Topic: Variety of issues on 78 cb550k4

[crazyxxhondaxx]

Hello folks!
Summer is here and I hit the pavement every spare second i have. Ive put on a thousand miles since i rebuilt the top end (all to stock specs) and got the bike running again last August. It runs better now than ever before but it still needs more.
 Ive cleaned the carbs, set the floats and synced my carbs but it still has a hard time running a consistent idle. I have to set the screw way in to idle it when cold, and turn it way down when it warms up all the way. And after its been ridden for 15 or so it idles well at 1600 but no lower. When its colder itll run at 1900-2000 range at idle. Drop below and it dies.
The bike as an aftermarket baffled 4-2 shorty exhaust the Previous previous owner put on, stock airbox and jetting. I live at 5000 ft in wyoming. So my primary theory is that the reduced back pressure from the exhaust matched with stock jets is the culprit. Before I begin to tear into them again i wanted more feedback and what else it could be? Timing is spot on with a brand new points assembly and engine pulls well, speedometer is off by a somewhat unknown margin but i believe ive had it near its limit.
My second but more concerning issues is there is a mildly aggressive chuckle in the front handle bars in the 40-45 range that goes away quickly after and doesnt show back up all throw the entire range. Also of note when loaded with myself (185) and passenger  (140) there is no chuckle what so ever. I replaced the front tire last year and the shop that did it checked all my spokes and balanced it and it was all as it should be. The original theory was a flat spot on the tire from sitting over winter but after 900 miles and no improvement thats  been ruled out.
Is it an axle bearing or steering bearing?  I was shopping around and because of the general affordability of the bearings ive found, allsballs brand,  i was considering replacing the steering and front bearing and just to be thorough i was going to do the rear as well. Am i goinv the right direction with this or could it be some other factor i haven't considered? 

Thanks for any advice and sorry about the ramble!
Have a safe and adventurous 4th!

[links56]

Sounds like you may need a slightly bigger pilot jet. As for the main jets, how hot is the motor after a ride? Have you done a plug read? I would check that out. if you can screw the pilot air adjustment screw all the way in and it still runs you don't have the right size pilot jet. If it's to small it makes me wonder if the other stock jets are undersized a little. Sometimes it's hard to notice that its running a little lean which makes the engine run hotter and therefor reduces engine component life.

If you stay at the speed the handlebar "chuckle" starts, does it keep doing it? Is the "chuckle" an up and down vibration or a side to side wobble?

[Deltarider]

Begin with the simplest and verify if the tachometer is telling the truth. I once worked on a CB550K3 (identical in this respect) and had a hard time to have it idle well. Turned out a true 1100 rpm showed 1700 on the onboard tachometer. If your tacho is correct, we can look at other possible causes. But remember, although the idle jets on 550K3/K4 models are suspect (they clog up easily if the bike isn't used regularly), ignition comes first for a check.

My second but more concerning issues is there is a mildly aggressive chuckle in the front handle bars in the 40-45 range that goes away quickly after and doesnt show back up all throw the entire range.

In that speedrange it is not an uncommon phenomenon. Many bikes of all sorts of makes suffer from it. Some have it a little, some more. You can chase the origin (it has to do with the geometry and some interference) or live with it. If it's serious, it needs to be adressed ofcourse and maybe some expert in this forum (and not the usual hailshooters like me) can give you a checklist with items in order of priority. If it's minor (like on my bike) just keep your hands on the handlebars at all time.

[crazyxxhondaxx]

Hello folks!
sorry for the extremely late response but works been super busy.
I have to order a new pairs of tires, so we'll see how that translates for the speed wobble. My old tires split on the walls unfortunately. I was thinking I would probably get the Michelin Pilot Activs.
To answer questions first:
1. The speed wobble maintains if I coast at the 40-45 range, but after a little bit of throttle it dies down. It is most definitely a side to side motion.
2. Since this is my first motorcycle and I don't have the chance to ride any others I couldn't really tell you about exceptional heat, however after a longish ride the engine stays too hot to touch for about 10 minutes or so.

How do I check to see if my tach is reading true?


However I have run a few diagnostic tests as suggested by you gents and I have two main discoveries
1. The bike runs with the air screws screwed in all the way.
2. I believe the motors been running relatively to really lean, I pulled spark plugs 1 n 4 and pictured below, but I forgot the socket I use to get to 2/3 at work so I cant pull those right now.
Ill try to recheck the ignition timing tomorrow when I pick up some more of my tools. But when I installed the new points plate this spring I had it timed right.

So if my stock jetting is running too lean which size of jets should I go too? I understand some rejetting is guess work but as a starting point? I live at 5000 ft so theres that to consider too. I run with a stock air filter and aftermarket exhaust that was on when I bought the bike. theyre small 9 inch trumpets with a baffle.
The bike gets ridden frequently and if not ridden I at least fire it up and let it idle.

thank you so much for all your help! I hope to get her back on the road soon.

[jonda500]

having to turn up the idle speed if you want it to idle when cold is normal for these bikes - and then having to wind it back out substancially once warm is also normal- I only play with the idle speed screw when the engine is fully warm, but I have fitted a throttle stop screw which I use to hold the throttle open a little when I first start up.

My 500 had a similar low speed handle bar shimmy to what you describe- when I replaced the old front tyre (3.5" pirelli supersport) with a new michelin pilot active, it completely cured the problem!
John

[jonda500]

"if not ridden I at least fire it up and let it idle"

I used to do this to my bike, but will never do it again now that I know it's doing more harm than good - the engine doesn't get sufficiently warm to evaporate/burn off harmful combustion vapuors/residues from inside the combustion chambers, and the muffler(s) will be left with water vapour coating and corroding the insides. And unless you ride it for at least about 15 minutes the battery will actually be flatter than it was before you started!
John

[Desert Dan]

Most engines start having issues breathing above 4000ft with your stock air box and aftermarket exhaust I would think you would be pretty close to stock jetting at your altitude. I usually run any carbureted engines with slightly more advance on the ignition at altitude to maintain a nice idle and better performance, with a timing light try upping your ignition timing so that the F is underneath the timing mark instead of the actual fire mark this should give you 2-4 more degrees of advance which should make it so your engine runs cooler gets better gas millage and runs better ay idle.

[crazyxxhondaxx]

jonda: thank you very much for that information! I'm glad I rarely have to do that, until just recently it was my daily commuter.

calj/desert dan: I'll be testing the ignition advance today after I finish staining my new work bench, the graphic is very helpful so thank you calj. Also thank you for clarifying the specific bearings, would it be worth it to replace the rear axle bearings as well? Ill have the tire off anyways to get the new ones put on when they come in.

[harisuluv]

set the idle to where it is good when it is warm.  when it's cold, use the choke instead of the idle set screw to adjust it.  is your choke working?

[crazyxxhondaxx]

the choke works, ive checked the butterfly valves and everything seems to work as its supposed to.

[harisuluv]

If the choke works, why are you using the idle screw to adjust?

Checking the butterflies move is only verification that they move.  There is still the cable, the choke linkage, proper reassembly etc. 

For example, recently a guy said his choke worked fine and the butterflies moved.  But his choke wasn't actually working cause he was working it with missing parts and using a coat hangar to actuate it.

If it's working right, you shouldn't have to rely on using the idle screw so much.

[crazyxxhondaxx]

Well I guess I was running under the assumption that the choke always pulled back in as you pulled it out? The knob that is. Also After I hold in the choke for a while the engine will surge up to 3000 rpm and hold for a few second then come back down after I push it back in,  is that indicative of a bad linkage?

Calj: Which bushing in particular? I'm looking at a pivot bushing and a pivot thrust bushing, just replace both or one or the other?