Author Topic: What carbs do I have? Twotired I know you have the answer.  (Read 2917 times)

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Offline cbass*gxc

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What carbs do I have? Twotired I know you have the answer.
« on: February 27, 2008, 07:26:46 AM »
It says they are Keihin PD carbs (78 cb550) in the carb faqs but when I look I cant find anything on them.  I am needing to get new jets and do not know where to buy them.  I have been reading all the info about these carbs and I must say Twotired you know all kinds of good #$%*.  Anyways I should be getting my motor back together in the next few days and was told I would probably need to change the jet size because I have shortened the exhaust by about 12" and am putting pods on it.  I would like to find out which sizes I may need so I can get them ordered before I need them.


Thanks in advance,
Jay

PS Here is a pic of the carbs.
« Last Edit: February 27, 2008, 07:30:44 AM by cbass*gxc »

Offline KB02

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Re: What carbs do I have? Twotired I know you have the answer.
« Reply #1 on: February 27, 2008, 07:44:46 AM »
Well, I'm not TwoTired, but you've got screw on bowls, and the set up for an accelorator pump. Other than that... well, I can't tell much beyond that. I would say late 70's (77 or 78). Any number castings or markings on the carb bodies?
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Offline cbass*gxc

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Re: What carbs do I have? Twotired I know you have the answer.
« Reply #2 on: February 27, 2008, 07:50:43 AM »
Ya they are off my 78 cb550, I just cant find any info on them.  And after reading about them in the faqs it seems to me that Twotired knows his #$%* and may be able to help me out.

Offline bryanj

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Re: What carbs do I have? Twotired I know you have the answer.
« Reply #3 on: February 27, 2008, 08:22:01 AM »
Why would you need jets? They rarely,if ever wear.
The 77/78 carbs have little info even in the genuine Honda shop manual.
Mains are simple screw in same as 750 but pilots are push fit---LOADS of posts on those and yes they do block up for a pastime.
Gasket sets are same as 750A
As they were only used for the last 2 years of an 8 year production there is little back up for these
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Offline bender01

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Re: What carbs do I have? Twotired I know you have the answer.
« Reply #4 on: February 27, 2008, 08:28:05 AM »
not sure but are those floats on upside down?
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Offline cbass*gxc

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Re: What carbs do I have? Twotired I know you have the answer.
« Reply #5 on: February 27, 2008, 08:35:37 AM »
I have been reading and seen that if you put pods on you need to put new jets in.  At least that is what I thought I read.  So if I do need to replace some jets which ones would I need to replace? 

Bender -  I hope they are not upside down.  That was before disassembled them and that was how I put them back together.

Offline edbikerii

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Re: What carbs do I have? Twotired I know you have the answer.
« Reply #6 on: February 27, 2008, 08:38:47 AM »
Search for pods, jetting, cb550.

Or just go here:

http://forums.sohc4.net/index.php?topic=22036.msg258435#msg258435
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Jetting: http://forums.sohc4.net/index.php?topic=20869.msg258435#msg258435
Needles:  http://forums.sohc4.net/index.php?topic=20869.msg253711#msg253711

Offline cbass*gxc

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Re: What carbs do I have? Twotired I know you have the answer.
« Reply #7 on: February 27, 2008, 08:55:57 AM »
Search for pods, jetting, cb550.


So the only thing that wasnt stock was your mains?  Where do you adjust your needle at?  Sorry this stuff confuses the #$%* out of me.  So in my pic above the screw in jet is the main and the little one is the slow jet?

After looking at that pic you really cant see the little one.  But the main is the jet you can see?

I just read TT's post in that topic and I see what I need to do.  He says the best way is to up the jet size by 005 to 010.  Raise the throttle valve needles and turn in the air screw a bit. 

Now I just need to figure out where I can get the jets.
« Last Edit: February 27, 2008, 09:09:26 AM by cbass*gxc »

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Re: What carbs do I have? Twotired I know you have the answer.
« Reply #8 on: February 27, 2008, 09:23:00 AM »
good luck Jay, there's some where you can get jets, too many guys have the 550's for there not to be any available, just keep lookin. Your floats look like their on the right way too. ;D And the carbs. confuse the crap out of all of us at one time or another, I learned how to work on carbs. when I was 14 and I'm 30 now and they still get me every once and a while ;D
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Offline cbass*gxc

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Re: What carbs do I have? Twotired I know you have the answer.
« Reply #9 on: February 27, 2008, 09:26:56 AM »
good luck Jay, there's some where you can get jets, too many guys have the 550's for there not to be any available, just keep lookin. Your floats look like their on the right way too. ;D And the carbs. confuse the crap out of all of us at one time or another, I learned how to work on carbs. when I was 14 and I'm 30 now and they still get me every once and a while ;D

lol  I am hoping that once I get it back together I can use the factory jets and tune it to be close.  I am not wanting this bike to race or to see how fast I can go, more as an around town bike.  I was thinking the same thing about the jets, there are too many of these bikes to not find them.  I will post up my results when I am done.

Offline Cvillechopper

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Re: What carbs do I have? Twotired I know you have the answer.
« Reply #10 on: February 27, 2008, 09:27:12 AM »
You should be able to get those mains from just about any of the parts stores listed in the FAQ section.  I think the screw-in type Keihin mains for the later years are all the same.  
http://www.crc2onlinecatalog.com/Index_Main_Frame.htm
Look under "Fuel System parts", "Misc Carb Parts" just less than 1/2 way down.
Just order the size(s) you want and screw them in.

« Last Edit: February 27, 2008, 09:28:43 AM by Cvillechopper »
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Offline TwoTired

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Re: What carbs do I have? Twotired I know you have the answer.
« Reply #11 on: February 27, 2008, 09:37:26 AM »
On the side of your carbs, just below the raised PD letters, you will find a small flat surface with your exact set up numbers stamped into the carb body.
The PD carbs were only used on the 77-78 K3 models and do NOT have an accelerator pump.

Since you are going use pod filters and a lower restriction exhaust, which likely has different flow characteristics than the stock units, and your particular combination will have different flow characteristics than anybody else's filter/pipe combination, you will have to determine which slow jet, slide needle, and main jet size works best for your individual set up.

Your floats are correctly installed

The exhaust restriction reduction changes the mixture requirements due to more complete cylinder evacuation of un-combustible gases.  Meaning you will likely need to open the jet orifice to provide more fuel for the larger amount of oxygen now entering the cylinders.  As back pressure can be modal, (different at different RPM settings) each of the carbs fuel metering adjustments can be effected in different mounts.  Expect an IMS (Idle Mixture Screw) change from stock settings, at least (mostly impacting the throttle pickup from idle), and probably main jet orifice, and even Slide needle valve clip position adjustments.

The air filter change will also have its own impact on carb settings.  Pod filters have (usually) less filter media restriction.  And, since the engine is sucking through this media, the depth of the vacuum is reduced in the carb throat.  This reduction pulls less fuel from any given fuel jet orifice.  Although the volume of air the engine uses hasn't changed, (assuming valve timing or engine displacement remains the same) the pressure drop in the carb throats does.  So, in order to restore the proper fuel-air mixture, the fuel metering orifice size may need to be increased for the filter restriction change.  As the adjustment range of the IMS is limited, you may need to increase the size of the slow jet, (the smaller stub next to the center big main post in the carb bowl) to restore good throttle response from idle.  Also, the main jet size may need to be addressed for wide open throttle (WOT).  Then, for the the 1/4 to 3/4 throttle positions, the slide needle clips may need changing to improve mid-range mixture.
I'll post a chart showing adjustment significance related to throttle position.

Jet size prediction:
Beats me.  If I knew quantitatively how the restrictive characteristics changed from the stock components, I might venture a guess.  But, such data doesn't exist, or has been unavailable to me.  For the home mechanic, reading spark plugs after a plug chop is the most economical route. Usually several runs and jet size/needle adjust changes will be done during the process.   A Dyno is faster, and more expensive.  But, will yield a better running bike.

Cheers,

Edited for typos

« Last Edit: February 27, 2008, 10:21:03 AM by TwoTired »
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Offline Johnie

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Re: What carbs do I have? Twotired I know you have the answer.
« Reply #12 on: February 27, 2008, 09:40:46 AM »
Man Two-Tired...you are a walking and talking service manual.  Simply amazing...I hope your wife appreciates you like we do on this board...  ;D
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Offline cbass*gxc

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Re: What carbs do I have? Twotired I know you have the answer.
« Reply #13 on: February 27, 2008, 09:45:23 AM »
Thats what I am saying.  This guy is a walking motorcycle encyclopedia.  Thats why I put that in the title.  Anyways I read what you put TT and think I may have to read it a few more times to get it.  I am going to try and get the engine and bike back together this weekend and I will post after I do.

Offline greenjeans

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Re: What carbs do I have? Twotired I know you have the answer.
« Reply #14 on: February 27, 2008, 11:52:54 AM »
I've already read it twice.....good thing he's on our side.
Yep, I'm the kid that figured out how to put things back together...eventually.

Offline edbikerii

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Re: What carbs do I have? Twotired I know you have the answer.
« Reply #15 on: February 27, 2008, 05:10:26 PM »
Of course, everything TT says is absolutely true.  You will have to find out for yourself what works best for your bike unless you have an identical setup to somebody else's.

It is my belief, however, that the big bottleneck on my 77 CB550 was the airbox.  The Mac 4-1 that I have is not known to be the most free-flowing exhaust, but changing out the exhaust made very little difference in performance until I replaced the airbox with the pods.

Whatever you do, don't forget the routine:

1.  dial in the main jets as needed at WOT throughout the RPM range.
2.  dial in the needles as needed for 1/4 - 3/4 throttle openings throughout the RPM range.
3.  dial in the air jets and/or pilots for idle and just off-idle.

Once I had the mains in order, I then proceeded to mess with the needles, but both times (up and down), I ended up returning to the stock needle position.

Idle was too lean to begin with, even with stock airbox and exhaust.  However, you probably won't need to worry about the slow jets.  Just richen up the screws.

So, in short, my suggestion to you is to go to the local shop, buy some 105 mains (keihin screw-in).  The shop will probably have tons of them pulled from the old 750s.  Install your pods and oil them properly.  Undo the float bowls with the carbs in place, unscrew the stock main jets, and screw in the 105 jets.

That should be a good starting point.  If you find that to be just right, then you're golden.  If not, then at least you'll be closer, and you'll know the difference between stock jetting and 105s.

Plus, you've only spent maybe an hour installing the 105s your first time.

Good luck
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Jetting: http://forums.sohc4.net/index.php?topic=20869.msg258435#msg258435
Needles:  http://forums.sohc4.net/index.php?topic=20869.msg253711#msg253711

Offline cbass*gxc

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Re: What carbs do I have? Twotired I know you have the answer.
« Reply #16 on: February 27, 2008, 05:33:17 PM »
Thanks ed.  So will the bike run with the factory settings, just not as good? 

As far as getting the jets, the 750 jets will fit in my carbs?  I will have to call around tomorrow and see if I can find some.

« Last Edit: February 27, 2008, 05:38:23 PM by cbass*gxc »

Offline CBJoe

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Re: What carbs do I have? Twotired I know you have the answer.
« Reply #17 on: February 27, 2008, 05:36:48 PM »
I've already read it twice.....good thing he's on our side.

I like an individual who compares a motorcycle mechanic to a strategist   ;D

Makes me feel like i'm goin' to war when I put on my greasy jeans and pick up my impact tool  ;D
 
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Offline cbass*gxc

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Re: What carbs do I have? Twotired I know you have the answer.
« Reply #18 on: February 27, 2008, 05:40:09 PM »
Holy crap.  I did not even see the carbs in the back of the manual!  CB550K1 Supplement.  I was looking at the 500 and trying to figure out from those.  Told you this stuff confuses me.

edit - So should I sync the carbs before I mess with the jets or after or both?
« Last Edit: February 27, 2008, 05:47:55 PM by cbass*gxc »

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Re: What carbs do I have? Twotired I know you have the answer.
« Reply #19 on: February 27, 2008, 06:17:45 PM »
It never hurts to sinc your carbs, as long as you do it right, but there are tons of how to's on that and it isn't that hard.

Just a quick question.  Why did you go to pods?  (Sorry I may have missed this)  I asked because if you say that you want to use the bike for around town then pods are not the best option.  From what i have read they only give you more in the top 3,000 RPMs.  So why not just stay with the stalk air filter and box?

Offline cbass*gxc

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Re: What carbs do I have? Twotired I know you have the answer.
« Reply #20 on: February 27, 2008, 07:05:00 PM »
Well to be honest I like the way the bikes look with pods, but I am going to make the frame a hardtail so I will not have room for the airbox.  Plus at the moment my bike is lowered 4 or 5 inches as it is, so I am not sure if it would still fit.


Offline JZEROE

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Re: What carbs do I have? Twotired I know you have the answer.
« Reply #22 on: February 27, 2008, 11:34:22 PM »
I have a 550, though an older one with different carbs (push-in jets). They were a total pain to find, but Speedmotoco hooked me up. I know I probably sound like an ad for those guys, but seriously, they always have what I want, and send it out quick. Plus, they're knowledgeable.
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Offline cbass*gxc

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Re: What carbs do I have? Twotired I know you have the answer.
« Reply #23 on: February 28, 2008, 07:05:30 AM »
Thank JZ, I will check them out.