1981 CB650C

[VintageRider]

9487180A-13D1-40A8-A75B-B816DE7D17DB.jpeg (8.16 MiB) Viewed 23441 times

Got it last week with the intention of learning some mechanics.
Currently not working. Some lights turn on, others don’t. Engine turns over bit a little tight (took spark plugs out and put some oil)

Gas Tank is also not in a good shape: failed liner and rust under peeling liner…

Previous owner told me it might have starter clutch problems (i hope not as i understand that is a major task, see some instructions on doing it without opening engine in half).

So, my plan is:
- check if starter clutch is working or not.
- if starter clutch works, do compression test, check spark, clean carburetors, drain/replace oil, attempt to remove liner (acetone or MEK), clean it, re-lined it(?)

If starter clutch slipping…attempt to replace it following some of the tutorials posted somewhere in this forum

If i get it to run, take it apart, clean as much as i can (do not have a blaster of any kind). Maybe repaint frame depending on status, try to find an original seat and grab bar

Any other suggestions?

I know this will take me several months if not a year (if i am able to get it to run)

[Volker_P]

Welcome here!

Needs some care but looks still like in good shape. The stickers and the stock rear sprocket suggest that this bike has not seen that many miles. The 4-4 exhaust also still looks reasonable. So you very probably have a good basis there.
Looks like the engine side carb clamps are missing.

Tank and starter clutch are known issues. Nothing wrong about your planned proceeding.
As electric issues are very annoying I also would have a very close look at that 40 year old harness. I even would disconnect every single plug and clean the contacts before putting them together again before I would try a first serious ride.

BTW, you learn a lot on your bike during cleaning parts so this is not a waste of time. In fact cleaning stuff often is the most time consuming and also most important issue in any work on old bikes or cars.

Before you are going to to some mechanic work, read the corresponding chapter in the workshop manual to get an idea on the order of things to do and of hidden bolts etc.. Makes much more sense than working until you get stuck and then have a look into the manual.
If you are not common to motorcycles be aware that these bolt threads in Japanese alumina parts are quite soft. If you want to go into the engine you really need a torque wrench of small enough torque range. Also keep to the stepwise (un-)bolt patterns for cylinder head and cover. Otherwise it will most probably end up in buying a family size package of helicoils.

Have fun!

[VintageRider]

Hi Volker,
Good to see you still read/reply on the forum. Had learn so much from you (older posts) already in just one week since i got the bike.
I think i confirmed the starter clutch issue. It engages some times (I see the bolt on the ignition timing spinning), other times it just sounds but not spinning. If i manually move the bolt to move the engine a couple of turns and try again, it engages... so I order the sprint, spring cap and roller. I see there is an older post by Buber explaining how to do it with the engine on frame and unscrewing the clutch while inside the engine (there is a YouTube video by @BuildSomethingAuto following that approach). My question is: in that approach, it is not clear if it is possible to torque the screws back while inside the engine. The approach from Kerryb has more steps in order to take the whole clutch and unscrew it outside of the engine...

BTW: I doublecheck and the engine side carb clamps are there (upside down so not visible in the picture).

Besides that I am just learning, my major concern now is sourcing parts, it seems there are less and less parts you could source from Honda and used parts are either too expensive or non-existing. For instance i took the Petcock out and the filter screen disintegrated, it seems my only option is to buy a "new" petcock. I guess I will be a constant when i go further down on the rebuild.

[Volker_P]

If you are able to get the starter clutch disassembled inside, you should be able to get it together there, too. Good idea to be really attentive during disassemble and take many pictures.
This is my point of view but for you the work that you are going to do has to fit your capabilities, your available tools and your experience.
E.g. at viewtopic.php?f=4&t=2806 you find something that can be done successfully in principle but is not recommended that way even for experts.
If you have instructions for the starter clutch job that appear more promising to your situation, follow them.

In few cases the starter clutch housing turned out damaged in a way that the torx heads were not accessible any more.
Unfortunately this means you would have to remove and split the engine in this case.

In fact meanwhile parts are a serious issue and you might even get stuck completely. 3D printing may solve this problem sooner or later but waiting for that is probably not yet a realistic option.

I think it should be possible to find some replacement for the petcock filter screen that fits. The original screen is anyway too coarse to avoid idle jet issues. I think there are repair sets for a leaky petcock. One has to drill the rivets for installation. Note that the 1980 and 1981 petcocks have different threads.

[VintageRider]

While i wait on the starter clutch parts, i took the carburators (keihin VB44B) off the bike. I noticed the “Vent T with rubber connection tubes” are missing. Any idea if they can be sourced (have searched for hours and haven’t found anything) or instructions on how to fabricate them?


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[Volker_P]

Some people here successfully installed aquarium equipment from a pet shop.
If you do not like to trust that plastic stuff with fuel even small stainless steel T's may be available that way.

[VintageRider]

I don’t think i will trust aquarium fittings. Will probably buy the part on ebay (I think i found a couple) Or buy a similar full carburetor on a salvage Place.
But to be certain, what version is this? It says VB44B but there is an A in a square after. So not sure if this is a VB44B or VB44A as i see there are abc types
and not sure if that even matter. None of the fuel/vent pipes were connected or there when i got the bike so knowing for sure the type would help to reconnect in case the type makes a difference (i downloaded the “Carb Rebuilding Honda DOHC-4’s” and seems to match what i got)



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[Volker_P]

VB44B

[VintageRider]

The procedure to remove the starter clutch worked and wasn’t that hard. The springs are not OEM and somehow there were two springs on one of the holes. And one of the screws holding the clutch had become lose, there is a little bulge on the clutch. I flattened on the vise.

There is signs of wear where the rollers sit…smooth with fine sandpaper?

There are some on eBay but from the pictures they don’t seem better that mine. So i will replace all springs, rollers and caps and reinstall and see. If still not working will try one from ebay






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[VintageRider]

Starter clutch back in the bike and seems to now be engaging all the time (i will put the cover back with gasket maker as i do not have the gasket and haven’t found it locally).
Next task would be cleaning carburetors, check valves, tensioner. And hopefully try to start it.


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[Volker_P]

That's good news.
Also good to know that this kind of marks seem not to hinder functionality.

[VintageRider]

Hi,
I cleaned carburetors (fully disassembled, multiple times on the ultrasonic cleaner with simple green, lots of carburetor cleaner in passages, air compresor).
Unfortunately i damaged the spring that links chocks 1/2 and 3/4 (i know manual and other posts warn about it). Applied temporary fix (zip ties as others have done). Will be in looking for a replacement.
I did bench synch. Put it in back on the bike and was able to fire it. With choke it starts at 1800-2k rpm (i think is supposed to be higher) but starts climbing very quick and have to remove the choke right away (it was 8 Celsius inside the garage). I only tried a couple of times and didn’t let running long. Pilot screws are at 2turns out, that it what it was when i checked before cleaning (but bike was not running when i purchased so PO may have moved them). Not sure i undestand the fast speed idle adjustment.

In any case, it is already -3 degrees in the garage so i will have to wait until April or so to work on tunings carbs.

How many turns out is are pilot screws for this bike with this carbs?

In the mean time , i will disassemble the bike, clean, check components, put new tires, assemble for when it gets warm again.
And learn how to ride and get a license


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[Volker_P]

Good to hear about your progress.
As you said fine tuning of carbs at this temperatures does not make much sense. When you come back to the idle screws in spring, have a look here:

viewtopic.php?f=4&t=11695

Kind of complicated procedure but the reactions look promising.

Merry Christmas and a happy new year to you and all who still read here!

[kerryb]

Welcome to the forum Vintagerider, this may be the quietest forum that isn't dead yet, but we're still trying to keep it alive. Congrats on the starter cllutch repair, if it doesn't hold, the clutch I got came from a small 3 wheeler (atc 125?) At a good price and it was perfect.
Are you here in the states or over on the big Island?
I plan to return to mine as soon as the current project is finished.

[VintageRider]

Hi Kerryb,
I am in Ontario, Canada.
Weather here is surprisingly warm for this time of the year so i fire the bike one last time to empty the carburetor .
I couldn’t get it to properly idle (it idles at almost 4k). Pilot screws or black knob did not have any effect so carbs are probably out of sync or binding and not properly closing) and one of the cilinders didn’t fire (there is spark so will re-clean that carb) i read some of the threads on this forum regarding the high idle problem and will try again late spring
I decided to fully disable the bike, spray paint the frame, clean the engine on the outside (no sand blasting, soda blasting as i do not have tools) and assemble back cleaning/inspecting/replacing what is broken (and replacement exist)


Having some hard time removing rear wheel (over tightened).
Having second toughs on repainting the frame. It is cold and i am afraid that would affect painting curing.

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