Topic: 81 CB650 carb and choke problems

[Nashbuilder]

I will try and make this quick and clear:
Bike sat for about 4 years, has not been running properly for 8+ years. I have taken the carbs off and cleaned them well without dismantling them. I pulled all the jets out, pilot screws and anything that was possible to remove I took it out and cleaned it. I did do a rebuild kit. Multiple people saw them off the bike and said they looked clean and in pretty good shape. I have installed them and now the trouble begins.

With choke on (closed) the bike starts up and idles at 1500RPM for about 5 minutes then it slowly starts to rev getting up to 3000. At this point I have slowly pushed the choke in to open it up. As I do this the idle comes back down. Once it is open all the way the bike dies. I tried restarting it with the choke off (open) and the bike started no problem but instantly revved to 7000RPM which I then turned the key off to keep from red lining. I adjusted the pilot screws in to make it a little more lean thinking maybe there mixture was to rich.

What the heck is going on?

[trueblue]

Are your carb slides and throttle butterflies free and closing off properly, I'm assuming this bike has cv carbs.

[thrutheframe]

  Did you check the accelerator pump diaphragm?  Is the spring in there?  Just a thought.

[cb650]

Idle jet?    None removable on the 81.  Did u clean the tank out too?

[Nashbuilder]

Yes CV Carbs -There is a chance the throttle is not closing properly, is there away of adjusting this while on the bike?
I did clean the tank with electrolysis. The accelerator pump diaphragm seems fine and the spring is in there, however it does seem a little varnishy but all seems to be ok with it. No rips, tears, holes in it. But is that something that could hold open and cause the random high revving?

The throttle is a big suspect to me. When I finished cleaning them I had to spray the throttle with WD40 to get it to function.

I am a rookie at working on motorcycle so thank you for your advise and tips.

[fmctm1sw]

There are a couple threads around here (mie is one of them) dealing with the '81 650 and CV carbs.  Lots of good info in them.

[Nashbuilder]

I believe the search doesnt work or I am not using it properly. I have typed in Cb650, 650 and it says your search returned no results. Im not this dumb....where the heck is the proper search for these threads that deal with 81 650's. Can you link one or two of them. I also scrolled through every post in the carb topic and there was only one listed a 650 in the subject.

[onepieceatatime]

search feature is broken. Site administrators are working on it.

[cb650]

Look under other bikes.  There is a couple threads on the dohc 750 and has the same carbs as the 81 82 650's.  One has a link to a good carb rebuild article.

[Nashbuilder]

I took the carbs off checked the main jets and they are still clean, Floats seem fine, choke plates are all in unison, throttle plates move in unison. I took the push cable off which was keeping the throttle from snapping back closed. Now with only 1 cable the throttle works very nicely.

Today with the choke on I revved the engine a little but when I let go of the throttle and is snapped back the RPM's stayed up at 4000, then slowly idles down to 1200. This happened 2-3 times until the 4th and it shut off instead of hold idle at 1200. Any suggestions?

My 81 650 has VB44A CV carbs.

[trueblue]

Sounds like your cables are a little tight you need a bit of slack in the cables otherwise they will bind, the other thing to check is that the throttle slides are free to move (the pistons inside not the butterflies), they should just fall back slowly when you lift them up with no restriction, I have a set of carbs here with varnish on the slides that I need to clean, and this causes hanging idle.

[tomkimberly]

My 81 650 has VB44A CV carbs.

The slow jets (idle jets) are clogged. Either soak the carbs in a sonic cleaner for 8 hours or more or do what I did and purchase a set of VB44B or VB44C carbs. The B's and C's have screw in pilot jets.

Tom

[Nashbuilder]

Tom - there is no good way of cleaning those out with a wire of any sort? Only dismantling and soaking or purchasing new ones?

[tomkimberly]

I could never get the 44A'a clean enough to get it to start and run consistently. I fould a set of 44C's, bike starts up 1st time every time. YMMV.

I gave those 44A'a to someone here, I don't think he ever got them to work either.

Tom