Topic: Jetting the CB550 PD series carbs....

[Scott S]

 I know that jetting ANY carb beyond stock/factory settings is a trial and error basis. Add in factors such as a larger cam, ported head, aftermarket exhaust, etc., and it's (possibly) a long road for anyone.

 I have a '78 CB550K with the PD46C carbs.
 I plan on the following mods:
-CB650 cam
-mild P&P'd head, per the Hondaman stuff on this site
-Jardine 4-1 header
-Pamco ignition
-possibly an oil cooler, if it clears the exhaust

 For those of you with the '77-78 bikes that have had to rejet, can you list your mods and where you ended up on the jetting?

 Also, did you have to raise (or lower) the needle? Did you change just the main or the slow jet, too? How many turns out on the idle mixture screw?

 This will at least give me a good starting point, and an idea what jets to order for my "trial and error" tuning.

[Scott S]

 Also, what's your favorite place for getting jets? I did a search and most of the threads are from'05-'07. Where are you guys currently going for jets?

 Ever use http://www.siriusconinc.com/index.php ? They have some pretty good prices on jets, gaskets, etc. I think I'll call them tomorrow and see if they can make me a "jet kit" like they have listed for some other models.

 For example: They list this kit for the CB360. It has screw in jets for Keihin carbs. They look exactly like the CB550 jets in the picture and the sizes are pretty close to what I need (maybe a 100 instead of that 120). Would these work in my PD carbs?

http://www.siriusconinc.com/pro-detail.php?pid=&product_id=3829

[luap]

sirius is the stop for jets id go with the jet kit 16 jets for 45.00 an they will substitute other jets for you past couple bike stock motors pk22 an pk3 pods mac 4into1  open home buit baffle 110;s stock idle needle 4 to 5th needle clip  new build i just did stock 78 4into1 110;s 40 idle 3 possion on clip its petty poppy though need to make a baffle see if that helps out a bit im in az though so everyone is different

[Elniniomuchachos]

I'm in Arizona as well with a stock engine, stock 77 4-4 exhaust pipes, EMGO Pod filters. Right now I have in 97.5's for the main jet. I didn't mess with the slow. Needle jet is set at the highest mark. And Idle screw is set to two turns out. Bike runs pretty well, though I would like to get it running better. Top speed went from 100 down to 90 when winter hit. So I probably need to up the mains one more.

I know how you feel when it comes to jetting. I was sort of paranoid, but it worked itself out. In fact I first started with 115's  which was so rich the bike spat black smoke out. Just take your time.

Oh, and a tip for getting the bowls off quickly - use a 6.5mm socket with a Philips screw driver bit and it's much easier.(Because of clearance issues with a regular screw driver.) AND DON"T OVER TIGHTEN THOSE SCREWS! I over tightened two of them and they striped.

Luap- You may want to consider using some periods...

[Dimitri13]

I've bought all my jets recently from jetsrus.com

[Scott S]

 I picked up some jets from a guy over on DoTheTon.com. He had jetted his bike and had these left over. I got some 90, 95, 112.5 and 115's for stupid cheap. I feel like I should have some 100 and 110's on hand though.....don't you think?

 I also have some 42 slow jets, but it seems like most people don't mess with those.

 Sounds like raising the needle is pretty common, too. These carbs are pretty lean from the factory...

[Scott S]

 Also, the float bowl gasket isn't listed as a separate part #. It also looks similar to some other models....was it used other places, too?
 I find that you can sometimes get better search results and even prices when you look for a part that was also used on a "less desirable" model than our beloved SOHC's. 

[Kong]

I set up the 550 PDcs for the bike I was building (and will again soon) like this.  105s and the needle up 1 notch.  This is with a stock 550 except for the 650 cam.

[Scott S]

 "..needle up one notch".... Meaning you lowered the clip to raise the needle? To make it richer?

[Kong]

Yep.

[Scott S]

 Bumping this one back up.
 I'll be at this point soon and want to gather more info. Here's some more detailed specs on my engine, too:

CB650 cam

1.39 exh.       lobe               1.40 in.
1.110            base circle       1.110
0.280             lift                0.293


 I'm gaining some lift (.021 on the intake and .028 on the exhaust). With 1.1:1 rocker arm ratio, the CB650 cam has .322 intake and .308 exhaust lift at the cam.
 It also has about 8 degrees more duration than the stock 550 cam, so that would be approx. 248* int. and 253* exh.
 This cam is similar to "hot street" cams that were sold my Yoshi, Action Four, etc. back in the day.
 
Engine has been bored out 1.00mm, which will increase displacement from 544cc to 563cc, about a 3.5% increase.
 
 Head has been ported and polished, match ported manifolds, etc.
 
 Exhaust is a vintage, new old stock Jardine 4-into-1 with equal length runners of approx. 27", a 10" collector and a 19" muffler/baffle. Overall length, when assembled, of approx. ~54-55".
 
 In addition to the stock jets, I have:
90, 95, 100, 105, 110, 112.5, 115 and 120 mains.

[Scott S]

 I'm thinking, with my mods, try raising the needles one clip and the 110 mains.

 What about float level? The '77 carbs were set at 14.5mm. I've heard of raising the float level to help "richen it up" a little when it's on the mains. Or, just stay with the stock 12.5 mm setting?

[bwaller]

The stock PD mains were 90? It doesn't hurt to start a tad rich and I think you might be afterall on both the needle & mainjet. Leave the fuel level in stock territory.

[cwchan]

are you going to run the stock airbox or go with pods?

[Scott S]

 Stock airbox with a Uni-Filter.

[dawdish]

Here is a formula I found on another site, I like getting my jets from DCC.


Quote
MAIN FUEL JET SIZE CHANGES NEEDED PER TYPICAL MODIFICATION:

Note:
This document is based on Mikuni Carburetors. But the theory follows through on all carburetors. Be aware that Mikuni Main jets increment in steps of 2.5, Hitachi Main jets increment in steps of 2.0. Hitachi Main jets (screw in style [Yamaha XJ's] are available in sizes from 110-134 in increments of 2.0. All this means that if you find you need to go up 4 steps on the main jets according to this chart (2.5x4) the step up would be 10.0. For Hitachi mains the step up would be 5 jet sizes (2.0x5) since following this chart for Hitachi mains would put you at 8.0 which is very close to 7.5 which would be 3 steps according to this chart. 
Jetting Recommendations
by Denny Zander
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.

[Scott S]

 Dug into these today.


 All the float heights were different and all of them were set very high....meaning the measurements were high, keeping the fuel level(s) low in the bowl.
 After searching and searching and searching about the proper float height, I got a headache and decided to go with 13 mm all across the board. When I set them at 14.5 mm, the slow jet wouldn't have even been in the fuel  level, to my untrained eye.
 Here's how I measured it:


 And here's how they look at 13mm.



 Now.....About the needles. It appears to me that in order to change the needle clip, I have to disassemble the whole rack of carbs. I really, really don't want to get into that..
 Am I overlooking something? Is there a way to remove the slide and gain access to the needles without de-racking the carbs?

[lucky]

No you do not have to take apart the carbs.

That bottom photo of the float looks like it is off.

You need some help.

[seanbarney41]

set your floats with the clear tube method...you want your fuel level in the bowl to be about 3 or 4 mm below the gasket

[Rhummy]

I found this place on a search for cb550f jets:

http://www.power-barn.com/servlet/StoreFront

$2.25 each for the Keihin jets.  No kits, but hey, take what ya can get lol

[Scott S]

No you do not have to take apart the carbs.

That bottom photo of the float looks like it is off.

You need some help.

 Care to elaborate?

 The bottom pics is of the same carb, same float height/setting as the pic above it. Measuring from the gasket surface to the tip of the float (non pivot end) I have them set at 13mm. Problem? If so, why?

 Can you explain to me how to get the slides out w/o disassembling the carbs? I've done it on the earlier CB500/550 carbs, but I just don't see how to do it on the PD series w/o taking the carbs off the rack and separating them, which entails taking the choke butterflies, etc. all apart.

 Rhummy, I have plenty of jets. I used 105 mains since I've done some head work, CB650 cam, 4-1 exhaust ad UNI filter in the stock airbox.

[Scott S]

 BTW, my procedure for checking float height is to tilt the carbs until the floats hang freely, then tilt them back until the floats just touch the needle valve. Touching, but no real pressure or weight on them. The carb bank is slightly tilted at this point.

 I measure at the tip of the float, non-pivot end, and set them at 13mm. This is at the end with the IMS screw.

[lucky]

You cannot just arbitrarily decide what the float level should be. Cheeeesssshhhh!!!

There is a specification and you need to find out what that is.
I would bet it may be the same as the CB750. That is why you need a workshop manual so you can get the correct information.


To remove the slides is another reason to have a work shop manual so you can read how it is done.

Do you notice how all the responders on this forum are giving you different information and telling you different measurements and they do not say where they are measuring from or to, etc.,.  Crazy.
There is a page in the workshop manual and it tells you the measurement. They should be able to give you the page number. There is no dispute.

Ok...I looked it up online but I would still rather have a workshop manual.

1978 CB550K
Float level 12.5mm

So with the carb upside down measure from the top of the float to the edge of the cab body.

Do not worry about the weight of the plastic float on the float valve. It is so light it will not push down the float pin. you would have to push it down with your fingers. With the old bras floats it was a concen but not with these lightweight plastic floats.

12.5mm is .492 thousandths.

That is so close to 1/2 inch lets just call it 1/2 inch. Because if you take a pair of calipers and look at that .006 thousandths difference it is NOTHING.

The float level will NOT effect HOW the engine runs UNLESS
 it is so low on fuel it runs out of gas OR it has so much gas in the bowl it starts flooding all over.

I am not angry and I am trying to help you.

Measure with the carbs upside down.
Measure from the top of the float down to the carb body where the o ring sits.
1/2 inch.

Thats it you are done.

[Scott S]

 If you'll calm down and read my replies, you'll see that I searched extensively. I read MULTIPLE settings for the '77-78 550K PD series carbs.

 I have a factory Honda manual. I printed out DOZENS of pages of supplements for the '77-78 K models.

 This thread mentions setting it farthest from the pivot:
http://forums.sohc4.net/index.php?topic=93668.0

 This:
 The Clymer is ignorant of the PD carbs found on the 77-78 Cb550K.

Below is a copy of a couple pages in the little Honda Carb specs booklet provided by Honda.

According to Honda, the 78 CB550K with the PD46 carbs should have a float height of 12.5mm.

However, when I did the carbs on my 78 550K.  They were all set at 14.5mm.  Since it ran well with this setting at one time, I left it at 14.5mm and it does run well at that setting.  So, I don't think the setting is all that critical on the stock machine.

I feel I must warn you, though, that the PD carbs were pretty finely tuned to the stock air filter and exhaust.  Don't use the 12.5mm setting unless the intake and exhaust are still being used on the bike.  In fact, this bike needs to be rejetted, just by changing to a more open exhaust or the engine will run lean and hot.  If the stock air filter is also changed from stock, even more drastic and thorough jetting changes are required.
I dread the day when my stock 4 into 4 rusts out, as stock replacements are rare and costly, these days.



 ...is from this thread on the PD series carbs, which mentions the discrepancies on the '77-78 models:
http://forums.sohc4.net/index.php?topic=80077.0

 This thread: http://forums.sohc4.net/index.php?topic=67667.0

 ...touches yet again on how to measure them and the float settings for the '77-78 PD series carbs.
 
 I am running a CB550 with a 1.00 mm overbore, ported and polished head, 4-1 Jardine and UNI filter in the stock air box.

 Now, if you'd care to offer some constructive criticism or helpful advice, I'm all ears.
 Better yet, show me a link to some factory instructions on changing the needle height without de-racking the carbs. Or, maybe a nice explanation for someone who's willing to learn.
 While we're at it, let's discuss float height settings and where/how to measure. If I'm doing it wrong, gently explain to me how and why and educate me as how to do it.

 Thanks in advance.

[TwoTired]

Float height book settings only apply to float needles that have the stock spring pin pressures.  (And, the springs must not be compressed during the measurement.)
If you use non-stock float needles, the clear tube method is the only way to get correct fuel levels.

If you lower the fuel level in the carb bowls, it effectively leans the mixtures for all throttle positions with the most impact at idle position.

If stock, the pilot jet number determines the fuel height setting. #38 gets 14.5mm and #42 gets 12.5mm.  (Though, I will say I've used 14.5mm on the 78 with good effect using ethanol fuel.)

None of the stock setting apply to applications where the cam, air filter, and exhaust system pressures are no longer original spec.

Slide needle change:
Remove two top cover screws, and top cover.
Remove screw in arm at main shaft
Remove two screws in top well of slide
Rotate lift plate and arm up and clear of slide
use finger to pull slide out of bore
Push needle out of slide from the bottom of slide.
Place E clip in desired position
reverse procedure for reassembly

2 notes:
You WILL need to vacuum synch after doing this.
The two slide screws require a narrow shaft screwdriver and a magnetic tip helps both during extraction and reassembly.