Topic: 1975 CB550K Restoration

[HondaAddict]

Bike of the Month!

Thanks!

[Sam Green Racing]

Hi HondaAddict...I nominated you for bike of the month and you were seconded.  You must go here to accept the nomination.
forums.sohc4.net/index.php/topic,172969.msg2015722.html#new

Done. Thanks for the nomination!

I'll have to go read the rules as I understand I'm supposed to include a bit more info about the bike. Will do that as soon as possible.

Add details once the voting thread opens.
That's a nice looking bike and will probably get my vote despite me preferring sports and race bikes.

Sam.
 

[HondaAddict]

I'm pretty sure I need to change jets. I try to not ask questions here before searching this site for the answer. I've done that, but I'd be happy to have the opinions of others here before I order new jets.

It backfires on deceleration and sputters when I open the throttle ~1/8th. From what I've read here, these are signs that it's running lean. Here's a photo of one plug (they all look about the same).



It works very good at any throttle position after it gets past this stumble, so I assume I'm good on the main jet.

I've checked/tested/adjusted the usual causes suggested on other threads here. Timing & advance, points, wires, coils, float heights, fuel flow, emulsion tubes, exhaust/intake leaks, and the list goes on. I've adjusted the idle air screws in 1/8 turn increments from 3/4 turn (when it stalls) up to 3 turns (which can't be right). It backfires at all IAS settings, although it sputters less as they're backed out further. 

Here's the setup:

• Stock air box with new UNI foam filter
• Delkevic 4-into-1 exhaust
• New NGK DR7EA plugs and NGK 10k caps
• New #38 and #100 Keihin jets

Should I try #40 slow jets? Or larger?

[seanbarney41]

Plug color is perfect.  What kind of work has been done to the ignition advancer?

[RAFster122s]

Sounds like the carbs are not clean and the mixture coming off idle goes lean.  Jetting with that exhaust Might be an issue, but I do not think I have heard anyone mention they needed to play with the jets before, just the carb adjustments.
These carbs can still let the bike run in amazingly bad condition for the carbs.
Is the Uni oiled? It takes very very little oil for the UNI filter and it typically will run richer with one in use, not leaner.

What needle position and how many turns out are you on the air screws?

[HondaAddict]

Thanks, everyone. Here are answers to your questions:

Plug color is perfect.  What kind of work has been done to the ignition advancer?

No work on the advancer - just removal and inspection. It seems to be advancing properly. I even checked it using a second timing light.

Sounds like the carbs are not clean and the mixture coming off idle goes lean.  Jetting with that exhaust Might be an issue, but I do not think I have heard anyone mention they needed to play with the jets before, just the carb adjustments.
These carbs can still let the bike run in amazingly bad condition for the carbs.
Is the Uni oiled? It takes very very little oil for the UNI filter and it typically will run richer with one in use, not leaner.

What needle position and how many turns out are you on the air screws?

Carbs have had a thorough overhaul and appear clean, but maybe I missed something. I've had them out twice in the past week. I'll pull them again, as I know "carbs are clean" is something people often say before discovering it's not the case. Aside from the jets, are there any other passages/circuits I should suspect?

The filter is oiled. For the heck of it, I tried the old paper filter and it made no difference.

It was running fine before this project, so I didn't move the needles. Just can't remember what setting they're on now. I'll look at those as well.

On the air screws, I went for a ride and adjusted them 1/8 turn every little while. I did this from 3/4 to 3 turns. The sputtering is less severe as I back out the screws beyond ~2 turns, but it never goes away. And the backfiring on decel is always there. The above photo was taken at ~3 turns, which I figured is too far out.

If anything, I'd expect the fuel level to be a bit low barring anything out of spec with the ignition advancer. I doubt seriously that the exhaust with the stock airbox is causing any issues.

I'll check float levels and advancer again. Could low fuel level also cause backfiring on decel?

[HondaAddict]

Yes, as that would indicate a lean condition (just like the stumble might be related to the same issue). Clear Tube method for fuel level is best. No need to pull the carbs yet. Check the level. If they're good, drop each bowl individually and make sure a carb hasn't dropped its jet  The o-rings on the jets sometimes are too small and don't keep the jet in place.

Will do. I haven't tried the clear tube method as I don't have a nipple for the bowl drains. I have about 20 lbs of old brass fittings in a box, but none are metric.

[HondaAddict]

you can get small plastic vacuum nipples at the auto parts store and those will fit. Or, just jam the clear tubing into the drain hole. OR, get a piece of brass tube the correct diameter and use a die and thread the OD a couple of turns. Doesn't take a whole lot of engagement. 

Thanks, this is very helpful info. I’ll see what I can gear up.

[seanbarney41]

Often, advance springs have gotten weak causing too early advance, which can affect off idle performance.

[RAFster122s]

Check the petcock bowl screen, it is crucial that it is clean, lest it slow the carbs refilling.  Air passages and jet passages in the carb have to all be clear.  It has been forever since I had my 550 carbs apart...

[HondaAddict]

Often, advance springs have gotten weak causing too early advance, which can affect off idle performance.

Thanks, I'll have a closer look. Now that you mention this, I recall reading on other threads that some people have shortened them.

Check the petcock bowl screen, it is crucial that it is clean, lest it slow the carbs refilling.  Air passages and jet passages in the carb have to all be clear.  It has been forever since I had my 550 carbs apart...

Thanks. The petcock is all good - I installed a new OEM rebuild kit a few days ago. When the carbs come off, I'll be looking closely at all passages. Damned if I want to miss something again.

-----------------------------------------------------------------------------------------------------------------------------

It was nice here Friday so I took my V65 Sabre for a 500 km run along twisty coastal roads. It's supposed to rain all weekend, so I'll get back to the real world and tackle this problem. Based on the helpful advice y'all have given me, here's my to-do list:

• Check advancer springs
• Re-check timing & advance
• Clear tube test
• Pull off bowls and check for loose jets, adjust floats if necessary
• If no joy thus far, pull the carbs
• Check/clean jets, emulsion tubes and passages
• Check needle positions
• Double-check float heights
• Reinstall carbs and pray to the motorcycle gods

[HondaAddict]

Clear tube test.



I've read here that the fuel level should be 2-4 mm below the gasket line. Is #2 a little low? Is #4 too high?

[seanbarney41]

3 and 4 are high, actually surprised you are not seeing sooty plugs on 3 and 4

[HondaAddict]

Often, advance springs have gotten weak causing too early advance, which can affect off idle performance.

I rechecked the advancer. There was the tiniest bit of slop in the springs at idle position. I bent the spring ends slightly to tighten them up. The gaps between the spring coils show they're now under tension, so I'll call this task done and set the timing again.



Can't test any of this today due to weather. Might as well pull the carbs...

[HondaAddict]

The clips for all needles are in the fourth slot from the top.

[RAFster122s]

Are all your brass in the carb genuine K or is any aftermarket?

[Little_Phil]

If I’m not mistaken, they should be second from top. The slot number is counted from tip, not top. The lower the clip, the richer the mixture.

To add to your confusion HondaAddict this info has been around on this site for a while. I do not know of its source or authenticity.

[HondaAddict]

If I’m not mistaken, they should be second from top. The slot number is counted from tip, not top. The lower the clip, the richer the mixture.

Thanks. If a lower clip position is richer (which makes sense), would raising them worsen my problem?

Are all your brass in the carb genuine K or is any aftermarket?

Yes, all new Keihin jets and other parts are from Honda carb rebuild kits.

To add to your confusion HondaAddict this info has been around on this site for a while. I do not know of its source or authenticity.

Thanks. I do recall seeing this before but hadn't looked at it recently. Now that I look again, I notice it says I should be running #40 slow jets. I'm running #38s, because the online parts fiches show #38s. I have a clean set of #40s. I wonder if I should give them a try?

[Cobalt Kid 60]

Hello Honda addict.

Just joined this forum and looked and read your restore of your 550. Awesome job to say the least.

[HondaAddict]

Hello Honda addict.

Just joined this forum and looked and read your restore of your 550. Awesome job to say the least.

Thanks. And welcome to the forum!

[Stretch]

It was nice here Friday so I took my V65 Sabre for a 500 km run along twisty coastal roads. It's supposed to rain all weekend, so I'll get back to the real world and tackle this problem. Based on the helpful advice y'all have given me, here's my to-do list:

V65 Sabre is probably one of the best values in big bikes anywhere. You can buy one cheap, ride the daylights out of it and sell it for almost what you paid. Ive had mine for about 10 years and plan on wearing it out. In those years I've put about 45,000 miles on it (about 70 grand on the clock)and its been a pleasure to ride. My Magna has about 75,000 miles on it. They got a lot of bad press back in the day but those problems could be overcome and they have only left me stranded once and it was more my fault than the bikes. Yes they're a bit on the heavy side but that helps to make them great road bikes. They're not the fastest bikes on the road anymore but they can more than hold its own. After riding with several groups over the years I've had people ask me several times is, "What is that thing?"

...Back to the regularly scheduled program...

You sure did a great job on your restore. My CB750 is low miles but it wasn't stored the best for its life time. You are to be congratulated on your project. It sure came out nice! Problem is, you've raised the bar a little higher than I'll ever be able to clear. Well Done!

[HondaAddict]

It was nice here Friday so I took my V65 Sabre for a 500 km run along twisty coastal roads. It's supposed to rain all weekend, so I'll get back to the real world and tackle this problem. Based on the helpful advice y'all have given me, here's my to-do list:

V65 Sabre is probably one of the best values in big bikes anywhere. You can buy one cheap, ride the daylights out of it and sell it for almost what you paid. Ive had mine for about 10 years and plan on wearing it out. In those years I've put about 45,000 miles on it (about 70 grand on the clock)and its been a pleasure to ride. My Magna has about 75,000 miles on it. They got a lot of bad press back in the day but those problems could be overcome and they have only left me stranded once and it was more my fault than the bikes. Yes they're a bit on the heavy side but that helps to make them great road bikes. They're not the fastest bikes on the road anymore but they can more than hold its own. After riding with several groups over the years I've had people ask me several times is, "What is that thing?"

...Back to the regularly scheduled program...

You sure did a great job on your restore. My CB750 is low miles but it wasn't stored the best for its life time. You are to be congratulated on your project. It sure came out nice! Problem is, you've raised the bar a little higher than I'll ever be able to clear. Well Done!

Thanks! As you know, there are some incredible bikes and projects on this site, so I felt the bar was already unreachable for me. This truly is a great site to visit when you need inspiration.

And I couldn’t agree more about the Sabre and other V4s. They were years ahead of their time. They’re no longer king of the hill, but they’re still very impressive to ride. I had a friendly street drag with a Harley (don’t know what model) a few weeks ago and it wasn’t even close. I slowed down after about a half mile and he pullled up beside me, looked a couple of times at my side cover to figure out what I was riding, then gave me a thumbs up. These bikes get a great deal of respect from people who know about them. It’s a nice feeling to be cruising along the highway at 75 mph, listening to that low V4 rumble and knowing you have more torque at your disposal than you could ever need. My garage is getting full, but I can’t imagine ever parting with old “Sully”!

[RAFster122s]

Bump...rich condition solved moving needle clips?
David

[HondaAddict]

Bump...rich condition solved moving needle clips?
David

Thanks for asking. I haven't yet moved the clips. I've adjusted the floats (clear tube test shows all are now good) and installed new spark plugs. Still no joy. I've been busy with work so I haven't tried anything else, but I hope to move the needles in the next few days.

[Stretch]

It was nice here Friday so I took my V65 Sabre for a 500 km run along twisty coastal roads. It's supposed to rain all weekend, so I'll get back to the real world and tackle this problem. Based on the helpful advice y'all have given me, here's my to-do list:

V65 Sabre is probably one of the best values in big bikes anywhere. You can buy one cheap, ride the daylights out of it and sell it for almost what you paid. Ive had mine for about 10 years and plan on wearing it out. In those years I've put about 45,000 miles on it (about 70 grand on the clock)and its been a pleasure to ride. My Magna has about 75,000 miles on it. They got a lot of bad press back in the day but those problems could be overcome and they have only left me stranded once and it was more my fault than the bikes. Yes they're a bit on the heavy side but that helps to make them great road bikes. They're not the fastest bikes on the road anymore but they can more than hold its own. After riding with several groups over the years I've had people ask me several times is, "What is that thing?"

...Back to the regularly scheduled program...

You sure did a great job on your restore. My CB750 is low miles but it wasn't stored the best for its life time. You are to be congratulated on your project. It sure came out nice! Problem is, you've raised the bar a little higher than I'll ever be able to clear. Well Done!

Thanks! As you know, there are some incredible bikes and projects on this site, so I felt the bar was already unreachable for me. This truly is a great site to visit when you need inspiration.

And I couldn’t agree more about the Sabre and other V4s. They were years ahead of their time. They’re no longer king of the hill, but they’re still very impressive to ride. I had a friendly street drag with a Harley (don’t know what model) a few weeks ago and it wasn’t even close. I slowed down after about a half mile and he pullled up beside me, looked a couple of times at my side cover to figure out what I was riding, then gave me a thumbs up. These bikes get a great deal of respect from people who know about them. It’s a nice feeling to be cruising along the highway at 75 mph, listening to that low V4 rumble and knowing you have more torque at your disposal than you could ever need. My garage is getting full, but I can’t imagine ever parting with old “Sully”!

I had one of those friendly runs with a Challenger the other day. It was one of those two lane turn lanes with the second lane merging into one. He was behind me so I don't know what kind it was but he decided he wanted to go around me before the lanes converged. I wasn't going to have any of that. I opened the magna up and pulled away. We gave each other the thumbs up as I was turning into my neighborhood.
I'll have to say, if there is a sleeper bike anymore its the magna. People just assume they are harleys so it's easy pickings. I still get, "what is that thing?"

My FIL said he raced a HD up this long hill years ago and got to about 90 by the top, that was on his (now mine) CB750, I said that I use that hill to see how my V4s are running. I should be about 120 by the top. "Your bikes will go that fast?" I said that's 4th gear, I got two more. I do enjoy the CB but when I have the urge to go fast, its on a V4.

I just love riding old bikes. I love the nostalgia and the sound of them. Nothing sounds like the CB with four pipes sticking out the back.

Time to go warm up the old iron for the trip to work. Question is, which one?