81 CB650C.....

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PAVALKER
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81 CB650C.....

Postby PAVALKER » Wed Dec 12, 2012 10:57 pm

I recently picked up another 81 CB650, but it was in need of some minor repairs (fork seals, caliper seals), a fuel tank and a battery. I robbed the tank and battery off of my other CB650 to get this running and tinker with it for a bit. Might just have to keep the tank and battery on this one.... I'm liking the fairing. It also came with a trunk (not pictured) and the rack for it rotates the trunk up over the passenger seat so it becomes a backrest for the rider.... and its easy to put on/take off.

I'm searching for a tank for the other one... but might have to modify a tank from something else and make that one a bobber or cafe... or sell it as is. It is a low mileage nice runner. So if anyone has a nice tank.... let me know.

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Volker_P
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Re: 81 CB650C.....

Postby Volker_P » Thu Dec 13, 2012 2:09 am

Congratulations!
This bike looks like it is in excellent condition. :D
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PAVALKER
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Re: 81 CB650C.....

Postby PAVALKER » Thu Dec 13, 2012 10:38 am

Thanks. It is in really nice condition, as is the other one I robbed the tank/battery from. They both needed a good deep cleaning. However, this one is in need of some more tinkering.... it might have a fuel or timing condition that is holding it back from it's full potential.... it starts to stumble (cut out) at 4500 rpm under load (riding) that I discovered yesterday. In due time I will get it I'm sure. I have not yet pulled plugs, will probably get new ones, and am also waiting for a new fuel filter as well.

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Volker_P
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Re: 81 CB650C.....

Postby Volker_P » Fri Dec 14, 2012 3:07 am

Vaccum shutoff (if it has) may be another issue for that.
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues

If you really like this site and you would not like to see it vanish soon, have a look there: Urgent: Future of HondaCB650.com Forum

PAVALKER
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Re: 81 CB650C.....

Postby PAVALKER » Fri Dec 14, 2012 12:31 pm

Volker_P wrote:Vaccum shutoff (if it has) may be another issue for that.


Do tell.... can you elaborate? I checked plugs, they were a little sooty and I cleaned em. Timing is on (static test).... have to get a new timing light to check dynamic and also spark advance.

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Folsoml
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Re: 81 CB650C.....

Postby Folsoml » Fri Dec 14, 2012 12:49 pm

The vacuum shutoffs are horrible on these. Most of us have removed them. Just make sure you shut off the petcock when the bike is parked.
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PAVALKER
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Re: 81 CB650C.....

Postby PAVALKER » Fri Dec 14, 2012 2:05 pm

Have to study this a bit.... do I need plug or caps?


Besides shutting off fuel at the vacuum shut off (based on engine vacuum), what problems could this be introducing into the system to cause my stumbling issue?


For testing purposes.... could I just take the fuel line from the petcock to the center fitting on the carbs, then plug/cap the top two fittings where the line goes to and comes out of (leaving the vacuum shut off in place)????

PAVALKER
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Re: 81 CB650C.....

Postby PAVALKER » Fri Dec 14, 2012 8:31 pm

Whoa..... looking at both bikes (carbs)... they appear to be the same but the newer one has an additional vacuum line Teed off the one above and appears to go down between nr1 and 2 carb on the rear side. The other one appears to have just the one line as indicated above. Were there different configurations or is this some user modification?


Upon further inspection, I see that the older CB650 has the vacuum line T's between 1/2 and 3/4 carbs removed with some modification and sealer, whereas the new one has those T's in place going to the airbox somehow.

Can someone enlighten me on why the difference and what those T's do?

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Folsoml
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Re: 81 CB650C.....

Postby Folsoml » Sat Dec 15, 2012 5:12 am

The T's are vents. They should have the tubes that go to the airbox. The one without them is a PO modification.

I would assume you could leave the actual vacuum shutoff in place and simply bypass it. With regards to the plugging or capping question, I put a little rubber cap on the brass fitting that comes out of the carb.
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PAVALKER
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Re: 81 CB650C.....

Postby PAVALKER » Sat Dec 15, 2012 11:00 am

A lot of searching and reading...... and although I found out the T's are vents, some say are important and some don't, it makes one ponder why the one without the vent T's runs great and the one with does not? I also found out that it could very well be a fuel issue, an air issue or even an electrical issue... Guess I need to make a plan and check everything out.

PAVALKER
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Re: 81 CB650C.....

Postby PAVALKER » Sat Dec 15, 2012 6:57 pm

After much reading last night, and knowing that the spark plugs indicated a rich condition (black soot) I removed the cover for the air cleaner and held the filter in place with fender washers. I took it for a ride..... WOW, ran like a raped ape. I went back home and put the cover back on, just in case it was the seafoam that cleaned out a clog. Another ride with the cover on it ran better than it had earlier, but not as good as without the cover, and it stumbled at 6k rpm on occasion. Took the cover off and again great. I took it out, ran it hard and it died on me.... I switched it to reserve got it running.... then went to fill it up. Guess running rich it ran thru a good bit of gas. I will check the plugs later this week and confirm their color/condition. It is kinda of weather dependent on getting it out for a test ride.... today was great, next week its colder and wet.

I did notice an oil spot on the garage floor... like a Harley marking it's territory ..... and it's from the shifter seal which shouldn't be too bad. My 73 Honda CL350 doesn't leak and I don't want this one passing on bad habits to the others in the stable.

bubbachicken
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Re: 81 CB650C.....

Postby bubbachicken » Tue Dec 18, 2012 11:45 pm

Folsoml wrote:The vacuum shutoffs are horrible on these. Most of us have removed them. Just make sure you shut off the petcock when the bike is parked.



Ok... Now, mine seems to have a fuel leak someplace on this vacuum shutoff unit (I think it is a bad fuel line at the connection going toward the carbs). I would like to know more about what this unit does, and what removing it from the system (i.e., bypassing it) does to how well the bike runs (before I do something that harms it or myself). I also am having an issue with cold starts, but that is for another thread (will post that elsewhere, so as not to jack this one entirely). Can I simply plug the vacuum lines to the shutoff unit, route fuel directly to carbs without playing with mixture settings, and gain some stability in the engine (or perhaps a little mileage?)? Will the bike start easier?

onepieceatatime
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Re: 81 CB650C.....

Postby onepieceatatime » Wed Dec 19, 2012 1:01 am

bubbachicken wrote:
Folsoml wrote:The vacuum shutoffs are horrible on these. Most of us have removed them. Just make sure you shut off the petcock when the bike is parked.



Ok... Now, mine seems to have a fuel leak someplace on this vacuum shutoff unit (I think it is a bad fuel line at the connection going toward the carbs). I would like to know more about what this unit does, and what removing it from the system (i.e., bypassing it) does to how well the bike runs (before I do something that harms it or myself). I also am having an issue with cold starts, but that is for another thread (will post that elsewhere, so as not to jack this one entirely). Can I simply plug the vacuum lines to the shutoff unit, route fuel directly to carbs without playing with mixture settings, and gain some stability in the engine (or perhaps a little mileage?)? Will the bike start easier?


The vacuum shutoff was an added safety feature starting on the '81 model. It is there for when people forget to turn off the petcock. All it really does, is block the flow of fuel when there is no vacuum to the diaphragm. Without it, if the petcock is left open when the bike is off, and the carb floats stick, fuel can flow out of the carb bowls and create a fire hazard. Just plug the brass vacuum port on the carb and run the fuell line from the petcock to the carbs to bypass it.
Folsoml wrote: Good judgement comes from experience. Experience comes from bad judgement. :lol:


1977 CB750K
1977 CB750K
1978 CB400A
1980 CB650C
1980 CB650
1982 CB900F
1982 CM450A
1997 GL1500SE

PAVALKER
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Re: 81 CB650C.....

Postby PAVALKER » Wed Dec 19, 2012 9:09 pm

If the vacuum shutoff is operating as it should, and it's just a hose leaking, I would recommend you just replace the hose. Hoses get dried out and leaks occur, and are easily replaced. If the vacuum shutoff is leaking.... then it might be easier to just bypass than fix. But it does serve a function... IMO

bubbachicken
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Re: 81 CB650C.....

Postby bubbachicken » Wed Dec 19, 2012 11:02 pm

PAVALKER wrote:If the vacuum shutoff is operating as it should, and it's just a hose leaking, I would recommend you just replace the hose. Hoses get dried out and leaks occur, and are easily replaced. If the vacuum shutoff is leaking.... then it might be easier to just bypass than fix. But it does serve a function... IMO


True.. It also makes me keep on my toes as far as the MSF training goes... I suppose I might leave it alone...


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