Topic: CB550K Hesitates and stalls out during 10 minute highway rides

[cbnewb]

Greetings all,

First post for me.  I tend to be wordy, so my apologies in advance.

I picked up a basket case 1975 CB550K a couple weeks ago which was going to be parted out if it wasn't sold.  I couldn't bear to let that happen, especially with the stock exhaust headers still on the bike, so I shelled out a very low sum and trailered it home.

An initial walk-around showed the bike to be pretty haggard, but it still started and idled very smoothly and pulled hard even into the high RPM ranges without issue.  During a longer ride at highway speeds, however, the engine runs great for a short time, then stumbles, surges for a few seconds, then quits.  Starting it up again right away is possible, but the smooth idle is gone as is any semblance of power, and it will not idle on its own - the throttle must remained slightly tweaked for it to continue running.  I was able to limp it home.  After sitting for a short while, the bike starts and runs smoothly again.

The carbs had been recently cleaned according to the owner, but I did note the swamp growing inside the fuel tank.  I have an order for the full refurb kit from POR-15 arriving tomorrow, which was ironically ordered for a different CB I'm currently working on.  I believe I can make it stretch to cover both tanks.

I'm looking for opinions, or at least a confirmation on my read.  I believe the bike is experiencing fuel starvation issues due to the AMAZING amount of rust inside the tank.  I'm uncertain why anyone would go through the carbs at all and leave the tank in the condition it's in, but to me a lack of fuel makes sense.

I've checked out the points, they're in surprisingly good condition, though the did require small adjustments.  The bike is timed, the valves have been adjusted to specs.  The battery is new and the bike is putting out enough voltage to maintain the charge... possibly slightly too much of a charge as the bike is having some fuse issues which are a ways down on my list of things to address.

The only other thing I can think of are condensors, but I will begin with cleaning out the entire fuel system starting with the tank, and then working my way through the lines and into the carbs themselves.  Can anyone think of other possible causes?

This would be defined as a complete "snotter" by Carpy, but it still has a charm all its own, and there is some satisfaction in showing up at work on a bike with rusty ape-hanger bars and what appears to be a dull grey house paint covering all the normally painted surfaces.

I should mention I'm in the process of restoring a 1976 CB750F1 and just picked up non-running (now semi-running) 1975 CB550K which has an amazing patina on its "flake sunrise orange" paint.  I'm learning as I go, and figured 3 bikes would make me learn that much faster.     (I also have a 2002 harley I'm using as a daily driver, but it's far too boring and reliable nowadays)

Thanks for your thoughts and opinions,

CBNewb

[cbnewb]

My apologies, the bike in question is a 1975 CB550F Supersport.  I refer to them all by their first names, so I sometimes confuse the actual model numbers with others in the garage.  It does have the lovely flowing 4-into-1 exhaust headers, albeit slightly rusty.

[KCRSXTypeS]

My apologies, the bike in question is a 1975 CB550F Supersport.  I refer to them all by their first names, so I sometimes confuse the actual model numbers with others in the garage.  It does have the lovely flowing 4-into-1 exhaust headers, albeit slightly rusty.

I had the same problem.  I would say take care of the tank first but my problem ended up being the petcock.  I had bought a new one but for some reason it wasn't giving any fuel flow other than a drip.  My solution was to disassemble the petcock where I fount a bunch of rubbery gunk that looked like snot.  I cleaned it out, put it back on, and had full fuel flow.  Making sure everything is clean and in working order before buying parts is the direction I would go.

[Mdub]

If it runs for ten minutes and stops, it is most likely the fuel cap vent.
Good luvk,
Mike

[cbnewb]

Both sound pretty easy to check, especially the cap vent.  I risked life and limb this morning to show off its amazing coolness at work and ended up chitty-chitty-bang-banging my way into the parking lot.  I'll try to force the issue to repeat on the way home and see what I can hear when I pop the cap open.

KCRSX, you're on deck after that.   

Thank you both for your suggestions, I'll drop back in once I know more.

[KCRSXTypeS]

Both sound pretty easy to check, especially the cap vent.  I risked life and limb this morning to show off its amazing coolness at work and ended up chitty-chitty-bang-banging my way into the parking lot.  I'll try to force the issue to repeat on the way home and see what I can hear when I pop the cap open.

KCRSX, you're on deck after that.   

Thank you both for your suggestions, I'll drop back in once I know more.

Yea, If you are riding it and it starts to do that, the best way to check the vent is to just pop the cap open.  If the bike picks back up after a few seconds or if it dies but will start back up right away then it was the cap.  I blew some compressed air in mine and heard a pop but it never fixed the problem since it turned out it was the petcock but the cap vent is a good place to start too.

[bozo4onion]

Thanks for saving a 550F. IMO the best SOHC. I really would like a factory pipe. Pipe is over $1000 complete from Honda (they still make them). I hear they are kinda quiet. Your problem sounds tanky to me and I also currently have a petcock that only works on reserve so I think you are on the right track now. Here's mine, restored. Congrats on the new bike.

[cbnewb]

Now that's a pretty bike.  I believe the bike in question was originally that same orange color as well.  It would just appear that the paint roller couldn't spread the dutchboy paint into all the nooks and crannies around the gas cap, so there is some of the original paint still visible under the cover.

Yes, the bike is almost disturbingly quiet with the factory exhaust.  It's a very pleasant and mellow sound, entirely different from the CB750F1 and CB550K I've had running recently.  I feel almost bad about how little I paid for it though.  The muffler itself appears to be brand new and an OEM Honda part, which by itself is worth far more than I paid.

The longer I work on it, however, the less guilty I will feel.  This makes bike number 2 saved from the chop shop.  I'm lucky in that there isn't much I can do to make it look any worse.  Once I work out how to post a picture, I'll put one up here so that everyone can appreciate its awesomeness.

Thanks for the inspiration.  Just need to get from here, to there.  Easy Peesy! 

[cbnewb]

Attempting to post an image...

[KCRSXTypeS]

Attempting to post an image...

Thats a damn good looking bike except for the mini ape hangers lol

[cbnewb]

It's a good 20-footer.  The problems areas get a bit more visible when you take about 1 step closer. As with all 30+ year old bikes, it's the stuff you can't see that ends up blowing the budget.  That paint... LOL... oh my.  Looks like it was just rolled on over the top of the existing paint, then had sand added to make it all non-slip.

But it has both side covers in good condition, both fenders show very few blemishes, and those two things along with the complete headlight bucket assembly would have gone for far more money on Ebay.  I can completely understand why people part them out.

But not for this fella.

[bozo4onion]

Hey cbnewb, The Dutch Boy might polish up with a little Comet or Ajax . Seriously the seat looks good which is a good start. I found my original color under the tank door too. I think 75's only came in Sapphire Blue or Flake Sunrise Orange.

[cbnewb]

Wouldn't you know, I couldn't make it fail last night, though I was unable to get up to highway speeds and maintain it for any length of time due to traffic.  To further complicate matters I had stopped in the morning and dumped a small container of seafoam into the tank prior to posting here, so I'm unable to confirm that it's truly been addressed. 

We're due for storms for much of the rest of the week, but I'm fairly waterproof...

I checked the underside of the gas cap - it looks similar to photos I've seen of the titanic on the ocean floor.  Is it safe to assume the hole above the chain connection is the vent?  I'll need to get in there and grind off the barnacles in order to see any detail.  In a pinch, I have the cap from the 750F I can use.

I'll pull the 550F into dry dock tomorrow and see what I can discover.

Thanks again,

CBN

[cbnewb]

Oh, umm... hijacking my own post, but...

Bozo, can I ask where you tracked down the paint for your bike?  The 1975 550K I have sitting patiently in the garage has the original (now faded) factory "Flake Sunrise Orange" paint.  I really admire the heavy golden undertone to the paint, and the flakes are so very large.  I have yet to attempt a search online, but yours looks amazing, figured I'd let you do the work for me.   

Thanks much...

CBN

[Zaipai]

Yes I too would like to know where to get that flake paint. Also Great find on the 550!!

[cbnewb]

Here's "Lenny" (75 550K) waiting patiently in the wings.  This bike will be the subject of a whole lot of posts of it's own, but I figure it would be nice to see a "before" to compare with Bozo's very classy "after".

More on the possible fuel starvation after the storms subside.  Thanks again all.