Topic: '77 CB550K - Newbie idling issue!

[ben_jamin321]

Hi guys. I recently purchased this as my first bike about a month ago and have been having a blast on it! My only issue is with it’s idling. My problem is that when the engine has warmed up after about 10 minutes of riding, when I come to a stop at say a light or something, I have a hard time getting the engine to come back down to idling speed. So usually what I do is adjust the idle adjustment screw while I’m on the bike until the engine will idle on it’s own, but then it will idle at an rpm that is way too low; I have to stay on the throttle to keep it from dieing. 

So, I figure that perhaps the carbs just need to be cleaned and synched. I have already sprayed carb cleaner through the air intake to no avail. Do you think gummed up carbs might be the problem, or might it be something else? Also, if u think it is the carbs, should I try disassembleing and cleaning them myself, or pay to have it done? (I am in college and am quite tight on money!) I have a Clymer manual and like to think of myself as somewhat technically inclined. And lastly, if you think it is the carbs and this something I can do myself, should I get the carb rebuild kits, or maybe just the gaskets? Any suggestions???

Thanks much!

[Noel]

Yeah, it could well be your carbs.

Having said that, a carefully done basic tune-up is the place to start.

Valve clearances, ignition timing, plugs, the whole enchilada. Neither expensive nor difficult to do, but will use up most of an afternoon. Time well spent, IMO.

If after that the bike still doesn't run to your satisfaction, then look to the carbs. Rather than a complete teardown -- or the galactically expensive option of having the shop do the work -- get yourself a bottle of the magic elixir known around here as Yamaha brand carb cleaner and follow the directions on the bottle. It essentially entails mixing some cleaner with gas, injecting it down your fuel lines, and letting it sit for a while. Simple and genuinely effective, at least for carbs that aren't total wrecks to begin with.

[TwoTired]

My 78 Cb550K had your symptoms, even after a well deserved full tune up, finally cured with a good carb sync.  Had to do it twice, though I can't remember exactly why.  Might have been a leaking carb to intake coupler leak.

Cheers,

[ben_jamin321]

Thanks for the feedback! I will do the full tune-up before tackling the carbs. Can you suggest some of the absolute musts that I should do in this tune up??? Any feedback welcomed!!

[ProTeal55]

Can you suggest some of the absolute musts that I should do in this tune up??? Any feedback welcomed!!

1. Oli change / New filter
2. Spark plugs (check condition of sparkplug wires as well)
3. Check points
4. Grease whatever you can get your hands on
5. Check brakes for wear (repalce if needed)
6. Check tires for tread , rips, tears, etc..
7. Go over electrical system

[SteveD CB500F]

Adjust tappets
Tension camchain
Check clutch and throttle cables/adjustment.

[puppytrax]

Blow out or replace air filter
Check all accessible bolts for tightness - especially axle nuts, engine mounts, sprocket bolts/nuts
Check fuel petcock for leaks - shut off,  disconnect lines, and let sit with empty coffee can underneath  overnight

[Noel]

Absolute musts? Nope. Your bike runs.

Of course, if you want to run right, you should do the components of the standard tune-up which are likely to affect your particular problem:

New plugs
Inspect and replace or adjust points
Cam chain adjustment
Ignition timing
Valve clearances
Air cleaner service or replacement
Petcock strainer

THEN if you still have a problem, it's time to start monkeying with the carbs.

But wouldn't you feel silly if you spent a week unracking, cleaning, rebuilding, and synching your carbs just to find out that your air filter was clogged?

[KilgoreTrout]

Same deal is happening to me. I'll post results after a tuner uper.

[rob]

There is another magic elixir, SeaFoam, that you may want to try as well.  I have never used Yamaha Carb cleaner myself, but I hear its mystic powers are formidable.  If your like me and can't seem to find Yamaha Carb cleaner on store shelves anywhere, you may want to give SeaFoam a try.

Rob

[ben_jamin321]

Hey, thanks for all the great feeback! I replaced the plugs on my bike today and inspected the old ones. The left two, cyclinders 3 & 4 were covered in an oily black substance which I read probably indicates they are running too rich. The right two, cylinders 1 & 2, were a bit on the light side in terms of coloration, which i guess indicates they are running too lean. This would agree with the varying colors of my header pipes. I'm not quite sure how to adjust this, but I'm sure the Clymer will explain.

I've already adjusted the cam chain which is nice and quite now. I had to replace my fuel petcock as the old one broke. I checked the valve clearances and they seemed to be fne. All nuts and bolts are tight and I also cleaned out the air cleaner (wasn't that dirty). I also checked the points gap and they were fine.  This leaves the ignition timing. I am going to try and get my hands on a timing light and try to do this job myself.

I rode it around a bit today and the idling issue is still there. I think I will try to find this magic elixer that you speak of known as Yamaha Carb Cleaner, I'm very intrigued indeed!! I'm also taking the bike into the shop to have it looked at next week for a different issue - a mysterious rattle that I think is coming from either the clutch or trans, hopefully this won't be a big deal If you have any thoughts on this they're definitely welcome - prehaps i should start a different thread for this issue though...

I will let you all know what happens. Thanks again for your great suggestions!!

[Noel]

The rattle may well be normal. At idle, even a properly adjusted cam chain can make some noise. If it dissapears with a touch of throttle, you probably don't have a problem.

Your oily plugs, though, might be one. Have you done a compression check?

[ben_jamin321]

Thought I would give a quick update... sorry for the delay; being an engineering student doesn't allow much time for fun!

I timed the ignition and synched the carbs and am happy to report that the bike is running like a champ Even the "mysterious rattle" I was hearing is gone! Unfortunately, the idling issue still persists, though it seems to have improved to some extent. I'm going to keep looking for this "Yamaha Carb Cleaner", so far I've been unsuccessful in finding it. If that doesn't fix my problem then I might try taking the carbs apart and cleaning them. Will my riding the bike with possibly gunked up carbs do any damage???

Also, I think I may have miss-informed you all when I said that my left two plugs (cylinders 1 & 2) were oily; I should have said they were covered in a black sooty substance (carbon fouled?). I haven't done a compression test; my Clymer says to use a "compression tester", not quite sure what that is...

Noticed today that my forks seam to be leaking oil and also my steering is "sticky" near the center of it's arc; replace or re-pack stem bearings?? Seems like there's always something to be done on this bike! Thats half the fun though, atleast thats what I keep telling myself!

Guess that is it for now. As always, any feedback is gladly accepted