFICATION:

Pilot fuel jet size changes are related only to the change in main fuel jet sizes according to the main fuel jet size formula described above. Note that this pilot fuel jet rule is for the main fuel jet size change BEFORE any main fuel jet altitude compensation is factored in:

Increase the pilot fuel jet size +1 for every +3 main fuel jet size increases.

Additional changes:

- Decrease pilot fuel jet size by 1 for every 6000' above sea level.



PRECAUTIONS:

- Make sure your carbs are in perfect working order before making jet changes....meaning fully cleaned internally and rebuilt, operating properly in their stock configuration, proper sized air jets and needles, etc. Otherwise, you'll like find that all of your efforts are going to be a HUGE waste of time.

- Check plug color often and adjust as needed, 2 main fuel jet sizes at a time and 1 pilot fuel jet size at a time. Bright white plug insulators are a sign of an overly lean fuel mixture condition and WILL cause damage to your engine over time, up to and including engine seizure!

- Synch the carbs after each jet change.

- Make sure the floats are set correctly

- Seriously consider purchasing a Colortune Plug Tuning kit.

- You may find it necessary to make changes to the size or shimming of the main jet needle. There are no guidelines on what or how to do these changes, this is true trial-and-error tuning!



EXAMPLE:

A 1982 XJ550RJ Seca using an aftermarket Supertrapp 4-into-1 exhaust and a single K&N air filter in the stock, unmodified airbox. Bike is primarily operated at an altitude of 2600 feet above sea level.

XJ550 Seca Stock Mikuni BS28-series Carb Jetting:

#112.5 Main Fuel Jet
#35 Pilot Fuel Jet
#70 Main Air Jet
#170 Pilot Air Jet
4GZ11 Needle


MAIN FUEL JET SIZE CALCULATIONS:

Changes made:

Exhaust:
4 into 1 with Supertrapp = +4 Sizes Main Fuel Jet

Intake:
K&N Pod Filters = +4 sizes Main Fuel Jet
----------------------------
Equals: +8 main fuel jet sizes above baseline
Subtract: -2 main fuel jet size per formula above
----------------------------
Equals: +6 main fuel jet sizes due to modifications, thus:

Stock main fuel jet size is: #112.5
+ 6 additional sizes
= a #118.5 main fuel jet size
---------------------------
Subtract: -2 main fuel jet sizes for Altitude of 2500' Average

= #118.5 calculated from above
-2 jet sizes for altitude adjustment

= a #116.5 main fuel jet size.


PILOT FUEL JET SIZE CALCULATIONS:

The formula is: +1 pilot jet size increase for every +3 main jet sizes increased.

Stock pilot fuel jet size is: #35
+ 2 additional jet sizes (since we went up +6 main fuel jet sizes before the altitude compensation was factored in):

= a #37 pilot fuel jet size.

Note that no altitude compensation is needed on the pilot fuel jet since our elevation is less than 6000' a-s-l.


------------------------------

RESULT:

A #116.5 Main Fuel Jet and #37 Pilot Fuel Jet is A GOOD STARTING POINT.

******************************************************

Note that the above calculations do NOT take into account any possible changes in the sizes of the air jets nor the main needle size, which are additional variables and opportunities for tuning excellence (or frustration!).

For further insights and understanding, the Holy Grail (meaning: the whole miserable, un-varnished truth of what a real chore carb tuning is going to be, written by people who actually know what they're talking about, rather than by people who are trying to sell you something) can be found at:

www.factorypro.com

and then click on the "Product Support/Technical Support" link at the top of the page, then on the "Motorcycle Tuning Tech" link, and then the "CV Carb Tuning" link........and then read, weep, study, and do....if you still dare to! HINT: if reading through it makes you think to yourself "sheesh, this sounds like an incredible amount of effort!", well, you're right! That's just some of the joys (and pitfalls) of getting to play "tuning engineer", which is what you're going to be doing. Yamaha probably has 10 of those types of guys on staff, and millions of dollars of test equipment, both physical and computer-aided, that allowed them to get the mixture settings just right---from an overall drivability AND power output standpoint----and now, since you're changing the airflow parameters thru the engine, you'll have to figure it all out "from scratch", but WITHOUT the benefit of 10 trained engineers and all that test equipment and experience.

That's why we warn you that setting up a bike for pods can be quite a bit of trial-and-error procedure. You can make the calculations according to what is shown in that guideline and then order the jets that the "formula" recommends, and that should serve as a good STARTING POINT............you may (or may not!) have to do more tuning and trial-and-erroring substitution of different jet sizes, etc. to get it performing to you satisfaction, with the recognition that you may ALWAYS end up with a situation that has some kinds of trade-offs.....lazy at the lower end but runs well at mid/upper-ranges, or runs well at the lower end but a "flat-spot" at some other rpm range, etc. Unfortunately there is no magic formula........you might want to read through the factorypro.com article that I list at the end of that section, and you will get a better understanding of what is involved to get the carbs set-up properly in a non-stock configuration.

 

Never done it. I say don't from everything I have read unless there appears to be a problem with the way the bike is running now.

 

I looked up the Airbox v.s. Pods question with the Radian YX600 Yahoo user group (XJ series engines are nearly identical, same carbs etc). Like myself, a few of their riders have Pod Air Filters - big mistake. According to all accounts pods aren't worth all the trouble to re-tune because the trial and error carb re-jetting process involves so many compromises it destroys much of the engine's goodness; it's power, flexibility and torque.

I can tell you my bike has a much narrower power band now and has lost a lot of driveability. Why? The xj550 has great all-or-nothing throttle response and not much low end smoothness. It has great acceleration, strong mid-range punch and then power falls off quickly at 5,000 rpm just when you need it. At 55-60 mph the engine falters and loses power while attempting high speed passing. Not the best behavior on the freeway.

In common with my experience; in tests, Pod-equipped xj bikes actually LOST horsepower. So my goal is to replace the stock xj550 airbox via cutting the left side vertical frame member and installing 2 GP style tube joints to allow easy oem airbox access. Then, and only then, will a K & N single airbox filter be used inside along with the stock exhaust. Otherwise the engine has to be pulled.

Then there's the question of valuable time lost; e.g. spent fiddling, fixing, "re-tuning" for very little, if any, gain.

It seems Yamaha engineers (with GP racing experience) knew what they were doing when they designed & tuned the factory engine and it's sub-systems. Leave the pods to those gentle souls who still use rural mailboxes for air cleaners on aging ponycars.

 

I'm sure the right engineer could figure-out how to regulate the Intake Air to make Pods work.
I couldn't supply a Brainiac Math Wizard with the first critical factor.
Cubic Feet per Minute drawn-in at the Airbox Atmosphere Inlet.
The key is managing CFM.

Limit CFM
Accelerate Airflow into Carb Intakes
Adjust Main Air to optimum for A/F Ratio.
Complicated.

 

Damn, didn't know it would be that confusing, and a pain in the ass. I think I'll stick with the stock air box.

 

Leave the stock airbox if you can. Like taildragger said you'll get better preformance from a K&N style filter and the stock airbox. A 4 to 1 header and exhaust will improve power also. I have worked on several bikes with pod filters, they are a nightmare to tune and it is nerver quite right.

 

The optimum word being ... "Never"

 

+1 on replacing the stock airbox. As for cutting the frame, it almost might be easier to bite it and pull the motor once. I'm facing the same dilemna, my nearly 100% original stock '81 550 Seca's airbox is literally coming unglued at the seams, and I have a replacement, HOWEVER... there's that "pull the motor" thing...

As for rejetting for exhaust OR airbox mods, it WILL be necessary. I agree with the majority here, leave well enough alone unless you REALLY THINK you can out-engineer the Yamaha engineers who designed the thing.

 

Despite all the warning from people who've never done it, installing pods and is entire doable. The key is patience because there is no exact formula. I recently converted my 83 XJ900 Seca and it runs real sweet, sounds great. Also, I found that the formula provided in this thread left my bike too lean. I asked around on different forums, websites, mechanics, etc and here's what i ended up with.
MAIN JETS from stock 107.5 to 122
PILOT JETS from stock 37 to 44
IDLE JET - 4.5 turns from lightly seated.
That's with a 4-into-2 exhaust system- made up of stock headers and Cobra F1 stainless steel end cans.
NEEDLE JET- Clip on lowest setting, raising needle to highest possible of 3 positions. (which means more fuel is flowing into the carb)
Once converted to pods, the bike takes a bit longer to warm up because the exposed pods get colder more quickly so don't worry if that happens.
The patience part was all the plug chops I had to do at different throttle settings. Cutting the engine at a certain rpm in a certain gear then rolling to a stop to check the condition of the spark plugs. I had to do this in every gear at different rpms and make minor tuning adjustments. Eventually I ended up with good progressive power in every gear with no flat spots.
At least the jets are cheap so you can try different combinations without spending too much.
Also, make sure your valve shims are within spec before starting any modifications. So don't be scared off by all these dire warnings from people who've never tried it. Oh, and don't forget to spray the filter pods with air filter oil every so often. That helps keep the dust and smaller debris from getting into your carbs and engine.
and one more thing, make sure your carbs go "CLUNK" as Rick'o'Matic says. If the diaphram isn't rising and falling properly, then nothing else will work.
If after everything else you're still running lean, you can try shimming the needle jet if it doesn't have clip positions to move it up or down. That's the big main needle in the middle of the carb body.
Good luck.

 

Well, ... first of all ... the Huge Mikuni's Yamaha puts on the 900 aren't in the same boat with anything else other than what's on the 900.

Everybody else, with Hitachi or small Mikuni's, can't match how the BS-35's on the Seca 900 can be tweaked. They're close to being Race Carbs. Close; No cigar.

I have heard a few stories and even read some remarks from Members on this Forum that say they have Pods, Pipes and what-not and their bike is running great. I don't know what they consider great. So guys are happy to have the bike start and stay running. To them; that's great. Tweakers need to have the bike on-the-money. A bike that will Idle at 900 rpm while you dig-around in your pockets for Highway Toll money. Then, leave the Toll Booth and accelerate right up to the Red Line without any sort of lag or discrepancy in the transition from Idle to Wide Open Throttles. Full power on demand.

To make an XJ Bike run perfectly; you have to hit mixture parameters of Air~Fuel Ratios within a Plus-or-Minus percentage that is expressed in very low figures.
Without considering VELOCITY.
Without considering TURBULENCE.
The most important factor to achieve within a tolerance of Plus-or-Minus 10-Percent or LESS ... is: Cubic Feet Per Minute of Intake AIR.

Successful Tuning is reliant upon a precisely limited Total CFM divided by 4.

 

Gee. Kinda like my 550. The point here is that a bike that runs as Rick describes above is much EASIER to get to within the parameters of the stock airbox/exhaust. It CAN be done "on your own" with pods and/or aftermarket exhaust but it will take a long time and YOU may never get there, others might. Problem being, it's uncharted territory. For those of us with the stock parts, Yamaha did all the difficult work for us. All we have to do is get it back to how they had it, we don't have to re-invent the wheel. And sometimes that is difficult enough.

 

I pulled the motor on my first Seca 900 in 1984 when I was 21 and had almost NO tools. I bought a Craftsman OPEN metric wrench set and a vice grip. Pulled the motor outside, in the dirt. My labor saved me $200 on fixing 2 nd gear. I put the motor in, and forgot the bellows, so I pulled it again!

So no excuses on pulling your motor.

My current 900 has a factory airbox riddled with 20 quarter inch holes, and a 4 into 1 exhaust. I haven't peeked in the carbs yet for jet sizes. At large wrist angles it will show an occasional flat spot, then surge. But it returns 49 MPG, idles smooth, and has never let me down. I'm happy.

 

So YOU'RE the guy... The reason I put pods on my XJ900 is because when I rescued it from sitting outside in a salvage yard for several years, I found the airbox was badly cracked in 4 different spot- AND some PO had drilled a few dozen 1/4" holes in it. When I tried to shift the airbox to get the carbs out for a rebuild, a piece of the airbox came off in my hand. That how I found out about all those cracks and holes. I was thinking of trying to refurbish it somehow and I still might- I kept all the broken bits and pieces. In the meantime, I couldn't find an airbox and Yam wants $379. for one. So I was forced to improvise and went through the somewhat enlightening hell of tuning a set of pods.
I took a lot of time and curse words but the bike now idles at 1000rpm with no hiccups. It bolts off the line and has good low down power but its once you reach 5000rpm that the banshee awakes and it jumps into overdrive. Kinda scary, actually.
Chores that had to be done:
Cleaned and rebuilt carbs (thanks to RickOmatic for many tips)
Rebuilt the forks and anti-dive units. (thx to Tom at Cyclewerx Toronto for advice)
Rebuild front and rear calipers and new brake lines (thanks to Marc at T.O. Cycle for parts/advice)
Rebuilt master cylinder.
Converted cacked fuse box to blades with 12 gauge wire (thanks to RickOmatic tip sheet).
Installed tail rack (thx to Rich DeZago)
Sprayed with matt black tremclad - using shop spray gun (thx to Gino & Mike at New LIfe Autobody, Toronto)
Replaced broken shifter return spring.
Replaced clutch plates.
Carefully cleaned exhaust ports with dremel (after stuffing rags down exhaust holes)
Replaced final drive hypoid oil.
Cleaned header pipes and collector box but endcans were shot, replaced with set of F1 Cobra stainless endcans from Honda V45 Sabre.
Checked and replaced a few valve shims.
Plugs/oil/filter.
Installed missing headlight/surround (thx to RickOmatic}.
Replaced wheel bears (thx to Rich DeZago).
And big thanks to Rich DeZago for the beautifully spiral bound factory service manual and parts book).
Left to do:
Install set of Bridgestones (the Avons on there now are pretty bad)
Purchase and install EMGO shocks (thx to this forum for tip on crc2onlinecatalog.com website).
Install mini-indicators front and back.
Much polishing of wheels, rearsets, etc.

Yes, it's been a labor of love and I couldn't have done without this forum and the great folks who make it up.
thanks again to everyone.

 

Oye...what a fascinating thread.

Yeah.. I really wish I could put a stock airbox in without pulling the engine. Ok...people cut them up to remove them. Could you cut one in 2 pieces and reassemble it inside the frame? Or are 2 pieces still too big?

Man...I'm going to end up trying a lot of jets on my 750 Seca if I keep these damn pods. :roll: Well..with a colortune plug, it should be easier.

I'm guessing that K & N pods allow more air vs. the stock filter. Couldn't you make the pods more restrictive (I know that sounds crazy) to more closely match the paper filter?

For instance, if you've inherited a bike with pods, wrap the pods in Scotch foam to reduce the CMF a bit. Scotch foam is used as filter material all the time.

 

Sushi.....yes, you could start wrapping the pods with some restrictive material to bring the airflow down, but again, it's going to be a trial-and-error type of project. Old athletic socks might be a good way to go.

And just remember the colortune plug is going to help you with the IDLE mixture (the pilot fuel circuit) adjustments, but really isn't useful for the main fuel circuit settings........which is where the differences in airflow become really significant.

 

True about the idle....

Yeah wrapping the pods is trial and error but at least the pods are easily accessible.

I just had this vision of a "block" of Scotch foam or something similar that you just cut out the shape of the pods and slip over them as one unit.

 

It's not just a matter of Re-Jetting the Carbs.
There is also some dynamic problems to overcome.

1. Turbulence.

With only Pods, the Intake Air Volume is Turbulent. The turbulent volume of Intake Air passes-over the Top of the Emulsion Tube and does not have an "Air Stream" compact enough to sufficiently reduce the Pressure and cause enough Fuel from the Main Jet to rise and be drawn into the Combustion Chamber.

Solutions:

Velocity Stacks, Modified Air Metering Ports on Emulsion Tubes; Larger Main AIR Jet.

2. Main AIR Feed

Obviously, there needs to be an Increase in the Main AIR Feed to allow a volume of air to surround the Emulsion Tube and be Metered through the Emulsion Tube Metering Ports to cause a sufficient Uptake bringing along Main Jet Fuel to enter the Intake Air Stream and provide a higher volume of Fuel to overcome the LEAN Condition with Pods.

This introduces several questions along with possible obstacles.

1. Since the Cubic Feet per Minute of Intake Air is NO LONGER regulated by a Maximum amount entering an Airbox Inlet. How do you apportion the Main Air Metering Ports on the Emulsion Tube?

2. What size Main AIR Jet will be sufficient to regulate the Air introduced at the Emulsion Tube?

3. Are we all standing on the ground and barking up the wrong tree?
Is the Main AIR Passage even large enough to supply the additionally needed Main AIR Volume needed to make things work?

 

Which is why the airboxes appear to us, the shade tree engineers, to have "too restrictive" of an air inlet leading to all sorts of hole drilling and the like. To keep the carbs (especially CV carbs) working properly at ALL RPM levels (and therefore all levels of intake vacuum) CFM has to be regulated which explains the design of the blasted airbox. More primitive carbs probably wouldn't care as much.

 

There's some Emgo pods that are foam and I've heard they allow less air in that the standard K&N type pods. But don't bother trying to restrict them. I really doubt it would work consistently across the 4 carbs. Just go for more fuel flow. Before you pay through the a!s for K&N pods, look around. There's some other brands just as good for a lot less. Sadly I only found out afterwards.
Anyway, I tried gluing together an airbox out of three pieces after getting them inside my XJ650's frame. Never really worked. The vibration always caused problems.
I think the key with pods is to go on every possible forum you can think of and badger people that have already pulled it off. And not just XJ forums. I did that for a few months and finally got a few guys to reply who had real world experience and success. It's worked great. We're all in this together, right? And hey, at least jets are pretty cheap.
Check out European and Aussie/NZ forums. A lot of people there go for the pods. In those places installing pods is not the federal offense many consider it here in North America. Good luck and keep us updated on your progress.