Topic: 76' CB550K WON"T IDLE! Not the carbs?

[Azaswas]

Hello all. I'm a long time lurker, first time poster. Fairly recently I traded a Ford Taurus for my first bike a 76' CB550K! I've already replaced the front brake assembly,  from an eBay purchase. I've also tracked down a front blinker lens. When I got the bike, I attempted to ride it home, the PO said it idled high, and that "it took forever, but i finally got the carbs down"... Well, It was running terrible and about 5-8 miles in, it slowly died (presumably from overheating). I trailer-ed it home. Here is the issue, which i haven't seen exactly on here, or on any other forums before.

Bike starts every time.
If its cold, choking it to get started and then afterwards turning choke off. (works like normal)
The bike will  Idle at about 3,500 RPM
Adjusting the idle screw will bring the idle down, but lowering it what-so-ever just lets it drop slowly until it dies.
If you do this, and then turn it back up as its falling, it will idle at the spec 1,000 rpm.
Then if you give it any gas, it will again stay at 3,5000


My first thought was that the PO had f-'ed up the carbs. So I purchased 4x rebuild kits and took those bad boys off. When I pulled them apart, I think i was right to an extent. The bowls were pretty dirty, and the floats were ALL SORTS OF MESSED UP. One float was even missing a float, like of the two, one plastic float was gone. Most were bent utterly out of whack. None of the jets had their o-rings. ect ect. The PO also had made homemade Air-pods with what i could assume was pantyhose.

I managed to find 90% of the stock air system off eBay and local parts places, and after completing the carb rebuilds, running to my local Honda power-sports dealer for the funky mm fuel line, bench syncing the carbs with a dill bit, installing everything back together I was ready to test it out.

It runs EXACTLY the same as before. It's as if I hadn't touched the carbs.

I've tried to look for bindings, or catching on any of the throttle linkage. But It seems that I have to manually turn the throttle, the throttle wont SNAP back, even with a strong spring and no bindings/linkage issues. The other thing is that my secondary jets, I read on here call for a 40, all I have are 38's but the 38's I have and the original 38's I found in the carbs both look way different.


If anyone has any input, suggestions, comments, or helpful ideas, they would be greatly appreciated.

Thank you for your time. Tuyen and Carl. 

[RAFster122s]

Original brass will be marked with the Keihin K and will perform well. Sometimes POs will drill jets rather than buying new brass. So,it is difficult to tell if your brass has been messed with.  Aftermarket carb kits and their brass is incorrect and cause all sorts of running issues.

Normally a 3500 rpm idle issue is a good sized air leak. There are O-rings on the carb intake manifold to head that go bad and original carb intake to carb body rubbers canto bad with air leaks at the clamps.  Some starter fluid sprayed at the intake to head and around the carb rubbers will tell you if you have a leak by the change in running.

Sudco has genuine Keihin brass.

Worth considering buying new brass after eliminating other potential causes for your running issues.
David

[enwri]

As well as all your other problems, timing advance being sticky can make things worse as well, check for loose springs. (wont retard until under 1000, back off idle to get lower than 1000, advance returns to retard, now have to up idle to run at full retard. First time it revs again it's stuck at full advance plus high idle setting. Cycle repeats.

[calj737]

And replace both of your carb cables. Likely they’re rusted up inside preventing the cable to move freely through the sheath. But you should also check the minute space at the throttle housing to the brake perch. You want about a credit cards worth of gap.

[Scott S]

 And dont operate the choke backwards.

[ashkiebear]

As well as all your other problems, timing advance being sticky can make things worse as well, check for loose springs. (wont retard until under 1000, back off idle to get lower than 1000, advance returns to retard, now have to up idle to run at full retard. First time it revs again it's stuck at full advance plus high idle setting. Cycle repeats.

I agree with checking your timing advance, I had a similar problem when I first got my bike and after cleaning up the advancing plate she purred like a kitten.

[Azaswas]

Original brass will be marked with the Keihin K and will perform well. Sometimes POs will drill jets rather than buying new brass. So,it is difficult to tell if your brass has been messed with.  Aftermarket carb kits and their brass is incorrect and cause all sorts of running issues.

Normally a 3500 rpm idle issue is a good sized air leak. There are O-rings on the carb intake manifold to head that go bad and original carb intake to carb body rubbers canto bad with air leaks at the clamps.  Some starter fluid sprayed at the intake to head and around the carb rubbers will tell you if you have a leak by the change in running.

Sudco has genuine Keihin brass.

Worth considering buying new brass after eliminating other potential causes for your running issues.
David

I have no frame of reference to determine if the original ones were drilled, although I might suspect it considering they and the aftermarket ones are both size 38, but are wildly different. A few days ago i tried using some starter fluid around the carb boots, but didn't hit the intake real hard. I will give this a try today!

I emailed sudco last night about the jets, and the response was "The Keihin genuine versions of those jets are only available through Honda. We do have reproduction versions but sold out on the size 40 till November. We do have 38 and 42 sizes in stock. They sell for $4.35 each."

I'm fine with trying those. But I've had good luck with jetsrus, and they have the size 40 in stock. https://www.jetsrus.com/a_jet_kit_street/honda_550_CB550K_1974-1976.htm
Do you have any strong opinion on how I should proceed?

As well as all your other problems, timing advance being sticky can make things worse as well, check for loose springs. (wont retard until under 1000, back off idle to get lower than 1000, advance returns to retard, now have to up idle to run at full retard. First time it revs again it's stuck at full advance plus high idle setting. Cycle repeats.

I had not considered this and will try to look into it tonight. I need to pick up a timing light from my dads. Thanks for the tip.

And replace both of your carb cables. Likely they’re rusted up inside preventing the cable to move freely through the sheath. But you should also check the minute space at the throttle housing to the brake perch. You want about a credit cards worth of gap.

It may come down to this, however, when i pulled the carbs, I also removed the cables, and clutch cable, and did the old baggie around one end and ran chain/cable lube threw them. They are clean and operate smoothly now, with no large cracks or spurs anywhere I can find. Thanks for the tip!

And dont operate the choke backwards.

That's gotten me quite a few times, but after rebuilding these, and noticing the choke lever even has an arrow, I feel pretty safe hahaha. Thanks for the tip

As well as all your other problems, timing advance being sticky can make things worse as well, check for loose springs. (wont retard until under 1000, back off idle to get lower than 1000, advance returns to retard, now have to up idle to run at full retard. First time it revs again it's stuck at full advance plus high idle setting. Cycle repeats.

I agree with checking your timing advance, I had a similar problem when I first got my bike and after cleaning up the advancing plate she purred like a kitten.

Two points for this one, I'll see what I can find out tonight and keep everyone appraised.


Thank you all for the quick and helpful reply's. We are very grateful.

[RAFster122s]

Sorry I thought Sudco carried the real Keihin jets.
See if other recommend other sources but Jetsrus is a good company too. I have seen where others have used them.

The advancer is a real contender for causing this as well... Pick low hanging fruit that you can clean or adjust or test without spending money to eliminate potential issues or causes.
Servicing the advancer will insure it is working properly and you are getting the correct timing advance. Adjusting the dwell and setting your timing with a timing light is good practice (practice as in best method...not practice like playing an instrument to get better) as well.

[BRG-BIRD]

I have a minor assortment of jets, not sure if 40’s are in there. Let me know if you need anything as they can be dropped in an envelope easily.

[calj737]

I would not worry one bit about the 38 vs 40 for your pilot jets. Stands to reason that due to emissions changes in '76 the smaller jet would be utilized to produce a more lean exhaust.

Your bike, like all small displacement 4s needs to be revved way up the band to produce any power. And I mean well above 6,000rpms. you'll constantly be in the Main Jet functional area of the carbs while riding.

Jetsrus has true Keihin brass. Order from there if you opt for new jets or needles. Sirius and Sudco sell Keyster products.

Some helpful images for your tuning benefit.

[Deltarider]

I've seen these schemes come by multiple times. The experience I have with my bike, a CB500 K2 [ED] ('76), in particular with the pilot airscrew and jet, is more reflected in the pic below however. Also I have compiled a scheme that I use.

[Azaswas]

Sorry I thought Sudco carried the real Keihin jets.
See if other recommend other sources but Jetsrus is a good company too. I have seen where others have used them.

The advancer is a real contender for causing this as well... Pick low hanging fruit that you can clean or adjust or test without spending money to eliminate potential issues or causes.
Servicing the advancer will insure it is working properly and you are getting the correct timing advance. Adjusting the dwell and setting your timing with a timing light is good practice (practice as in best method...not practice like playing an instrument to get better) as well.

No problem at all, and again thank you for your help. I'm not very savy with points/condition ignition systems. I've done a few SBC and old ford Y-blocks, but followed the manual and had a friend to help as well. On this bike, it looks like 1-4, 2-3 have their own, but how does the advancer work, and what should I do to "service" It? I don't see weights, springs except those on the points.

I did grab my timing light from my parents house, It was probably last used in 2010 on a sbc, which is the only other time I've used one!

Thank you, Carl and Tuyen.

I have a minor assortment of jets, not sure if 40’s are in there. Let me know if you need anything as they can be dropped in an envelope easily.

I'm definitely interested in the 38's and 40's If you have a set of each I would happily purchase them from you! Not sure, but i guess DM me on here?

I would not worry one bit about the 38 vs 40 for your pilot jets. Stands to reason that due to emissions changes in '76 the smaller jet would be utilized to produce a more lean exhaust.

Your bike, like all small displacement 4s needs to be revved way up the band to produce any power. And I mean well above 6,000rpms. you'll constantly be in the Main Jet functional area of the carbs while riding.

Jetsrus has true Keihin brass. Order from there if you opt for new jets or needles. Sirius and Sudco sell Keyster products.

Some helpful images for your tuning benefit.

Thank you so much, I'm sure these will be a great help!

I've seen these schemes come by multiple times. The experience I have with my bike, a CB500 K2 [ED] ('76), in particular with the pilot airscrew and jet, is more reflected in the pic below however. Also I have compiled a scheme that I use.

Interesting, I've just used this to match my 087A carbs and double check what I had was correct! Thank you again.



Here is what the setup looks like when I pulled off the cover. I checked in one of the repair manuals, that the gap should be about .3mm, and it seems perfect for that. It is is a little dirty, but doesn't look bad at all. The points also felt like they had plenty of life on the springs.

I noticed that in pictures, or online, the entire assembly seems to be centered with the 3 philips head screws, whereas mine is completely to the left. That doesn't  seem normal?  I'm just not sure how to proceed.

Sorry for the late response, we got caught up looking into other projects. Thank you all for your continual  feedback. I've attached some photos for y'all to check out, let me know if there is anything obvious, or what I should be looking for.

[Deltarider]

Have you checked for air leaks by spraying some brake cleaner near the rubber boots (carbs to engine) and where the O-rings sit between the manifolds and the head?

[RAFster122s]

The advancer mechanism is behind the points plate. The service manual/shop manual can be downloaded and it has removal covered...
The center nut on the points side can be deflected if you wrench on it too hard and this can introduce a wobble in the shaft which impacts the points and advancer.
The spark plugs need to be removed if you use it to rotate the motor.
If the shaft is bent you normally can gently tap it back into near true with some work with a small hammer and dial gauge to guide your work.

The nut on the rotor can be used to turn the bike over...or some have the bike in gear and use the rear tire to rotate it through...

[Deltarider]

Actually you can use that 23 mm for cranking - at least on a CB500/550 - provided you use a T-handle. I never had to remove the plugs.
But I'd start with checking for airleaks. Spray some brakecleaner and when the rpm changes, voilà.

[Spanner 1]

RAF +1 ! I would never turn the crank by that 23mm 'nut' on the end of the points cam with the plugs in, asking for trouble IMO. If the skinny points cam shaft gets bent then one set of points will be impossible to set correctly. Remove the plugs or do what I do and that is 'jab' the kick starter with my left hand in small increments ( plugs in ) to move the points cam while observing the timing marks,  works fine. Are you setting the points gap with the points cam in the correct position ? Here's how. Turn the main points plate to 1/2 way in its travel. Snug up the 3 screws. Turn the sub plate ( 2-3 points ) plate to 1/2 way in its slots, snug the 2 screws. Now rotate the crank until the 1-4 'F' mark appears at the index mark in the 'window', now rotate the crank another 90 deg ( 1/4 turn ) clockwise past the 'F' mark. Stop there. This is where the points cam is at it's max lift. Now set the points gap to 14 thou. and tighten the points screw. Repeat the process for the 2-3 points at 90 deg. past it's 'F 'mark. Now set the timing by turning the main plate for 1-4 points so as the points open @ the 'F' mark. Need a meter or test light for this part. Tighten the 3 main plate screws when done . Then turn sub plate ( 2-3 ) to achieve points opening at 2-3 'F' mark. Tighten screws, done !

[Azaswas]

Have you checked for air leaks by spraying some brake cleaner near the rubber boots (carbs to engine) and where the O-rings sit between the manifolds and the head?

Hey, I had originally, and I'm not sure if this is AFTER the third time removing/installing the carbs, but today, I THINK i may have found an air leak, although vague. I did replace those o-rings you mentioned yesterday and didn't notice a difference, although the ones that were there were almost completely flat. I don't think they were ever changed before. Thank you so much for your response.

The advancer mechanism is behind the points plate. The service manual/shop manual can be downloaded and it has removal covered...
The center nut on the points side can be deflected if you wrench on it too hard and this can introduce a wobble in the shaft which impacts the points and advancer.
The spark plugs need to be removed if you use it to rotate the motor.
If the shaft is bent you normally can gently tap it back into near true with some work with a small hammer and dial gauge to guide your work.

The nut on the rotor can be used to turn the bike over...or some have the bike in gear and use the rear tire to rotate it through...

Today I finally got some time to take a look at the timing, and although it was slightly off, after adjusting both plates, there is a noticeable difference, it wants to stay idling for longer, but this still hasn't fixed the issue. I did NOT get it down to the advancer, simply because I ran out of time. But I will try and get to this asap and get back to the thread. Thank you for your response!

Actually you can use that 23 mm for cranking - at least on a CB500/550 - provided you use a T-handle. I never had to remove the plugs.
But I'd start with checking for airleaks. Spray some brakecleaner and when the rpm changes, voilà.

I didn't know this! I havent gotten to check to see if i did any damage, however, i was gentle, and only using a small 1/2 drive...plus im guessing that I'm not on the top-end of the compression spectrum xD     Thank you for your response.

RAF +1 ! I would never turn the crank by that 23mm 'nut' on the end of the points cam with the plugs in, asking for trouble IMO. If the skinny points cam shaft gets bent then one set of points will be impossible to set correctly. Remove the plugs or do what I do and that is 'jab' the kick starter with my left hand in small increments ( plugs in ) to move the points cam while observing the timing marks,  works fine. Are you setting the points gap with the points cam in the correct position ? Here's how. Turn the main points plate to 1/2 way in its travel. Snug up the 3 screws. Turn the sub plate ( 2-3 points ) plate to 1/2 way in its slots, snug the 2 screws. Now rotate the crank until the 1-4 'F' mark appears at the index mark in the 'window', now rotate the crank another 90 deg ( 1/4 turn ) clockwise past the 'F' mark. Stop there. This is where the points cam is at it's max lift. Now set the points gap to 14 thou. and tighten the points screw. Repeat the process for the 2-3 points at 90 deg. past it's 'F 'mark. Now set the timing by turning the main plate for 1-4 points so as the points open @ the 'F' mark. Need a meter or test light for this part. Tighten the 3 main plate screws when done . Then turn sub plate ( 2-3 ) to achieve points opening at 2-3 'F' mark. Tighten screws, done !

Noted! I used ya'lls suggested "jabbing" technique and it worked great! I managed to adjust the timing and as I mentioned above it made a difference, but nothing substantial. I believe I did exactly as you described. I used the combined input of your post, youtube, Clymers and Haynes repair manuals I scored for a few bucks at a garage sale to get this done Thanks your your response.




To update ya'll yesterday I managed to find some time to wrench on this again, and I first started out by taking the carbs off and replacing the jets with my stock 38's. This is no easy task because of those stupid ROUND float bowl O-rings...Thank god for transgel. after this I removed the intake's and replaced the o-rings courtesy of my local Honda power-sports dealer (they had them in stock) and cleaned everything up a bit. I figured while I had the gas tank off I would go ahead and change the plugs, as I had new NGK ones from a kit i ordered awhile back. When I was removing the plugs (if anyone was wondering the spark-plug removal tool from a 1987 Kawasaki ZG1000 also works perfectly for this bike) I noticed that number 3 spark plug wire boot was an aftermarket NGK one that not only DID NOT FIT, but was not even really connected. Again, like the carbs It's a miracle this thing was firing on all four when i got it. After some extremely makeshift fabrication I managed to make something work out of some lawn mower parts whilst waiting for the Honda parts to arrive. After getting everything back together, I started her up and noticed almost no difference. That to me is interested, the aftermarket-wildly different 38's, and the stock K ones that came with the bike, offer zero change when swapped.


Thank you all for your continued support and reading. Will try to keep getting new information and keep posting. , but I don't get enough time to post every day so I apologize for the sporadic updates.

[Scott S]

 Your title says the bike WON'T idle but, correct me if I'm wrong, you're having a problem with it idling too high after revving. Right?

 Since you've checked the carbs, jets, O-rings and vacuum leaks, take a look at the advance mechanism. You need to remove the points plate and the mechanical advancer. Clean the mechanism where the cam slides over the shaft. Pay attention to it's orientation; there's a tiny dot on it. Clean and lightly lube the shaft with some light oil. Trim the "hook" portion off the end of the springs and then bend the spring over to create a new hook. This strengthens up the weak springs.

 And have you changed grips recently? Is the rubber end of the grip grabbing on the end of the handle bar or on the RH switch housing?

[Scott S]

 One way to test if it's the advance and not jetting or an air leak: Next time it hangs, slowly release the clutch lever just into the friction zone. Does the idle drop back down to normal?

[Deltarider]

Actually this is the better picture of the CB500/550 advancer. It shows, framed in white, what part of the cam should face the hole after reassembly. Mind you, that dot or carf in the rim of the cam is very small!