Author Topic: Carb questions regarding airbox removal on a CB 550 (Read 6245 times)

Way Way norcal · « **on:** February 03, 2013, 12:51:41 PM »

I understand this is a somewhat covered topic and I have read a few varying opinions. I spent the afternoon at a reputable local shop yesterday discussing removing the airbox on my CB 500. THe owner strongly advises against removing it. He said he had done it a few times and no matter what he did to the carbs he could not get them to run correctly. He said you will lose your start and stop low end performance. Good at top end but forget about driving the thing in traffic. My goal is removing he box, putting on a 4 to 1 header and aftermarket air cleaners and a possible re jet.
My reason for posting this new thread is, is it true? If so what can be done to get it to run right without the airbox. I am in the middle of a cafe build on this bike and I am at the point where do I or don't I pull the box off?
Any insight on this would be great.

TwoTired · « **Reply #1 on:** February 03, 2013, 01:56:22 PM »

It's true.

But, for those who prefer fashion to streetability, it doesn't matter.

Essentially, you are throwing away hundreds of man hours of induction work for a cheap "look" of popular pods.
Low and mid operation is not that important on the track. (Neither is engine longevity beyond end of race.)

If that's what you are going for, and have many hours of time on your hands for the rejet process, then go for it. Custom bikes should be just that and the operator should know all the intimate details of their bike's operation. Doing a correct rejet will get there. But, if you add parts that only work well around 9000 RPM, you'll be trading those gains for losses at low and mid range, particularly with a stock engine.

Reminds me of the old chevy race days, where people would put on bigger carbs for more HP in their SB for the drags. A 1000CFM carb from a big block motor did make some gains at WOT. But really, didn't make a significant boost unless you revved the motor to 9000 or higher (if it stayed together).
The street guys would try to mimic this for the drive-in show and tell, to turn heads, and it would give them a car that couldn't get out of it's own way around town, and they wouldn't dare make the engine go above 7000 RPM. It was a waste of time and money and they never really learned what their car needed, for what it was intended to do or actually asked to do.

Anywat, you can get it to run "well enough" to make the scene. But, many just don't know how well it will run on the street in stock form, and therefore live with the ills cafe conversions often encounter. Many are quite happy with this blissful ignorance. But, just why make a racer if you never intend to race it?

imo

goldarrow · « **Reply #2 on:** February 03, 2013, 03:48:05 PM »

+1 very well said.

My bike looks and runs great without pods

BobbyR · « **Reply #3 on:** February 03, 2013, 05:42:04 PM »

Your reputable shop owner knows what he is talking about. You can do things that can make the the bike better. Ignition, brakes and some suspension. This is time well spent.

RFogelsong · « **Reply #4 on:** February 03, 2013, 05:56:42 PM »

First off, listen to twotired, he's been at this for a while and as far as practical knowledge, you can't beat his advice.

Secondly, your post sounds like a stereotypical "cafe racer pods+4-in-1" post and there's a defined hive mind against that type of thing here unfortunately (each his own is my opinion) so I'm just warning you that this is kind of a popcorn type thread (along with oil threads)...so fair warning in case you didn't know, don't get discouraged if that's what you want to do.

Now, I understand why you posted, and yes, it's true. The reason it screws everything up has to do with the turbulence of the air flow coming into the throat of the carbs and the effects that has on carburetion. This is amplified at low throttle and has less of an effect at higher throttle openings, thus the effects you've heard of (bad There's a few streetability and good for racing). People out there that have modded pods to include some pieces of the stock airbox to try to smooth the flow, so you might try to search for some threads on that if you're still bent on using pods.

Also, you mention "possibly rejet" There's not gonna be a possibly about it. The good thing is that there's so many people who've been down this road that you might not have to do too much experimentation. As much as I like the open triangle look pods give you, I would advise against it for street use.

It's not gonna completely make the bike unridable, but you will have some stumbling until you get into the powerband for sure. Others have done it and you can too, but if you want the reliability and ridability that these bikes are known for, leave it on.

Christo · « **Reply #5 on:** February 04, 2013, 01:13:20 AM »

I recently purchased a CB550 and from day dot it wasn't running right. I was getting flat spots and it was running real rich. i played with the air screw to no avail.There was something not right with the carbs. Well thats what i thought. I was very fortunate enough to meet Dave500 and he looked at it in detail. He checked the timing, spark, etc, then the jets. It all looked ok. Next is the air filter he said. i was skeptical. Holding it up to the light it didn't look too great. Pretty clogged. I ran the bike without the filter to test the theory and OMG. I had a new bike. Couldn't believe the difference. I now have a makeshift filter awaiting the replacement. The bike now is running perfect. I would never even contemplate fooling around with the air box and filter now knowing how much of a difference it can make to its running performance.

Way Way norcal · « **Reply #6 on:** February 04, 2013, 09:03:34 AM »

Thanks everyone for the posts! Great info! It looks at this point like I am going to leave the airbox on and work around it.

70CB750 · « **Reply #7 on:** February 04, 2013, 09:18:24 AM »

Ride the crap out of it before you start wrenching. It helps to know what you have and defines what you want to do.

Way Way norcal · « **Reply #8 on:** February 04, 2013, 02:44:35 PM »

another quesiton...
I am considering a 4 to 1 exhaust swap. I know I will have to re-jet. How will this affect the carb performance if I leave all that on and stock minus the header and jets??

RFogelsong · « **Reply #9 on:** February 04, 2013, 04:13:43 PM »

I did just what you're thinking about on a 1975 cb550 (stock except 4-1 and jet to match). The carbs work fine with this setup (I had to change mains, air screw 1 turn out and I'm debating going one notch richer from stock on the needles but I haven't yet). I like it because it probably free'd up a horsepower or two and it definitely dropped some weight. Highly recommended, you shouldn't have any of the problems everyone was warning you about concerning pods

TwoTired · « **Reply #10 on:** February 04, 2013, 05:53:47 PM »

The 4 into 1 is supposed to work best at high RPM (if made for performance, ie not the MAC). It's a trade off for losses in efficiency at the low & midrange. Many brands of replacement exhaust (with a real muffler) seem to work well with stock jetting except the F model. Which seems odd since it came with a 4 into 1. But, the F muffler was a high pressure type which allowed leaner fuel settings in the carbs and that is exactly what Honda did.
If your 75 is an F model, you will have to rejet. But, it's pretty easy, as you just select the settings for the 4 into 4 K model.

Cheers,

BobbyR · « **Reply #11 on:** February 04, 2013, 07:23:32 PM »

I think you will find for all around performance, Honda pretty much figured out the breathing of it's stock motor. When people talk about getting an extra HP it is based on belief not fact. Valve adjustments, clean carbs, good ignition wires will go a long way toward optimizing performance.

If you like the look of 4-1 and the sound that has a psychological value which is OK, you should enjoy your bike. Smiles per mile is not a bad thing at all.

seanbarney41 · « **Reply #12 on:** February 04, 2013, 09:15:47 PM »

the 4-1 performance gain is from it being way lighter...stock sohc4 cylinder heads are generally pretty crappy and are not gonna benefit from exhaust system or air inlet mods

goldarrow · « **Reply #13 on:** February 04, 2013, 09:21:22 PM »

4-1 exhaust looks neat, and saves the weight, but stock 4-4 is the best! Both the look and sweet sound!

If your bike has good functional stock exhaust pipes, then keep it.

Why dont you post up some pics of your bike so we could help you better

Way Way norcal · « **Reply #14 on:** February 05, 2013, 09:46:43 AM »

Sure thing! Here is my bike
75 CB 550

And one of my 64 CT 200 I modified..

crazypj · « **Reply #15 on:** February 05, 2013, 09:53:13 AM »

It's possible, it's not easy, it's not something to do for looks.
It will take a long time to get carburation mediocre (even with multiple dyno runs and wideband EGA)
Unless you really like tinkering and prefer it to riding, don't screw around with stock airbox

Way Way norcal · « **Reply #16 on:** February 27, 2013, 08:18:48 AM »

anyone know what pipes my bike has on it? Pretty sure those are not stock.

geminimotors · « **Reply #17 on:** February 27, 2013, 09:43:15 AM »

They look like Jardine, possibly slipped on to stock head pipes.

freeze · « **Reply #18 on:** February 27, 2013, 09:51:41 AM »

I like the look of pod filters so I have spent an enormous amount of time fiddling with these carbs. The problem is: you can only adjust air/fuel mixtures at idle and wide open throttle...unless you have a lathe and are comfortable changing the taper of the needles and even after that it won't perform as well as the VERY restrictive factory air box. There will always be a hesitation when you roll on the throttle because the pressure inside the carb is too close to the atmospheric pressure outside the carb, hence the pods aren't restrictive enough.
Now the good part, there is a solution.
I took four empty yogurt containers that closely matched the size of my pods, cut the top lip and bottom from them and cut down the remaining portion (using about 1/3 of the side) and siliconed them inside the pod thereby reducing the pods inside surface area by about 1/3rd. This seams to replicate the poorly engineered airbox very well and uses stock jetting...only downfall is there will be no increase in performance, only appearance.

Way Way norcal · « **Reply #19 on:** February 27, 2013, 09:56:29 AM »

interesting!
How does my bike look overall? Any modifications on it from the photos?

Deltarider · « **Reply #20 on:** February 27, 2013, 10:08:17 AM »

Quote

This seams to replicate the poorly engineered airbox very well

Yeah, those pods are soooo sophisticated. A brilliant design.

freeze · « **Reply #21 on:** February 27, 2013, 10:19:15 AM »

Yeah, those pods are soooo sophisticated. A brilliant design.

[/quote]

I added that sentence just for you, and the other purests on here.

crazypj · « **Reply #22 on:** February 27, 2013, 11:06:30 AM »

Cheap pods are just a waste of money and are more restrictive than stock airbox at high rpm
K&N will work well if you spend enough time messing with carbs
I have no idea of the total time I spent on my 550 to get it working right as it was done over a 2~2-1/2yr period (I would ride it until I couldn't deal with the problems any longer then do some more mods)
Eventually it was pretty good, 41mpg, 127mph (previously 23~26mpg, 112mph)
82mph in second gear @13,500rpm.

alacrity · « **Reply #23 on:** February 27, 2013, 11:30:10 AM »

wow crazyPJ - those are serious numbers for a 550.
How about you just post EXACTLY what you are running and at what setting and we can use that as baseline to copy. After all, you've made the investment, why not recoup some of that in goodwill?

:-)

Bru-tom · « **Reply #24 on:** February 27, 2013, 11:32:08 AM »

^^^ agreed

Way Way norcal · « **Reply #25 on:** February 27, 2013, 11:53:49 AM »

I'd like to see that as well. Numbers like that I would like to do what you did!!!

flybox1 · « **Reply #26 on:** February 27, 2013, 12:03:14 PM »

your pipes definitely look like Jardines.
I had similar ones on my 350F. their mfr stamp woud be on the rear mount bracket.
i always dig the 35+ year of sun-fade paint jobs on these brown bikes

freeze · « **Reply #27 on:** February 27, 2013, 04:57:26 PM »

"Cheap pods are just a waste of money and are more restrictive than stock airbox at high rpm"

Only half this statement is correct and that is cheap pods are a waste of money...
I have tried every manufacture of pods both expensive and cheap and NONE have been more restrictive than the stock airbox...
And this restiction (stock airbox) is how a simple, basic, non accelorater pump type carb works on these bikes.
Lets not forget, Honda was building an inexpensive, reliable, dependable motorcycle for the masses. and INMO did a pretty damn good job.
BTW, I too perfer K&N.

BobbyR · « **Reply #28 on:** February 27, 2013, 05:07:50 PM »

Do people have success with pods, sure they do. If you take the time to tweak everything you may be successful. Some report that side winds cause some power loss probably due to dirty air killing the vacuum. Honda went to the trouble of actually putting the air intake pointing backward where the air was quieter.

As far a cost I am sure that injection molded plastic box cost a lot more to make and mount than sheet metal funnels with some foam rubber over them.

crazypj · « **Reply #29 on:** February 27, 2013, 05:12:56 PM »

Quote from: freeze on February 27, 2013, 04:57:26 PM

"Cheap pods are just a waste of money and are more restrictive than stock airbox at high rpm"

Only half this statement is correct and that is cheap pods are a waste of money...
I have tried every manufacture of pods both expensive and cheap and NONE have been more restrictive than the stock airbox...
And this restiction (stock airbox) is how a simple, basic, non accelorater pump type carb works on these bikes.
Lets not forget, Honda was building an inexpensive, reliable, dependable motorcycle for the masses. and INMO did a pretty damn good job.
BTW, I too perfer K&N.

I've never seen a stock air filter collapse but I have seen cheap pods collapse, if you didn't put them on a flow bench, it's just an opinion. (and before you ask, yes I have but no longer have access to data)
Accelerator pump has nothing to do with air box design, SOHC CB750 used accelerator pump in 1977 due to emissions not re-designed air intake
As for air intake pointing backwards, it was the technology of the day, all modern sport bikes use 'ram air' forward facing intakes

Way Way norcal · « **Reply #30 on:** March 28, 2013, 02:20:35 PM »

anyone spot anything else on this bike of mine of any particular interest??

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Author Topic: Carb questions regarding airbox removal on a CB 550 (Read 6245 times)