CB360 idle issues

How long did the bike sit you think? Mine sat at least 15 years give or take a week or two. The valve seats were pretty rusted even though it was in a storage unit. A quick lapping took care of that issue though. Pull the carbs and the exhaust and turn the engine over really slowly and listen for the hiss, if you hear it your valves are not sealing. Really easy fix if you can get the head off and can find a valve spring compressor.

When I did the oil part of the compression check on my machine before I tore it apart it jumped WAY up not just 10 pounds like 30-40 a side. I found later after I measured everything on my engine that it was SHOT according to Hoyle (the manual).
 
You mentioned that it can take a while to return to idle and that the revs sort of stick? That's also a symptom of running rich. You did adjust the air mixture screws already, right?
 
The last time it was registered was in 1994 so yeah, about 15+ years.

frogman said:
A quick lapping took care of that issue though.
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I did notice some hissing after adjusting the valves. So head off, valve lapping compound and twist away until it's all fitting perfectly right? Never done lapping before, but I'm willing to take on the challenge.


Sonreir said:
You mentioned that it can take a while to return to idle and that the revs sort of stick? That's also a symptom of running rich. You did adjust the air mixture screws already, right?
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I have adjusted the mixture screws starting about 1.5 turns out from seated. My problem is my idle isn't consistent enough for me to even hear it go up or down. I know it's run rich at some point in this process because the plugs are fouled.


I'll adjust the valves on both sides (possibly followed by attending to my valve seats/stems fit) and replace my fouled plugs and go from there. Still on the to-do list is syncing the carbs (waiting for vacuum adapters from PJ), followed by adjusting the idle.


So we agree that I don't need to replace the rings/pistons? If so, that really makes my day cause I was dreading that.
 
The true test for the valves is to pull the head stand it on the ports with the combustion chamber facing you. Pour some acetone (finger nail polish remover) or rubbing alcohol into the ports on the top and see if any leaks past the valves. Should be very obvious but you can leave it sit for a few minutes and see if you see any leaks. Then dump the ports flip the head over and do the other side. Just don't let the wife catch you stealing her remover ;) If they leak then you can pull the head apart and check for bent valves and cruddy seats and do a lapping if need be.

While the head is off I would get some Seafoam or something like it and get the pistons about half way down the bores and pour some in on top of them just in case the rings may be stuck. Let it soak in a while. That crap will also eat any of the carbon off the top of the pistons and will do wonders for the combustion chamber as well.

After all that, put it back together and see if you have fixed your issues. Might change the oil after the Seafoam deal as well.

As far as pistons and rings getting replaced work on ONE thing at a time, if the valves leak start there and work down.
 
I wonder why my valves were leaking compression?


Heh, working on cleaning and lapping them now.

IMG_20110519_100023.jpg
 
:o WOW, That's bunch of CRAP!!! Looks like someone can get to scrubbing, what do the cylinders look like?
 
Cylinders weren't bad, some seafoam and a brush and they were shining. They held the seafoam for a couple hours before I cleaned it out too! So that is good news pointing to not having to redo pistons and rings. I'm hoping the blackness means it was running rich because I can't find anywhere it would be leaking oil as the pistons and rings were well sealed.

I'm planning on reseting the idle air mixture screws once I get it all put back together to make sure it's no longer running rich. I think the PO had no idea about pretty much everything.
 
Running rich is a whole nuther animal and gasoline from 30-15 years ago was not what is now. Part of maintenance of older engines was to periodically clean the crap out of the combustion chambers because the gas sucked ass. What you see is all that left over crap from back then. IF anything that means the bike never really spent any time running hard for a long period of time, say 45 mins at highway speeds once or twice a week, it would blow that crap out if it did. (COBS) ;)

I'd lap the valves scrub the shit out of everything, and put her back together and see what you get on a compression test. THEN worry about the rest, don't touch the carbs until then. IF anything turn the idle mixture screws 1 1/4 out from softly seated.
 
Sigh...cleaned the chamber and valves, lapped the valves (they held rubbing alcohol for 20+ mins with no leaks) and put it all back together, adjusted everything, and kicked it - psi was 130 or so, jumped to about 150 with a dab of oil in the plug hole. When I turned the engine over slowly, with carbs out and mufflers off, and listened I heard air leaking from below the head (aka not the valves). Piston/rings? Head gasket? The head gasket looked perfect and the rings held seafoam so I don't know what it is. Maybe holding seafoam doesn't necessarily mean the pistons/rings were good? Anyway, I'll probably tear it all apart this weekend. Where can I get new rings? Thoughts? tips? tircks? suggestions? I've never done pistons/rings before, so anything helps. Thanks a ton.
 
How can you diagnose that? Also I notice in the exploded views that there is an o-ring between the head and the head gasket. My bike didn't have that, should I try that first?
 
Burning oil or oil leaking out of the head is the easiest way to tell. You can also spray some soapy water around the joints and turn the engine over. Look for bubbles to appear in leaky places.

You didn't reuse the head gasket did you? You can also check for warping of the head mating surfaces the next time you have it off. It needs to be less than .3mm.

The most reliable way to check for leaks is a full leak-down test though. If you're still chasing compression problems after what's been done, I suggest this is as the next course of action.
 
Also.. let me add: Compression ratings of 150, while not great, will not contribute to poor idling. That's enough compression to idle just fine, you'll just be down some power once you're moving.
 
Yes, I reused the head gasket (trying to save on money). Burning oil can also be a rings problem though right? How can you know if it's the gasket or the rings when doing a leak down test? No oil is coming out of the head gasket from the outside. Would I be able to tell if the gasket is good just by looking at it with the head pulled out? I'll test with soapy water but should I just replace it no matter what? I mean it is 37 years old.


Back to another question - does the piston holding liquid point to rings being fine? What makes you think head gasket instead of rings? Any ideas about the o-ring I mentioned in my previous post?


I really don't want to do rings but I will if I must.
 
Back from a 3 week vacation and I need to figure this out. I took the top end apart again so that I could replace the head gasket. Got it all back together and when I turn the engine over slowly I can hear air leaking from the below the head gasket (like in the jugs). Makes me think rings are in my future. Any thoughts?
 
I checked the compression with the bike cold and got about 135psi on both cylinders (I verified it three times for each cylinder to make sure it was accurate). I put the carbs back on and re-timed everything (points and valves) and checked valve clearance. When I try to fire her back up (via kick or starter) it won't start. Every 4 kicks or so I get a VERY loud back fire. I tried starting it via the starter and noticed fire balls out the exhaust ever 3-4 seconds or so. I pulled my plugs and grounded them on the head and turned it over a few times. Spark is good. Plugs don't seem wet but I'm not sure how to tell.


So what's my problem? Why won't it start up again? Thanks in advance.
 
I have a CB450 in my CB360 Frame. However, my CB450 did something very similiar to what you discribe. I increased my jetting. Solved problem and runs much better over all and takes throttle nicelt even when it is cold on the bottom.
 
Remove points cover and 'flash' points with a screwdriver and check the plug you think should fire fires.
Common problem when advancer has been disassembled and rebuilt wrong.
If it is the case, there is one way to fix it and a bodge that works.
Correct thing to do is dismantle and assemble properly, bodge, swap blue and yellow wires at coil/condenser connector
 
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