Topic: Purchasing a second Honda, bike doesn't run when warm owner said.

[Vhonda]

I found a good deal on a CB550four, the previous owner said it was running but recently it stopped running after 15 minutes when the engine warms up. Here is his recollection of the history of this bike.

1. The bike was running for four years, decided to put in foam pod filters and had a third party change the jets(currently has 110 jets).
2. He said the bike was running fine re-jetting this year until 3 months ago, the bike would not idle or stay on after 15 minutes of riding.
3. There is no oil leaks motor, everything else works as should, bike is clean.
4. The bike started right up, cold start when I first saw the bike, 2 day later when I transported the bike home it had trouble staying idle. I suspected he fumbled with the air mixture screws, bike was running lean. I have been out of town and haven't been able to work on the bike.

A. This is my second vintage Honda, most issues I dealt with in my 1st bike were electrical and broken rubber and gasket around the carbs, resulting in high idle vacuum, and carb syncing. I still have charging/rectifier issues but that is for another day.

B. I am planning to change the jet back to stock on this new purchase and find an original airbox over the winter, in the meantime I want to get this bike running before summer is over. I have cafe racer mod already and would like to keep this one bone stock. (Does anyone have stock setup for sale I would be interested 1976 CB550)

Any insight will be helpful, I haven't wrench for the last 3 years and I just need buddy support.

[BenelliSEI]

I bought a cb750K3 with the same issue. The owner suggested it was “seizing up” when hot. As soon as it cooled down it would start right up, for another 15 minute run…..

Took me a few days to figure out the gas cap vent was plugged solid with rust and crap! Created enough vacuum in the tank it just ran out of fuel. Half a hour later, the float bowls would refill. Drilled it out and the bike is still running great, 11 years later.

[Vhonda]

Thanks for the tip! Your reply led me to narrow my search.

I found this old thread also after your reply. (http://forums.sohc4.net/index.php/topic,183639.0.html)

1. Gas cap vent
2. Loop in the gas line (Having a loop in the gas line and perhaps the clear fuel line is not heat resistant, poor quality)
3. Dirty Fuel, clean petcock.

on another forum "THE STOCK DR650SE GAS CAP" the same issue bike stops running after warm-up. Turns out the rubber seal on the inner gas cap swells up during the ride from heat and then blocks the gas vent.

In another post, the builder painted his tank and painted over the gas vent hole.

A search on youtube yields a bad spark plug coil that overheats at optimal temperatures.

Might as well change the ignition coils, boots, ignition contacts, and condensers.

Did I miss anything?

[CycleRanger]

Thanks for the tip! Your reply led me to narrow my search.
A search on youtube yields a bad spark plug coil that overheats at optimal temperatures.

Yep, after ensuring good fuel delivery I would look toward the electrical.

[HondaMan]

Might as well change the ignition coils, boots, ignition contacts, and condensers.

About this: the points won't cause this, and the old points are better than most you can find today. The condensors today are a nightmare, and yours are still good, I'd bet $5 on each one, now. Re-use at least the condensors if you replace the points.

A dying coil on this bike CAN cause 2 cylinders to stop firing when hot: the best test for this could be to run the engine up hot until it quits, then lay a spare sparkplug against the cylinders and plugged into the sparkplug wire(s) and crank it to see if it sparks - or not. I have seen both the CB500 and the CB550 'lose' a coil like that, where it works cold but not hot. The space around the coils is pretty tight on this bike, and in-town riding heats the coils a lot for lack of airflow over them.

The fuel line: it should run as horizontally as possible between the petcock and the carbs, and never, never, never go down, and then back up. That won't work.

BTW: some excellent coils are the Sakura from PartsNmore.com, #17-6823. If they don't show up in the CB550 section, look in the CB750K section. Same parts.

[Ozzybud]

Might as well change the ignition coils, boots, ignition contacts, and condensers.

About this: the points won't cause this, and the old points are better than most you can find today. The condensors today are a nightmare, and yours are still good, I'd bet $5 on each one, now. Re-use at least the condensors if you replace the points.

A dying coil on this bike CAN cause 2 cylinders to stop firing when hot: the best test for this could be to run the engine up hot until it quits, then lay a spare sparkplug against the cylinders and plugged into the sparkplug wire(s) and crank it to see if it sparks - or not. I have seen both the CB500 and the CB550 'lose' a coil like that, where it works cold but not hot. The space around the coils is pretty tight on this bike, and in-town riding heats the coils a lot for lack of airflow over them.

The fuel line: it should run as horizontally as possible between the petcock and the carbs, and never, never, never go down, and then back up. That won't work.

BTW: some excellent coils are the Sakura from PartsNmore.com, #17-6823. If they don't show up in the CB550 section, look in the CB750K section. Same parts.

+1 on a bad coil. I have had this happen to me more than once. 15 min and they stop working!

[newday777]

I found a good deal on a CB550four, the previous owner said it was running but recently it stopped running after 15 minutes when the engine warms up. Here is his recollection of the history of this bike.

1. The bike was running for four years, decided to put in foam pod filters and had a third party change the jets(currently has 110 jets).
2. He said the bike was running fine re-jetting this year until 3 months ago, the bike would not idle or stay on after 15 minutes of riding.
3. There is no oil leaks motor, everything else works as should, bike is clean.
4. The bike started right up, cold start when I first saw the bike, 2 day later when I transported the bike home it had trouble staying idle. I suspected he fumbled with the air mixture screws, bike was running lean. I have been out of town and haven't been able to work on the bike.

A. This is my second vintage Honda, most issues I dealt with in my 1st bike were electrical and broken rubber and gasket around the carbs, resulting in high idle vacuum, and carb syncing. I still have charging/rectifier issues but that is for another day.

B. I am planning to change the jet back to stock on this new purchase and find an original airbox over the winter, in the meantime I want to get this bike running before summer is over. I have cafe racer mod already and would like to keep this one bone stock. (Does anyone have stock setup for sale I would be interested 1976 CB550)

Any insight will be helpful, I haven't wrench for the last 3 years and I just need buddy support.

Welcome aboard the forum and the quest of returning your CB550 back to stock. I won't inject any more on the carburation changes as I don't know the 550 carbs intimately.
In reading through your search for the sidecovers, my parts manager mind noticed you use of CB550F and CB550Four here and in the sidecover post, then seeing your pictures in this link, that you need to change your designation of what model you have, so you get the correct information and parts when asking as you have a 76 CB550K according to your picture. The CB550F is the Supersport model, not the CB550Four as the sidecover emblems say, so be mindful of that when you get looking for parts, so you can get the correct parts as there are changes in the sidecovers and also pieces of the airbox(if I remember correctly) Shortening Four to F is a bad practice that can lead to misinformation.
Sorry for the rant.
I hope you project goes well as the 550 is a great bike when running correctly. Is that picture your bike or just a download of a stock CB550K?

Post back a reply of how you get along on the running once you make the changes in your jetting here(update this thread with replies rather than starting a new thread, it'll help keep confusion to a minimum for all to have all the information given in one place rather than having to search your multiple threads as time goes on)
I hope this is helpful and not a deturant for you.

Did you hit the notify button at the bottom of your threads so you get an email when someone replies? It isn't an automatic thing in this forum as in others have that I'm part of.

[Vhonda]

newday777 thank you for the reply and information.

The bike in my avatar is the actual new bike I just purchased with the Carb issues, which as you stated is a CB550k. I am looking to purchase another 76 model CB550 Super Sport model (photo below-blue), if I can get this one running first.

I also own another CB500 73 model

[Vhonda]

I can see air bubbles traveling through my fuel line upwards towards the tank. Is this normal?

Can these air bubbles be an issue if the vent in my gas tank is not working properly? I noticed my gas cap was difficult to open, the pressure I applied to the lever was not enough to release the gas cap. It took many tries.

The bike idled fine with the choke closed. when I opened the choke the motor died. I assume the air screw mixture, choke and Idle knob needs to be reworked.

I rode the bike around for 10 minutes and parked it in neutral and let it idled for 10 minutes before I shut it off for the day.

[jonda500]

To open the gas cap you need to push down on the cap, then operate the lever (whilst pushing down on the cap).
The air bubbles are nothing to worry about. Not running without the choke closed points clearly to a carby problem.
John

[Vhonda]

Jonda: thank you, I did push down on the cap and then apply pressure to the lever.

The choke was in the closed position, the bike running, and when I opened the choke the motor died.

My understanding is that opening the choke created a lean condition, causing the motor to shut off.

I am going to pull the pilot jet screws and clean them. I don't have any problem when the bike is on the road, just idle issues.

[grcamna2]

Following

[Deltarider]

Replace asap the fuellines by ones that have exactly the right dimensions: 17 and 28cm length and an ID of 5,5mm, routed as shown in the pic. Use that clamp! Your fuelline runs too close to the hot engine. If your bike happens to have the old bowltype petcock the CB550(K0) had, length should be 18 and 30cm resp. OEM for your model however was this petcock which requires the 17 and 28 cm lines: https://www.cmsnl.com/honda-cb500k2-general-export_model50441/cockfuel-cb550f_16950374671// Don't be tempted to have them even one cm longer! This to avoid kinking.
Abstain from inline fuel filters! Fuel supply is often impeded, when fuel routing is not exactly as designed by Honda. I have seen enough problems with lines going down and up not to mention inline fuel filters! Have it standard!

[Deltarider]

[...] I am going to pull the pilot jet screws and clean them. I don't have any problem when the bike is on the road, just idle issues.

What you could try first, is remove the airscrews in the sides of the carbs, then spray carb cleaner (use a straw)  in the now open holes and hopefully the carb cleaner will find its way towards the slow jets. Before you remove the airscrews, turn them in - gently! - and take note at what position they were, so you will be able to set them back where they were, after you completed the operation. I haven't tried this myself yet*, but imo it's worth trying and saves you the trouble of removing the floatbowls. It's not really extra work, when you were prepared to do this anyway. Please report back if this simple method has worked.
*I forgot to mention what I have done to come to this suggestion. Some years ago with the rack in situ, I had the bowls removed and the airscrews. Out of curiousity I have then sprayed carbcleaner (via its straw) in the holes where the airscrews sat and was surprised to see the carbcleaner immediately pouring down through the slow jets, indicating all four slow jets were open. Again, imo it's worth trying. Please report back. When succesful you have rendered this forum a service.
BTW, in the past I have been succesful in getting the slow jets out, by just removing the bowls, so without pulling the complete rack. I do all my carb maintenance without pulling the rack. Replacing the 16 crossheads by allen decades ago, has helped me a lot.

[HondaMan]

BTW, in the past I have been succesful in getting the slow jets out, by just removing the bowls, so without pulling the complete rack. I do all my carb maintenance without pulling the rack. Replacing the 16 crossheads by allen decades ago, has helped me a lot.

Wow! You have nimble fingers!

[Deltarider]

Well, to be honest, once you have had these carbs on the table a couple of times, you become familiar with what's inside. I can do it blindfolded by now. To unscrew the slow jets, use a small screwdriver that you insert into the slot sideways, to just break the jet loose. From there your fingers can unscrew it further.
What you could also do prior to eventual removing the bowls is have the engine run at idle or close to idle. Then turn the airscrew of carb#1 in completely, wait 10 seconds and then out three turns and wait another 10 seconds. A change in rpm - can be minor - indicates that particular idle circuit is still functional. Repeat for the other carbs, one at the time. When all idle circuits are functional, usually a dose of some fuel system cleaner is all what it takes. Also gasoline itself cleans pretty well. This goes for these oldstyle carbs. The PD carbs is a different story... 

[Vhonda]

Well, to be honest, once you have had these carbs on the table a couple of times, you become familiar with what's inside. I can do it blindfolded by now. To unscrew the slow jets, use a small screwdriver that you insert into the slot sideways, to just break the jet loose. From there your fingers can unscrew it further.
What you could also do prior to eventual removing the bowls is have the engine run at idle or close to idle. Then turn the airscrew of carb#1 in completely, wait 10 seconds and then out three turns and wait another 10 seconds. A change in rpm - can be minor - indicates that particular idle circuit is still functional. Repeat for the other carbs, one at the time. When all idle circuits are functional, usually a dose of some fuel system cleaner is all what it takes. Also gasoline itself cleans pretty well. This goes for these oldstyle carbs. The PD carbs is a different story... 

Deltarider, thank you for your knowledge and replies. I am going to do what you suggested on Monday and post back. Those rubber carb boots look like they have already started cracking.

Great suggestion on replacing the phillips with allen wrench ones for ease of access.

I also plan to replace the filter that took place of the crankcase breather tube, smoke coming from the center of the bike is a bad idea overall.

[grcamna2]

Well, to be honest, once you have had these carbs on the table a couple of times, you become familiar with what's inside. I can do it blindfolded by now. To unscrew the slow jets, use a small screwdriver that you insert into the slot sideways, to just break the jet loose. From there your fingers can unscrew it further.
What you could also do prior to eventual removing the bowls is have the engine run at idle or close to idle. Then turn the airscrew of carb#1 in completely, wait 10 seconds and then out three turns and wait another 10 seconds. A change in rpm - can be minor - indicates that particular idle circuit is still functional. Repeat for the other carbs, one at the time. When all idle circuits are functional, usually a dose of some fuel system cleaner is all what it takes. Also gasoline itself cleans pretty well. This goes for these oldstyle carbs. The PD carbs is a different story... 

Deltarider, thank you for your knowledge and replies. I am going to do what you suggested on Monday and post back. Those rubber carb boots look like they have already started cracking.

Great suggestion on replacing the phillips with allen wrench ones for ease of access.

I also plan to replace the filter that took place of the crankcase breather tube, smoke coming from the center of the bike is a bad idea overall.

Oh yes,clean or Replace that PVC filter and monitor it to allow it to breathe well.

[Deltarider]

Some CB550 owners had issues with that breather thing underneath the airfilter element. A remedy often practised, was to have the breather tube vent into the open and seal the holes in the airfilter and its case. Some turned to the CB500 airfilter element that didn't have the opening in the bottom. 

[Vhonda]

REPORTING BACK:

This bike always starts on the first try, choke closed.

Notice choke lever screws were getting caught up on the filter clamps, re-adjust.

Clean air mixture screw as suggested. The screws where 3.5 turns out, sprayed carb cleaner down and air clean the needle screw. set to 1.5 turns, not enough air, went to 2 turns stabilized.

The fuel tank was at 1/10th full so added seafoam to 1 to 3 parts fuel. when I have time can soak float bowls overnight and clean them in the morning and then refuel. I would like to mix 50/50 fuel and seafoam in a separate fuel bottle and let it run out when I have more time.

OK SO I THINK I FOUND THE PROBLEM: The fuel line is too long and was up against the bike, when the bike stalled after riding for 10 minutes and was warmed up, I went to look at the fuel line and the fuel had a huge air bubble and the fuel was no longer flowing to the float bowls. The fuel line had extensive heat and was very hot. I think this explains the bike stalling after 15 minutes of riding and then waiting for the bike to cool down.

Also the battery was low, got a charger for the battery and shortened the fuel line and re-installed. Bike started back up no problem, rode around the block.

Enough for today. Will ride it around tomorrow to see if this holds up.

Thank you Deltarider!

[Vhonda]

DAY 2 REPORTING BACK:

So I had seafoam left over from yesterday in the float bowls and the bike did not start right away. I pulled the drain screws and emptied the bowls. I also noticed the 2nd fuel line did not have good flow so I clipped off half an inch. Added fresh fuel and the bike started right up.

BATTERY: I charged the battery overnight and it said it was fully charged. I usually check the strength of the battery by testing the horn. After only a few ignition switch failed start the battery went low. I suspect this battery is older and has sat over from the winter months. I will be getting a new battery. Other than that the bike kickstart works as it should. My other CB500 has no electric ignition start circuit so I am use to kick-starting only.

I rode the bike for well over 15 minutes parked and let it idle with no issues. The choke is always closed and I don't need it to start this bike or keep it at idle. My air mixture screws are turned out at 1 3/4 turn from seated.

I did notice the kickstand was rubbing on the asphalt when making left-hand turn, guess I need to find a different kick stand option. For now, the center stand feels useless because I don't know how to use it, maybe I am just too old and don't have enough strength to pull the bike backward.

Probably will end up keeping these handlebars as they are comfortable, just had to adjust the position.

[Vhonda]

DAY3:

New Battery, adjusted air mixture screw from 2 turns to 1 3/4 turns, flushed all the old fuel out of carbs and tank. Runs 100% better, stable 1,200 rpm idle and no muffler backfires. Kick Start only, I don't use the electronic starter, a good measure of how tuned the bike is.

These carbs are sensitive so for the future I recommend fresh fuel. Pull mixture screws and spray carb cleaner as suggested by Deltarider, replace fuel lines, air-blow pet cock, and anything the fuel touches stopping only at the engine.  Even better if you can get to the idle and pilot jet and give them a good cleaning.

Notice rear brake lever is hitting the muffler when engaged, made some adjustments.

Had 3 conversations at the refuel station about the bike, a good day.

IN CONCLUSION: Old fuel, clogged idle jets, air mixture screw settings, reset idle 1/2 screw/knob, cut and refit fuel line to correct length, run seafoam.

FUN FACT: "The 1976 model was offered in a single color, Candy Garnet Brown."

[Vhonda]

DAY4: The bike started and the float bowl closest to the clutch side started to overflow while the bike was running. Unscrew the float bowl drain screw, empty the float bowl of fuel, compressor air through the drain plug and also the over-flow needle. That did the job, rode around the block, done for the day.

These carbs are sensitive and this gas tank needs cleaning, along with all the fuel lines and petcock.

[CycleRanger]

DAY 2 REPORTING BACK:
I did notice the kickstand was rubbing on the asphalt when making left-hand turn, guess I need to find a different kick stand option. For now, the center stand feels useless because I don't know how to use it, maybe I am just too old and don't have enough strength to pull the bike backward.

Regarding using the center stand. There's a trick to it.
You use your foot to to push down and lever the bike up.
Here's a short video demonstrating the technique.
Not a Honda obviously but the method is the same.

[Little_Phil]

Looks like your bike has setbacks on the rear suspension. This lowers the seat height and makes it easier for us shorties. But also makes getting on the main stand much harder. The main stand on the 500s and early 550s is bad at the best of times as the angle on the foot lever is poor. It's much better on the Fs and the K3s.