Topic: '77 CB550F jetting for pods and stock 4 into 1?

[geoluv]

I have a '77 CB550 F2 Super Sport.  It has it's stock 4 into 1 exhaust, very beautiful I must say.  It came to me without an airbox so I slapped some paper/mesh pods on.  I believe stock jetting is 38 mains and 98 secondary, a little leaned out compared to the jetting of the other years.  Anyway what jetting should I do for the pods and stock 4into1?  I'm thinking either 105 or 110 mains and leave everything else the same? 

Let me know your thoughts. 

[flatlander]

98 mains and 38 slow is stock.

the "bottleneck" of the system on the stock 550F is the 4-1 exhaust. the pods won't give you any inprovement with your setup. for good drivability and easy tuning i recommend you keep searching for an airbox.

or there was a single K&N filter made that's mounted to the stock plenum, replacing the filter box. it is discontinued but occasionally still pops up...

[Stev-o]

I also have a 550F with stock exhaust and love it.   Personally, I would get an airbox and ditch the pods since it sounds like your bike is mostly stock.

All the cafe guys remove the airbox, so they can be found and are reasonably priced.

Got pics of your bike?

[TwoTired]

The pods don't do anything for air volume below about 9000 RPM.  What the pods do is change the carb throat air pressure, which effects the driving force of fuel through the carb jets.  The differential pressure is lowered with pods, therefore less fuel volume flows.  The engine still gulps the same amount of air as with the stock air filter system.  So, the effect is the mixtures with a pod change become more lean, pretty much throughout the operating range.
The idle mixture can be improved with the air screws.  The midrange with need the slide needles raised, guessing one notch, and the main should probably go to 100s.

It will be a trial and error adjustment unless you have a Dynamometer or a test track to do do successive and repetitive plug reads while under full load in each operating throttle range.
Be warned, your final result of much effort will be a jetting compromise for the specific characteristics of the pod examples you have.  No manufacturer guarantees the flow, pressure characteristics between example offered and certainly not among manufacturer offerings.  Further, the engine will be an MPG hog compared to the stock set up.

All my operating Fs still have the stock air box system, as I believe it is foolish to replace the very well engineered stock system with the cheapest off the shelf compromise available.  And you will have far less issues with crosswinds and leg position affecting the air/fuel mixtures.  And then there is washing and rain water fouling to consider which can damage the paper.

Best of luck.  I think the 550 F models are best of breed.

Cheers,

[jlh3rd]

I also have a 550 f, unrestored and all original. The bike runs beautifully ( and looks it) and the engine, carbs etc, have never been messed with....which is my point. The stock configuration works the best, in my opinion. I agree with the others, get a stock air box..you say it’s a beautiful bike, why not let it run the way it should.

[geoluv]

i got the bike for $430, the bike as a whole it's definitely not a looker (I was referring to the exhaust alone as beautiful.)  it has 24,000 miles on it.  although the airbox pieces are available they are hard to find as a complete set with all the unique spacers and bolts and boots and all the pieces can add up to $100 or more pretty quickly.  New jets are $2 each.  The pods were free because I already had them. 

Ill definitely be on the look out for a complete air box set up but in the mean time i would like to throw the best jets for pods on my 4into1.com order for the time being. 

All these points being made about fuel economy and ease of tuning I am already aware of.  Just looking for someone who has jetted for pods already on the '77 550 F model with stock 4 into 1 exhaust to give some input. 

[Bankerdanny]

I would follow what Lloyd (TwoTired) said then, 100 mains with the needles one slot lower than stock.

[Stev-o]

$2 jets have caused tuning problems for many.

Stick to genuine Keihin ...

[TwoTired]

I see you wish to pursue the cheap route.  Be aware that cheap is not only an economy indicator, but also a quality indicator.  I suggest that if you really wish the bike to run well you abandon the cheapest outlay goal, and pursue that which will make your bike run well and be enjoyable.  However, if constant maintenance attention is what you enjoy, do continue with trying to make cheap pods "work".  You'll learn a lot if you are successful in the endeavor.

Because you got the bike cheap does not mean it will be cheap to make it run well.  That may be the very reason it was sold to you cheap.  No matter, the value of the bike is not in the purchase price.  It is in the enjoyment of it. The bike in my avatar was $100 when I purchased it. It took another $500 to make it a well steetable, reliable bike.  It was money well spent, imo.  I have another F that I rescued from the junk yard for $300.  It took another $1200 to make that bike another well streetable, reliable bike.  This was over 20 years ago and they still are great bikes to enjoy.  Would I sell them for less than insurance replacement value of $300?  No way.  They are worth far more to me.  A dealer would want $3000 for each one.

Imagine getting a Ferrari for $100, and then refusing to spend more that $100 on needed tires because that would be more than the car was worth (in purchase price) when, in fact a well operable Ferrari, is worth many thousands more.

I doubt you'll find first hand credible reports of pods with the stock exhaust.  The imagination of bike appearance modifiers seldom include keeping the stock exhaust.

Finally, the bike runs well with stock parts.  Aftermarket items do not have proven replacement value or manufacturing specs.  They are sold solely for profit reasons, and leave the functional operation issues for the buyer.  I mean would you bother to claim a refund on a $2 part, as well as prove the part offered was indeed defective?  There are parts that "work" and then there are parts that "work well".  How will you decide which you have chosen?  How much is lack of frustration worth to you?

Cheers,

[scottly]

The pods don't do anything for air volume below about 9000 RPM.  What the pods do is change the carb throat air pressure, which effects the driving force of fuel through the carb jets.  The differential pressure is lowered with pods, therefore less fuel volume flows.  The engine still gulps the same amount of air as with the stock air filter system.  So, the effect is the mixtures with a pod change become more lean, pretty much throughout the operating range.

If the differential pressure is lowered, it means the pods have less resistance to airflow, allowing greater airflow, and larger jets to provide the same amount of fuel.
Also, not all "pods" are the same: pleated paper pods are more restrictive than pleated wire/gauze K&N type pods. The exhaust is not as major of a tuning factor as the intake side. The general rule of thumb is to increase the main jets by two sizes for free-flowing pods.   

[TwoTired]

If the differential pressure is lowered, it means the pods have less resistance to airflow, allowing greater airflow, and larger jets to provide the same amount of fuel.

I disagree.  From aerodynamics, duct, and fluid flow studies, pods shorten the airway duct path and presents atmosphere pressure closer to the carb throat.  The shorter the duct, the faster atmospheric pressure can present to the exit points of the fuel jets.  This creates less differential across the jet orifice for less fuel flow volume, for the very same air flow volume as before. This happens whether the pods are at the carb mouth or if the carb mouth was open to atmosphere.

There is no way pods can present more air than the engine can demand, airflow volume is unchanged for a stock motor given a simple change from stock set up to pods.   At very high flow rates, one type of filter membrane can allow  more flow volume than others, as the membrane must create turbulence, being an obstruction to airflow.  The stock system allows that turbulence to return to laminar flow before presentation to the fuel jet orifice exits.  Pods do not.  The turbulence can be modal in that it can linger a farther distance as air flow volume increases, or even subside again at certain air flow speeds.  The issue here is when these "fingers" of turbulence reach into the fuel jet exit points, effecting the differential pressure and fuel volume non-linearly with engine RPM, creating lean points in the throttle curve.

Also, not all "pods" are the same: ...

I agree with that, for sure.  Further, there isn't much assurance that pods will work the same from example to example, even within a manufacturers offerings.  You know of some that have a quality control or test program?  Any that offer performance curves/data?

Cheers,

[Gurp]

I wont bash your choice duder.
Stick with genuine jets or at least higher quality ones. I had 2 buck jet issues before. It's far more of a headache than a few bucks is work. As far as jetting goes
Two tired is right on the 100 mains. Don't forget the pilot as well. I think stock on that bike os a 38. Go up a size or 2 there too.
PS i have a complete airbox with little screwes off a 74 550 id sell cheap if youd be interested.