CB 360 Running Rich on One Cylinder

M

motormayhem

Active Member
Hey guys,
My CB 360 as been running ok since I got it running after a 10+ year storage, but always had kind of a dead zone in the 2-3k rpm range where it seems like it is running with the choke on and then once it is past that it takes off. I pulled the carbs to check float height and everything. Both carb floats were set a little too low (overfilling bowls) so I raised both to .75in.

When I put the carbs back on the bike it ran great on one cylinder and the other would idle alright, but cuts out around 2k only lights back up around above 3k if your in the 30-70% throttle range. If I pull the plug on this cylinder and try to rev the bike on the working cylinder it revs up and down no problem, but if I pull the plug on the working cylinder this cylinder will only run the bike with a light amount of throttle and if you open it up it blows black smoke, rpm drops out to about 1200, and it will stall after about 30 sec or if you let off the throttle too fast. Since i've been doing this mostly with the air filters off I did notice this carb also has some gas mist coming out of it when it is chugging at full throttle and if you put your hand in front of the intake to that carb it will get wet with gas. Any ideas?
 
Shut fuel off and ran it on the bad cylinder and it ran like crap for about a min till it burned off some fuel and then it reved and was as responsive as it was running on the other cylinder. So I think its defiantly a carb related over fueling problem.
 
carnivorous chicken said:
Check float height again, and make sure the float valve isn't stuck/leaking. You also didn't say anything about adjusting your mixture.
Click to expand...

Also, check diaphragm for pinhole & sticking slide.
 
I re-checked float height and it is the same as the other carb at .750 in. Float needle and seat look good as well. Slide moves freely and returns. What mixture adjustments are there? I thought with the fixed jets only idle was adjustable and it idles ok, it's the 2k + that is a problem. Diaphram looks old but ok. I thought a leaking diagram would make it run lean by not lifting the float?
 
You've got an idle adjust screw -- I think one screw that mounts below the carbs on those CB360s -- and you've got an air/fuel mixture screw for each carb. Consult your manual.
 
carnivorous chicken said:
You've got an idle adjust screw -- I think one screw that mounts below the carbs on those CB360s -- and you've got an air/fuel mixture screw for each carb. Consult your manual.
Click to expand...

Right but that only adjusts idle mix which is ok.
 
First, do you have a manual? If not, get one and read it.
Don't rule out the mixture screw.
Can't remember if those things have jet needle adjustments, it's been a while, but I know it's possible to shim them if need be.
When you say the float needle "looks OK" because it slides up and down, it doesn't sound like you've actually made sure that it stops fuel flow when it's supposed to. Take off your float bowl, put a rag under your carb, turn the fuel back on, and manually close the valve by pressing up on the float. Does it actually stop fuel flow?
 
I have the manual and rebuild page for the carbs and have read them. I did play with the idle mix screw and it didn't seems to change much. I was hard to tell but it did seems to lean it out a little at idle, but didn't have as much effect as the adjustment on the other carb did (bike will still fire the cylinder with it all the way closed where when I turn the other carb adjustment in it will cut out on that cylinder). I looked at the seats and float needle and there were no surface defects or anything to prevent it from sealing. I will double check by holding the float closed, but they look brand new. There is no fuel coming out the overflow tube or carb when the bike sits with the fuel on which I would think it would do if the float was stuck open., but who knows. The slide I was referring to was the needle slide for the secondary main jet. It moves freely and lifts when I open the throttle and it looks like that is where the majority of the fuel is coming from when that cylinder is being over fueled.
 
You probably need carb sync, the adjuster is between carbs, hole in frame is for adjuster tool.
I've posted a vid on it
 
Currently they are adjusted by ear and rpm drop when you pull a plug, but I am planning on using gauges as soon as I can buy the stuff for that. I got it to run a little better by adjusting the float height to 21mm.
 
Took the carbs all the way down to the housing and built them back up and the seem better, need a sync for sure but not unrideable now.
 
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