Author Topic: 1975 CB550 Carb overhaul / cleaning / rebuild (Read 7292 times)

eprovenzano · « **on:** April 30, 2015, 09:10:23 AM »

My Son-in-law bought 75 CB550 two years ago. It was / is in stock pristine condition. Honestly its in such good shape he doesn't have the heart to cafe it... even thought that was the original intent when he purchased the bike. As things happen, life sometimes gets in the way of ride time and bikes sit. Prior to the 1st winter I suggested fuel stabilizer, no he didn't listen to me. After the 1st winter when he pulled the bike out it ran pretty good, but not like it did before storage. He then attempted to use an aftermarket air filter, not good. It simply was allowing too much air in and the bike was running lean. He went back to a stock filter, better, but not like it should be. I ran some seafoam through and got it to run better with some air / fuel screw adjustments. Again when the bike was parked over winter months, no stabilizer was used... yea not good.

He now wants to get the bike running properly again. The bike was brought to my house so I can make sure all is well... After sitting all winter, without fuel stabilizer, I did get the bike to start... but yep she's got issues... rough idle, and would not rev out. Since the tires are bald, we will also be replacing the tires and tubes.

So far, I've pulled the carbs, and dismantled one of four. On the 1st carb, I've found the main jet plugged, pilot jet partially clogged, emulation tube (jet) pretty clean, floats and float needle clean, but lots of dirt in the bottom of the bowl. I still need to pull the needle from the slide, to record needle number and clip position. I also need to write down the main jet and pilot jet sizes, as well as the position of the air screw, and then compare all this data to the stock setting. The intake (carb to intake) boots are in great shape considering their age. The carb to airbox boots show some age as two are torn and will be replaced.

While things are apart, the plans are to check the valves, put in a new set of plugs and scrub / clean everything years of dirt and grime needed to be removed.

After doing a lot of reading / research the only thing internally in the carb I may want to replace is the main jet and float seat o-rings. To my eye they look fine, but... I don't know how old they are so better safe than sorry. I do not plan to remove / disturb any other parts of the carbs to create more work for myself than is necessary. Cleaning will be done with spray carb and brake cleaner, followed with WD40 and compressed air. So far I've opened the main jet open, and freed the clog in the pilot jet, but I still have lots of cleaning to do.

That's the plans for now... am I missing anything, should I be doing more / less... Just looking to confirm I'm on the right path. Also I see the the o-rings I need are Main jet 1.2mm CS x 3.5mm ID, Float Seat 1.5mm CS x 5 mm ID. Has anyone had success sourcing them at an auto part store?

streak09 · « **Reply #1 on:** April 30, 2015, 12:20:52 PM »

I just finished up my carb rebuild, so this is fresh in my head. I'm not sure what type O-rings auto-parts stores have, or local hardware, but I believe what you should look for is Buna-N (Nitrile) O-rings. These are fuel resistant and will hold up well in gasoline. I purchased all mine through the "The O-Ring Store" . I purchased every O-ring (Buna-N 90) in the carbs except the float bowls, I purchased a set of formed ones off ebay for those. Everything fit fine, and it wasn't very expensive. I would suggest looking for some of the formed float bowl O-rings, getting unformed to seat correctly and not pinch when putting the bowls back on takes something just short of an act of God (for me anyways).

Other suggestions would be to check float height, as it seems this has played havoc with a lot of folks. Definitely replace boots if torn, air leaks will greatly affect performance.

I don't have much experience on SOHC4s, but quite a bit on smaller bikes.

Good Luck!

Duanob · « **Reply #2 on:** April 30, 2015, 12:34:06 PM »

I would just buy the Honda carb gasket kits and know that you have the proper ones. They aren't too expensive. If you need jets later on you can buy them at jetsrus.com for cheap.

Also if you have crud in the bowls you probably have crud in the fuel tank as well. I would put on the list to clean the tank and fuel tap in-tank filter.

Tews19 · « **Reply #3 on:** April 30, 2015, 07:16:46 PM »

Never replace the jets unless they are damaged or not the original ones from when the bike rolled off the show room. You can get o ring kits on ebay for like 15 bucks.

calj737 · « **Reply #4 on:** May 01, 2015, 07:12:05 AM »

+2 on cleaning the tank. Debris in the bowls comes from the fuel upstream and without purifying the source, the recipient (carbs) will constantly clog. +2 on stock brass.

Forget the WD-40 for cleaning. Use carb cleaner or Brake cleaner. You want something that evaporates, not dilutes.

Rgconner · « **Reply #5 on:** May 01, 2015, 08:14:35 AM »

Starter fluid works a treat =)

Better than the Cal-EPA compliant brake cleaner.

Honestly its in such good shape he doesn't have the heart to cafe it... even thought that was the original intent when he purchased the bike.

I came to the same conclusion on my CB550. Read up on HondaMan's threads for ways to make it more functional and reliable. Electrical is the weak spot on this bike, and that is what is most likely to strand you.

eprovenzano · « **Reply #6 on:** May 03, 2015, 12:33:17 PM »

Plans are to clean jets and reuse. I will replace the o-rings on the main and float valve. I finally had a little time to pull the numbers off the jets and needle.

The PJ is a 38, MJ is a 100, and the needle is a (I think, damn numbers are so small) 272304, with the clip on the 1st top notch. A/S was 1.25 turns out. (I set the A/S last year when trying to get the bike to run better)

Based on the clip position, to me thats too lean... but I need to research a little more. New air box to carb boots have been ordered. At this point I'm ready to dive in and really scrub the carbs. If the jets check out, and needles are good, (no reason their not) I hope to have the carbs back on the bike in a week.

eprovenzano · « **Reply #7 on:** May 04, 2015, 06:39:32 AM »

I pulled the plugs, and they looked pretty good. They were brown to white which to me is good to slightly lean. So after some research, I'm going to drop the clip from the 1st notch to the 2nd one. I talked to my son-in-law, and he felt the power was a little flat on top. Now is that from clogged main jets (probably), is it from the needle being too lean (maybe, but I'm sure it didn't help).

I just need to order the o-rings and while I'm waiting, I'll start the cleaning process.

seanbarney41 · « **Reply #8 on:** May 04, 2015, 07:08:04 PM »

sounds like you are on the right track...I think WD40 is actually a really good cleaner/degreaser...actually about all it is really good for, but not really strong enough for carb duty. I will use it to displace the corrosive carb cleaners, though. Don't forget to bench sync. I also encourage you to bench set the fuel level in the bowls via the clear tube method. Many have found that the traditional float measurement no longer applies with repro float needles, over adjusted bent up float tangs, and possibly even differences in the specific gravity of modern fuel.

eprovenzano · « **Reply #9 on:** May 05, 2015, 06:47:43 AM »

Thanks guys... I just ordered some replacement o-rings (main jet and float seat) from the o-ring store. While I wait their arrival, I'll get to cleaning and documenting the current jets, needle, and clip position is the rest of the carbs. Just want to make sure they are all the same (hey after 40 years, you never know...)

eprovenzano · « **Reply #10 on:** May 06, 2015, 06:38:09 AM »

I finished pulling all the carbs apart last night. I've been keeping all the parts separated so they go back into the carb they came out of. I've found 2 out of 4 really varnished, with the MJ and PJ clogged. One was spotless, and one has just a little dirt in the bowl.

The slides on the 1st carb came apart with no issues... the 2nd... not so much, one screw will not let go... the third the same thing and the 4th came apart after some proper cursing...

With the needles set on the top notch (too lean) I need to get these apart so the clip position can be changed. I've decided to drop the clip to the 3rd notch, (FYI stock is the 4th notch) All carbs have a 38 PJ and a 100 MJ

Just need to pick up some carb and brake cleaner, along with some WD40, so the cleanup can begin. I hope to have everything cleaned and somewhat re-installed in the carbs before the new 0-rings arrive.

Duanob · « **Reply #11 on:** May 06, 2015, 08:59:04 AM »

A carb cleaning kit works well (different size wires) and canned air with the straw is great for blowing out narrow passages and seeing if they are clear. be careful not to blow carb cleaner in your eyes!

I would bet cleaning the clogged jets will make a huge difference. BTW why not set the needle to stock? I would guess the PO set it that way to compensate for dirty carbs. The needle holders have to be turned 90 degrees to be removed from the slides. As far as the tiny screws that hold it together I use a magnetic screw bit holder and a 2" long philips bit. Those things are tiny and easy to lose. Good luck.

Deltarider · « **Reply #12 on:** May 06, 2015, 10:07:54 AM »

Quote

Those things are tiny and easy to lose

Easy to lose? Easy? Well, that's not my experience.

eprovenzano · « **Reply #13 on:** May 06, 2015, 11:04:59 AM »

Quote from: Duanob on May 06, 2015, 08:59:04 AM

A carb cleaning kit works well (different size wires) and canned air with the straw is great for blowing out narrow passages and seeing if they are clear. be careful not to blow carb cleaner in your eyes! I would bet cleaning the clogged jets will make a huge difference. BTW why not set the needle to stock? I would guess the PO set it that way to compensate for dirty carbs. The needle holders have to be turned 90 degrees to be removed from the slides. As far as the tiny screws that hold it together I use a magnetic screw bit holder and a 2" long philips bit. Those things are tiny and easy to lose. Good luck.

I have two of the 4 slides apart... 2 each with a screw I cannot get loose... I'll try a few more "tricks" to try and remove the stuck screws. I keep thinking I will take it all the way back to stock jetting, (4th clip) since I know everything will be clean and set up correctly.

Duanob · « **Reply #14 on:** May 06, 2015, 11:20:29 AM »

Quote from: Deltarider on May 06, 2015, 10:07:54 AM

Quote
Those things are tiny and easy to lose
Easy to lose? Easy? Well, that's not my experience.

Considering you never vac sync your carbs, I assume you never pull the slaides apart, I guess you will never lose those screws!

Deltarider · « **Reply #15 on:** May 06, 2015, 11:21:36 AM »

Have you read this reply elsewhere? http://forums.sohc4.net/index.php/topic,147468.msg1679429.html#msg1679429

TyMatthews · « **Reply #16 on:** May 06, 2015, 12:46:30 PM »

Be careful with the carb cleaner around any rubber bits, particularly o-rings... depending on the nature of the solvent in your cleaner of choice, you could end up causing the rubber to swell quite a bit, to the point they no longer fit. Also, please consider wearing eye protection and ensure you're spraying in a well-ventilated area. Install a fan nearby to suck that stuff out into the atmosphere. Solvents that work great on built-up hydrocarbon gunk are typically very bad for humans and other living organisms.

Deltarider · « **Reply #17 on:** May 06, 2015, 11:42:22 PM »

Quote

Considering you never vac sync your carbs,

Who said 'never'? The way I bench sync, I do not need the vacuum meters although I sometimes use them to check afterwards. So far I've always managed to bench sync the carbs within 2 cm Hg of each other which is well within factory specs.

Quote

I assume you never pull the slaides apart, I guess you will never lose those screws!

The only time I did this - for experimental reasons I dropped the needles from 3rd notch (as prescribed in Europe) to 4th (as prescribed in US) - I couldn't losen two of the screws and had to bring the rack to the dealer to have him do them. I've learned that others have experienced the same.
My advice: make sure you use the right type of screwdiver, concentrate and press well. Do it right in the first attempt. If not, you may ruin that little screw and you'll have a problem.
All in all, I wouldn't say they are easy to losen and I therefore thought it wise to warn. Maybe you could make yourself useful by advicing us what type of screwdriver to use: is it really Phillips or is it JIS... ?

DaveBarbier · « **Reply #18 on:** May 07, 2015, 04:37:21 AM »

Those tiny screws are JIS, not Phillips. Before trying to really press hard and get the last couple screws out, I'd check the fitment of your driver with one of the screws you already removed. If it doesn't fit perfectly then you're very close to stripping out the screws. You should DEFINITELY go get some JIS drivers if you don't already. They'll grip much better than Phillips. Phillips drivers are designed to "cam out" of a screw to prevent over tightening.

Also, I agree with Duanob questioning altering needle position from stock. Clean the carbs, stock jetting, needle position and IMS, bench sync, test on the bike.

---
1978 Honda CB550K

Jimsun · « **Reply #19 on:** May 07, 2015, 06:10:14 AM »

Simple green works wonders.

eprovenzano · « **Reply #20 on:** May 07, 2015, 07:02:43 AM »

Quote from: DaveBarbier on May 07, 2015, 04:37:21 AM

Those tiny screws are JIS, not Phillips. Before trying to really press hard and get the last couple screws out, I'd check the fitment of your driver with one of the screws you already removed. If it doesn't fit perfectly then you're very close to stripping out the screws. You should DEFINITELY go get some JIS drivers if you don't already. They'll grip much better than Phillips. Phillips drivers are designed to "cam out" of a screw to prevent over tightening.

Also, I agree with Duanob questioning altering needle position from stock. Clean the carbs, stock jetting, needle position and IMS, bench sync, test on the bike.

---
1978 Honda CB550K

I did not know about the JIS screws... I was using a good Phillips screwdriver, but I will pick up the proper tool this evening. Thanks for thew tip.

I agree with everyone and will set the needles to stock. It's just hard to understand why a PO had the clips on position 1...

My order for o-rings should be in today... If life doesn't get in the way, I hope to be cleaning / scrubbing the cards and have them reassembled sometime over the weekend. Yes bench synced, and then vacuum synced..

I have more research to do about proper syncing of the carbs, but one step at a time...

DaveBarbier · « **Reply #21 on:** May 07, 2015, 07:43:49 AM »

POs do crazy things sometimes. And it's probably worth a mention, but before a vacuum sync I'd go run through the cam chain, tappet clearance, plug gap, point gap and timing (idle and advance) adjustments just to make sure it's good to go. Sync is the last thing that should be done. Good luck!

---
1978 Honda CB550K

Deltarider · « **Reply #22 on:** May 07, 2015, 10:40:42 AM »

Quote

Those tiny screws are JIS, not Phillips.

Good. Glad we've settled that.

Quote

I agree with everyone and will set the needles to stock.

Have you verified your model by checking the engine- and framenumber as I suggested? http://forums.sohc4.net/index.php/topic,147468.msg1679429.html#msg1679429

Quote

It's just hard to understand why a PO had the clips on position 1...

Most probably a member of this forum.

eprovenzano · « **Reply #23 on:** May 28, 2015, 06:35:01 AM »

Just wanted to update... Life keeps getting in the way of bike repairs... but carbs have been cleaned, new O-rings on main jet and float, reassembled and bench synced. Next will be to reinstall carbs air box etc, and then set up for a vacuum sync. I still need to build a DIY a manometer.

eprovenzano · « **Reply #24 on:** May 29, 2015, 08:02:19 AM »

The freshly bench synced carbs are back on the bike... Taking the carbs off for the 1st time was a pain in the arse... but once you learn the proper procedure of how to put them on and off, it gets a lot easier. I still need to put the airbox boots on, button up a few more things before I'm ready to add fuel. Knowing my son-in-law will want to take a ride as soon as its fired up, I pulled the rear tire as it bald.. new tires and tubes are waiting to be mounted. Without the rear tire, I can start the bike, make any adjustments to the engine I deem necessary and he cannot ride the bike until the new tires are installed...

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Author Topic: 1975 CB550 Carb overhaul / cleaning / rebuild (Read 7292 times)