Questions about my 1980 CB 650

If it's broken or just needs tweaked

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jessakin4
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Joined: Sat Nov 03, 2007 4:04 pm
Location: Kansas City, MO

Questions about my 1980 CB 650

Postby jessakin4 » Sat Nov 03, 2007 4:13 pm

Hello, my name is Jay, I just picked up a 1980 cb 650 and it was running rich. I fixed the float settings and the problem was solved. But, now the carbs still need to be sync'd and I don't know how to do it. Could anyone give me some advice?
Also, I'm having an issue with stalling. I think it might be the clutch but I don't know. I generally have to keep the choke halfway engaged and it occasionally will drop rpm's completely and stall. Does this sound like a clutch problem or does anyone know? When it stalls in this fashion it takes awhile to get it started back up. I rode for around two hours yesterday with no issues but I would like to avoid them in the future.
Thanks for having this site by the way. It's a great resource. :)
Jay Akin

Pinhead
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Postby Pinhead » Sat Nov 03, 2007 11:02 pm

I've never sync'd carbs so I can't help you there. However, I had a stalling problem with my bike for a while, and found it to be a weak charging system, which in turn made my spark pretty weak. Check your charging voltage, plug cap resistance, and go from there to verify your ignition system is working at its peak. A weak ignition system will show up as a lack of power from 1000 to about 3000, extremely easy to stall, and hard to start once it dies. It'll seem like it's running very lean at the low rev's since the fuel is not ignition due to the weak ignition.

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Buber
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Postby Buber » Sun Nov 04, 2007 7:00 am

Syncing carbs is one of the easiest things to do. Here's the home-made equipment:

Image

You simply need to balance the vacuum on all carbs. I won't be going through the whole procedure here - just search the internet for carb synching. The tool is a vinyl pipe, filled with old engine oil, connected to the vacuum inlet on the carbs.

It's all really easy & straightforward. You need good screwdriver, though. Carb 3 is a bitch to get to the screw....

Good luck!

jessakin4
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Joined: Sat Nov 03, 2007 4:04 pm
Location: Kansas City, MO

Postby jessakin4 » Sun Nov 04, 2007 2:14 pm

Thanks for the tips. I think it may be the weak spark you mentioned with my rpms cause it almost always happens if I get the rpms up and then let them drop. I'll look up carb syncing on the web, thanks.
Jay Akin

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Volker_P
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Re: Questions about my 1980 CB 650

Postby Volker_P » Mon Nov 05, 2007 3:10 am

Welcome here! :D
The CB is a fine bike and usually it is not to hard to get it running reasonably provided nothing is really wrong. So my first tip, as you just got the bike and you know nothing about it, first check ignition as you can get crazy concentrating on carbs when you have an (additional?) ignition problem. New plugs are a good investment if only just to exclude them a the source of all the trouble.

Well, if you have to ride with the choke half way engaged, I think your carb problem is not solved yet. Don't hope too much to get a real improvement from carb syncronization. In contrast, a syncronization effort in that state could bring some undefined result which may cause rather trouble than benefit when you finally go to fix the carbs correctly afterwards. In the chronology, carb syncronization is the last thing to do when everything else is verified to be correct. For your present state of error detection, it is sufficient that the gaps of the four carbs pistons at idle look rather equal.

Stalling at low rpm (from too lean) would be what I expect as a consequence when one tries to compensate too large mains with a lower floater level. It may run well at medium to full load, but low and idle would be too lean. There you could keep it alive only with the choke flaps. But starting when hot with half choke should be not so easy. Sounds familar? :roll:
So from what you write, there is no reason to look for a clutch problem. You probably switched from too rich to too lean. Make sure you have the correct jetting and set the floater level to the correct value (and don't forget to clarify before whether your ignition system is allright).
In case you need a manual and you did not find one yet by reading around here, there is an online manual e.g. at http://cosky0.tripod.com/ and http://cosky1.tripod.com/

Good luck!

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Ibsen
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Postby Ibsen » Mon Nov 05, 2007 6:51 am

I agree with Volker. And synchronizing the carbs should be the final part of the tuning. The air filter, float levels, cam chain. valves, spark plugs and ignition has to be adjusted and in good working order before you do the synch.
What you can expect from a carb synch is that the engine will be running smoother both at idle with less or no noise noise from the clutch and the primary drive, and at minor and middle throttle openings. If the carbs are way out of synch you will also have a power loss since the cylinders will try to run at different speeds.

I have bought a Morgan Carbtune for my bikes:

viewtopic.php?t=10

jessakin4
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Joined: Sat Nov 03, 2007 4:04 pm
Location: Kansas City, MO

Hey!

Postby jessakin4 » Mon Nov 05, 2007 7:44 pm

I've been putting in some serious hours on the bike to break it back in, it's been stored for a few years now, and I only stall or need the choke when the engine is cold. Is there anything in this? Also, my jet settings are just my guess work, how can I find a way to set them back to the factory settings?
Speaking of an air filter, I have a tear in my air box tube I've just discovered. (Not the one that connects to the engine.) So I'll be replacing that this weekend. I've already replaced the sparks and checked the gaps. Honestly I'm thinking they aren't sync'd and it just needs to be broken back in b/c it seems to be running better everyday.
Jay Akin

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Volker_P
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Re: Questions about my 1980 CB 650

Postby Volker_P » Tue Nov 06, 2007 2:19 am

Well, the CB needs the choke always and quite long when it is cold, but from
jessakin4 wrote:I generally have to keep the choke halfway engaged

I concluded that this is presently your normal riding condition which would be suspicious. Good that this was a misunderstanding. I guess then you are not too far away from a reasonable setup. The leaky air box tube is a reason for too lean, getting it tight will provide further improvement. When you checked up everything (especially that you are not too lean, Ibsen provided a good list what to check), do an extended trip at changing revs and loads. Maybe it will run much better afterwards, at least that was the way to reanimate my CB after winter riding with short and slow trips that the engine does not really seem to like. If you did not change the oil yet, after this turn it is the right time to do it. If it still seems necessary then (or you just want to do it), you also can try carb synchronization.

You already got proposals for carb balancers, one more from me: If you have only one vacuum gauge, you can connect it with hoses and T-connectors and use clamps to block the lines successively. This way you can adjust 1 vs 2, 3 vs 2 and finally 4 vs 2 (2 is the reference as it has no adjuster screw). It may not be really convenient but it worked fine. :wink:


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