Author Topic: Jetting the CB550 PD series carbs.... (Read 17590 times)

Scott S · « **Reply #25 on:** April 27, 2012, 06:50:52 PM »

Thank you , TT.

Correct me if I'm wrong, but my '78 carbs have the #42 pilot jets and my 13mm setting is pretty darn close....right?

I can't save the pics from the online manual I'm currently referrencing, but when you say "Remove screw in arm at main shaft", do you mean the "link arm fixing screw", as shown in figure K3-5, page 176 in the supplement to the factory manual?
(I only have it as a .pdf and can't copy the pic to post here)

TwoTired · « **Reply #26 on:** April 27, 2012, 07:14:49 PM »

Quote from: Scott S on April 27, 2012, 06:50:52 PM

Correct me if I'm wrong, but my '78 carbs have the #42 pilot jets and my 13mm setting is pretty darn close....right?

Yes. But, I prefer the 14.5 due to the ethanol gas I'm forced to buy. And, I always thought the lean burn settings at the factory to placate the EPA, made the engine run hotter and made the seals and valve guides wear/fail much faster. (The latter could have been oil choice issues, I suppose.) Sure made the fuel economy better, though.

Quote from: Scott S on April 27, 2012, 06:50:52 PM

I can't save the pics from the online manual I'm currently referrencing, but when you say "Remove screw in arm at main shaft", do you mean the "link arm fixing screw", as shown in figure K3-5, page 176 in the supplement to the factory manual?

Yep.

Scott S · « **Reply #27 on:** April 27, 2012, 07:19:24 PM »

Loosen this screw and I should be able to raise the slide(s) to change clip settings, right?

TwoTired · « **Reply #28 on:** April 27, 2012, 08:18:16 PM »

remove the screw

lucky · « **Reply #29 on:** April 27, 2012, 08:41:04 PM »

Then remove the spring.
Then remove the circlip and plastic washer.
Then remove the link from the slide.
Then remove the needle holder down in the slide.
Make sure when you put the needle holder back in the slide that the spring goes right over the center of the needle and not off to one side.

lucky · « **Reply #30 on:** April 27, 2012, 09:03:01 PM »

When you get that all apart can you tell us if it has a needle with more than one groove on it? Thanks.

I was under the impression that 1978's (550's) did not have the adjustable needle.

TwoTired · « **Reply #31 on:** April 27, 2012, 09:12:16 PM »

You do not have to take the lifter mechanism apart. If you have the right screwdriver, the two screws on the slide can be removed and the whole thing swings up and out of the way, granting full access for slide removal.

Scott S · « **Reply #32 on:** April 28, 2012, 04:04:17 AM »

I'll try one this weekend and see if I have adjustable needles. I do have some washers I could put under the clip to raise the needle.

I'm doing all of this because these are the "lean burn" carbs and I've done the aforementioned mods.....bore, cam, headwork, exhaust, etc.
Maybe I should just try the 105 main and 42 pilot and see what happens? Or would it be worth my time to raise the needles?

Than you both for the in depth info. The factory manual supplements don't show this procedure and make it appear that you have to de-rack the carbs to remove the slide assembly.

lucky · « **Reply #33 on:** April 28, 2012, 05:13:56 AM »

Quote from: Scott S on April 28, 2012, 04:04:17 AM

I'll try one this weekend and see if I have adjustable needles. I do have some washers I could put under the clip to raise the needle.

I'm doing all of this because these are the "lean burn" carbs and I've done the aforementioned mods.....bore, cam, headwork, exhaust, etc.
Maybe I should just try the 105 main and 42 pilot and see what happens? Or would it be worth my time to raise the needles?

Than you both for the in depth info. The factory manual supplements don't show this procedure and make it appear that you have to de-rack the carbs to remove the slide assembly.

Remember...just one change at a time.

If you do decide to put a washer under the needle you will need calipers to measure them . The brass washers can vary in thickness .004 even after they have had the burr sanded off of the back side.

Also if there is that little pocket in the bottom of the slide where the needle clip sets,you need to know if the washer you add sits inside the pocket or over the top of the pocket. the pocket is about .012 deep.

Scott S · « **Reply #34 on:** April 28, 2012, 05:19:14 AM »

I have some washers that came in a "jet kit" from Sirius (custom kit with jet sizes I specified...I have 8 different sizes to choose from). I'll be sure to check everything closely if/when I get the slide out.

I have a long ride planned today, so it may be tomorrow before I dig into them.

lucky · « **Reply #35 on:** April 28, 2012, 08:44:02 AM »

Quote from: Scott S on April 28, 2012, 05:19:14 AM

I have some washers that came in a "jet kit" from Sirius (custom kit with jet sizes I specified...I have 8 different sizes to choose from). I'll be sure to check everything closely if/when I get the slide out.

I have a long ride planned today, so it may be tomorrow before I dig into them.

Sounds good. Please give us the full data when you report back. Thanks.
Intake type.
exhaust type.
Jets.
Washers.
Mixture screw.

lucky · « **Reply #36 on:** April 28, 2012, 08:49:45 AM »

Quote from: Elniniomuchachos on November 22, 2011, 11:03:13 PM

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...

When you say the needle jet is set at the highest mark that is very confusing.

Do you mean the needle in the slide?

"set at the highest mark" Does that mean the clip is on the bottom groove?

I cannot imagine being in Arizona and having the needle all the way down with the clip in the top groove. The engine would get hot and run lean.

Let us know. Thanks

Lostboy Steve · « **Reply #37 on:** April 28, 2012, 08:51:16 AM »

This topic has to be one of the most popular on the forum. huh? Well yesterday I adjusted my idle screws to the 1.5 in and now my number 1 carb has a slight drip of gas coming from what seems like the screw? Strange? Any ideas?

lucky · « **Reply #38 on:** April 28, 2012, 08:56:40 AM »

Quote from: twistedengineering on April 28, 2012, 08:51:16 AM

This topic has to be one of the most popular on the forum. huh? Well yesterday I adjusted my idle screws to the 1.5 in and now my number 1 carb has a slight drip of gas coming from what seems like the screw? Strange? Any ideas?

Some misunderstanding.
The mixture screws on the 1978 CB750 would be 1.5 turns OUT from fully closed.
What year is your CB750?

BTW This thread SHOULD be VERY popular, until we get the answers to all of the jetting problems.
I would like to pursue this until we do have SOLID data and all the forum members can have bikes that run right. 1977-78s especially.
But if owners do not report back their results with ALL OF the facts then
many owners will still be riding poorly tuned bikes.

Lostboy Steve · « **Reply #39 on:** April 28, 2012, 08:59:19 AM »

No mine is a 77 550. I talked to you on a separate thread and you advised me to set them to 1.5 out from all the way in, or so I thought.

lucky · « **Reply #40 on:** April 28, 2012, 09:01:59 AM »

Quote from: twistedengineering on April 28, 2012, 08:59:19 AM

No mine is a 77 550. I talked to you on a separate thread and you advised me to set them to 1.5 out from all the way in, or so I thought.

Yes that is correct.
Your quote from above.
"This topic has to be one of the most popular on the forum. huh? Well yesterday I adjusted my idle screws to the 1.5 in and now my number 1 carb has a slight drip of gas coming from what seems like the screw? Strange? Any ideas?"

I just wanted to be clear.
As far as the fuel drip you might want to check the float bowl screws and make sure that float bowl gasket is not leaking. I do not think fuel would leak from the mixture screw unless the rubber O ring is damaged or missing. Is it?
Also hopefully the float level is correct.
Just covering all the bases.

BTW the 77-78 CB750 carbs are almost identical to the 550's but keep in mind the jetting numbers will be sightly different.
When reading the posts lets all be clear about if it is a 550 or 750.

Lostboy Steve · « **Reply #41 on:** April 28, 2012, 09:05:16 AM »

Btw I COMPLETELY AGREE. There should be a base tune chart with jet sizes, adjustments, and needle position, for a given setup.

Lostboy Steve · « **Reply #42 on:** April 28, 2012, 09:06:43 AM »

Quote from: twistedengineering on April 28, 2012, 08:59:19 AM

No mine is a 77 550. I talked to you on a separate thread and you advised me to set them to 1.5 out from all the way in, or so I thought.

Well.... it wasn't, but after turning the screw who knows. I'll have to pull it all the way out when i get home today and re-check. I have extras anyway.

lucky · « **Reply #43 on:** April 28, 2012, 09:10:00 AM »

Quote from: twistedengineering on April 28, 2012, 09:05:16 AM

Btw I COMPLETELY AGREE. There should be a base tune chart with jet sizes, adjustments, and needle position, for a given setup.

Yes that would be great wouldn't it? We can share information, and I will do it.
(put together the chart)

TwoTired · « **Reply #44 on:** April 28, 2012, 11:10:49 AM »

Quote from: twistedengineering on April 28, 2012, 08:51:16 AM

This topic has to be one of the most popular on the forum. huh? Well yesterday I adjusted my idle screws to the 1.5 in and now my number 1 carb has a slight drip of gas coming from what seems like the screw? Strange? Any ideas?

The IMS for the PD carbs have an oring for them, which is squished tight by a spring and flat washer. If it is leaking, you have two choices: New orings, or increase the spring tension.

While I'm here...

I checked the needles on my PD46C set an they are adjustable. They have E2349F stamped on them. FWIW

lucky · « **Reply #45 on:** April 28, 2012, 11:32:44 AM »

Quote from: TwoTired on April 28, 2012, 11:10:49 AM

Quote from: twistedengineering on April 28, 2012, 08:51:16 AM
This topic has to be one of the most popular on the forum. huh? Well yesterday I adjusted my idle screws to the 1.5 in and now my number 1 carb has a slight drip of gas coming from what seems like the screw? Strange? Any ideas?
The IMS for the PD carbs have an oring for them, which is squished tight by a spring and flat washer. If it is leaking, you have two choices: New orings, or increase the spring tension.

While I'm here...

I checked the needles on my PD46C set an they are adjustable. They have E2349F stamped on them. FWIW

So is it a 1977 550?

TwoTired · « **Reply #46 on:** April 28, 2012, 11:36:26 AM »

Quote from: lucky on April 28, 2012, 11:32:44 AM

Quote from: TwoTired on April 28, 2012, 11:10:49 AM
I checked the needles on my PD46C set an they are adjustable. They have E2349F stamped on them. FWIW

So is it a 1977 550?

PD46C series carbs were issued with the 1978 CB550K model.

lucky · « **Reply #47 on:** April 28, 2012, 03:31:12 PM »

Thanks for that info Two Tired. i will add it to the chart i am building.
BTE...
Did you see this post the other day?
http://forums.sohc4.net/index.php?topic=105797.0
Go down to reply #6

Very interesting dyno and a/f ratio data.

Scott S · « **Reply #48 on:** April 29, 2012, 03:28:02 PM »

Thanks to your help, TT and Lucky, we figured out how to change the needle settings.
TT, the needles are the same as yours and the clips were in the 2nd groove from the top.
We moved them down one notch to the middle groove.

I really hope I'm close because those carbs are a royal PITA to get on the bike!! Much worse than the early bikes, IMO.

Scott S · « **Reply #49 on:** May 01, 2012, 12:36:09 PM »

Well, got her started today and she runs well. Had some fuel overflow issues at first, but they've stopped. I'm guessing dry, stick floats and/or needles at first. It no longer overflows at all.
No intake leaks, no hanging idle, etc. I played with one of the outer IMS screws and it seemed to like 1.5 best, which is where they all are set. I have not done them individually yet. Those things are a PITA to get to on the PD series carbs.

I set the float height at 13mm, raised the needle one clip, kept the 42 pilot and went from a 90 to a 105 on the main.

The plugs look just a tiny bit on the lean side to me. They're not white, but they are on the whiter side of tan. In real life, imagine them just a tiny, tiny bit more white than this. Very clean, no soot, very clean on the porcelain.
Whatta ya think? I do need to get the snorkel back on the air box and clean/oil the Uni-Filter element.

#1 plug

#4 plug

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Author Topic: Jetting the CB550 PD series carbs.... (Read 17590 times)