Topic: Non Running 74 CB550 in KC

[SlapShooter90]

Hi All,

I know nothing about motorcycles but have always wanted to work on one and love the vintage CBs. I picked up my first bike, a running (at the time) but dirty 74 cb550K about a month ago. I worked through title paperwork and finally got the title two weeks ago. I charged the battery which seems reasonably new but the PO described as "cheap and in need of a good charge" and tried to start the bike but it wouldn't run. The motor cranked with both the electric start and the kick start.

After browsing the forums here, I charged the battery again, changed the oil and oil filter, put in new spark plugs. Tried to fire it up again and got cranks but it still wouldn't start. This week I emptied the old gas, filled with fresh ethanol free gas, cleaned the petcock bowl, and replaced the over-sized fuel lines with 5.5mm ID lines that are (I think) properly routed. Today after changing the fuel lines and charging the battery for nearly 5 days, the electric start wont crank, I only get a disappointing click. The kick starter still turns the motor.

Got any ideas what to check? I'm thinking of picking up a new battery but not sure what else to look at at this point.

Also, when I turn on the ignition the oil light doesn't illuminate but the neutral light does. I pulled out the instrument lights and the multimeter reads no voltage in the oil light socket, so I am assuming there is a short somewhere. Electrical is magic to me, where should I start to address the short?

Any suggestions are appreciated and I appreciate all your help!

[b52bombardier1]

Carbs are probably dirty. Try just a little starting fluid, one time. That will tell you if it's carbs. Any more starting fluid than just a little can damage the cylinder oil film. Don't use it as a crutch.

Does it have spark at the plugs? Have you checked compression?

Rick

Sent from my SAMSUNG-SM-N900A using Tapatalk

[calj737]

If you only get a "click" now after charging the battery, I would suspect either the key switch or the KILL/RUN switch is faulty.

Turn the key to ON, RUN switch set, push the START button. What happens to the headlight?

Under the left side panel, you will find the fuse block, starter solenoid, and the balance of the charging components. Locate the solenoid (it has 2 posts with a large gauge wire on each, and 2 thinner gauge wires ((one should be Yellow/Red striped)). With the bike in Neutral, use a screwdriver and jump the solenoid between the 2 posts. This should spin the starter. If it does, time to troubleshoot your KILL switch or Key switch.

As for "cranking but no fire", probably the carbs need a really good, thorough cleaning. You can remove them and send them to a member here, Harisuluv, and he will rebuild them to factory perfect condition for a very reasonable fee. Do NOT use aftermarket rebuild kits except for the o-rings and gaskets. The stock brass inside your carb is best, and easily cleaned up.

[SlapShooter90]

Thank you for the responses!

b52: It does have compression, but it's low. All four cylinders are between 120 and 125. I checked for spark when I first changed the plugs and they all sparked but I haven't checked since. When the electric start was still turning, I used a shot of starting fluid and it fired up for a few seconds and then died (fuel lines were disconnected).

calj: Thanks for the tips! I will look into these when I have time and let you know what I find out.

Should I be concerned about the oil light short? Or worry about that after taking care of the engine?

Thanks for your help!

[calj737]

Should I be concerned about the oil light short? Or worry about that after taking care of the engine?

The OIL light receives 12v on a BLACK wire, shared by NEUTRAL light. There's a BLUE/RED stripe wire coming from under the left side engine cover (behind the shift pedal cover) where it hits the oil pressure sensor. That runs along to the electrical panel, then up to your instrument cluster in the main harness. But the BLUE/RED is the "ground" side, so if you're not seeing 12v, you're missing the BLACK connection somewhere up there.

And just for reference: on your bike, BLACK is switched 12v, GREEN is ground.

[SlapShooter90]

Ok, I finally had some time to look back into the bike. While I was gone my new battery arrived and that seems to have done the trick. Slapped it in and the starter turned right over.

I was able to get the engine to run by squeezing the clutch lever and using the electric start. As soon as I try to let it idle though, it dies. What do you suggest I look into for the idling issue? Is that due to dirty carbs?

Also, PO had cleaned the carbs so the air box and rubber connectors are currently removed and there is no air filter/element. From what I've read that may be contributing to this issue. What do you think?

[calj737]

Are you operating the choke correctly? You'd be surprised how many new owners close it when they think it's open. Look into the carbs since the air box is off, and confirm it's open. Don't let the bike idle with it closed; it will die due to too rich a fuel mixture.

[SlapShooter90]

That's a good point, I honestly don't know if I am working it correctly. When I start the bike should it be fully open?I currently have the lever parallel to the ground when starting. When the choke is "open" should the valves (improper terminology I'm assuming, sorry) to where the airbox should be connected open up?

My starting procedure is currently:
1.Open petcock
2. Turn on ignition
3. Hit starter and use a little throttle

At that point I have to hold the throttle or the bike will die. I'm assuming the choke should be open at that point?

Thanks for putting up with my stupid questions, you've been a tremendous help!

[calj737]

Look into the carbs. You'll see the "flaps" move when you adjust the choke lever. "Choke" on is the flaps closed to enrich the fuel during start up. Open )normal riding position" the flaps should be parallel to the ground to allow air flow to maximum as you are adding fuel with the throttle.

The lever is oriented as the flaps are: parallel lever, parallel flaps. Vertical lever closed flaps.

Your bike could also have "other" carb issues, but get this straightened out first to rule out "new owner issues" from tuning requirements.   

[Stev-o]

Slapshooter...welcome to SOHC4.  I also have a '74 550, here is my starting procedure for a cold start:

1. Turn on fuel
2. Turn on full choke
3. Turn on ignition
4. Push start button, once motor fires, give a little throttle and reduce choke to half.
5. Hold throttle for 1-2 min at 1500 RPM idle or til warm.

These old bikes can be particular the way they like to be started. Once you know, no big deal.  Once bike is fully warmed up, set idle to approx 1200 RPM. Good luck!

[surfrider74]

Have the same bike but its the 550Four.
Boss Maroon/Black-wish i had it in the Sunburst Orange.

Anyway mine had gummed up carbs when i bought it-needle and seats in all carbs gunked up from months of sitting in California Ethanol gas. Rebuilt all four carbs and synched and had to replace non venting gas cap that was causing vapor lock and starving it for fuel. One of my coils was bad and would open when hot.
Id say check your carbs next and look into at least completely cleaning them.

[SlapShooter90]

Thanks for clearing that up Cal. By dumb luck I was doing it correctly and starting the engine with the choke on full (flaps closed).

Stev-o - I tried this method but as soon as I move the choke off full, the engine dies.

Another observation that I made is that is somewhat difficult to maintain constant RPMs with the throttle below 2000. If I try to hold it steady below roughly 1800 the RPMs crash fast and I have to add more throttle. I will try and take a video later. What would you guys recommend I check next?

[Stev-o]

Confirm you have OEM jets and if so, clean thoroughly. 

[calj737]

There is little dispute from your posts that the Previous Owner did NOT clean the carbs properly. Cleaning the fuel bowls matters very little as a maintenance service because the fuel jets are absolutely critical.

You want if at all possible to use the stock jets (Keihin brand) and the correct size. You must be certain the MAIN and Idle jet, AND the EMULSION tube are completely clean. This will necessitate the removal of the carb rack from the bike. Don't need to separate the bodies from the rack, just the rack to access the tops and internals of the carbs.

Look at carb #4 (your far right seated). On the outside of it is a model # stamped in the flange. What is it? This is your guide for jet sizes, needle clip position, etc.

You'll be adjusting the slides of the carbs after you clean them via a method called "bench synching". This will help your carbs equalize the vacuum drawn and stabilize your idle. You can fine tune that with a vacuum gauge once the bike is running and the carbs are reinstalled.

Also, while off the bike, you can use the Clear Tube method to accurately set the fuel level float height. (Picture attached).

I know this sounds like a lot, but I assure you it will shorten your diagnosis, resolve 90% of your problems with the bike starting and running, and survive the next several years if you take decent care of the fuel system. Plus, its not really that hard (just sounds involved and intimidating). 

[SlapShooter90]

Ok, I will take the carbs off this weekend and dig in to them if I can find the time. The carbs are 022A which is stock for the model year. The bike has a 4 into 2 exhaust which obviously isn't stock, but I'm not sure what brand it is. Also the PO cut out the baffles "because it was pretty screwed up in there". How will these differences affect the jets?

Also, I was going to do this eventually but if I'm removing the tank to get the carbs off I figure I met as well do it now. I want to use electrolysis to clean the tank as it is heavily rusted. Do I need to remove the petcock or will it be ok if I leave it on? Would you suggest coating the tank after (if it cleans it)?