Topic: '81 CB650A Running Problems

[CB650Tex]

Got a new (to me) '81 CB650A - don't think it had been running much, if at all, for at least a few years, though it started up easily when I went to see it.

Done the obvious to get it working and pass the inspection (check brakes, new brake fluid, new plugs, oil and filter change, new tires, get the lights all working, change gear shift shaft oil seal) and it runs but not very well.

Various problems:

1) Needs at least a small amount of starting fluid into the airbox to get started, unless it's been running a while.

2) In neutral, RPM fluctuates of its own accord.  Sometimes it's worse than others.

3) Backfires out of the exhaust periodically.  More frequently, get dark smoke out of the exhaust.

Have sprayed WD40 onto boots from carb-to-cylinders and carb-to-airbox - no effect.

Not done anything to the carbs yet  but am guessing I have to do that next - cleaning and replacing bits at least.

Anything else to try before that?  Not too keen on the whole carb synching idea - don't want to make it worse than already is.

[Crusty_Butt]

Have sprayed WD40 onto boots from carb-to-cylinders and carb-to-airbox - no effect.
Not done anything to the carbs yet but am guessing I have to do that next - cleaning and replacing bits at least.
Anything else to try before that? Not too keen on the whole carb synching idea - don't want to make it worse than already is.

If its anything like the 650c here are some things you can check (all things that have given me trouble with mine):

Make sure your choke plates open and close. The plates operate off a cam so if they are stuck you can still push/pull the cable and think its working when it isn't. Get some new spark plug boots if yours are old. Make sure the charging system is working. Make sure the gas tank is filled with fresh gas. Make sure the vacuum thing that shuts the gas off doesn't have a hole in the diaphragm. Make sure the ignition advance unit turns freely.

I would pull the carbs and clean them anyway. You should be able to without buying kits as long as you are careful with the little o-rings on the ends of the idle screw adjusters.

Good luck.

Bret

[tomkimberly]

You are describing the exact same problems I had with my 1981 CB650C. Those carbs are a bear to keep the pilot jet ports open. The problem is they are pressed in and I never could figure how to remove them for a proper cleaning.

My solution was to search Ebay and find a set of carbs from a 1982 model. THey will be stamped on the sides as VB44B (or VB44C). The ones you have are stamped VB44A. The VB44B and "C" pilot jets are removable meaning you can get them clean.

I considered sending the 81 carbs off to have them sonic cleaned but decided in the long run the cost to replace them was less that to send them out for cleaning every few years. BTW, only the VB44A, VB44B, and VB44C carbs will interchange. The carbs from 1980 and earlier will not fit nor will carbs from 83 and beyond work either.

Tom

[CB650Tex]

So I've just taken the carbs off - what a pantomime that was, ended up stripping out a whole load more stuff than the Haynes manual suggested and then it was still a bit of brute force and ignorance to get the carbs out of the connecting hoses to the engine...

Anyhoo, got them off to discover that some previous idiot owner has obviously taken a real disliking to the carbs:

1) Two of the idle adjuster screws have been replaced with some botched up thing with wire loops brazed on to the end of the threaded part, instead of having the regular ends with screwdriver slots.  No big deal as the carb rebuild kits I've just got from Z1 Enterprises have replacements.

2) Now for the biggy - the attachment point for the pull end of the throttle cable is broken.  One of the two prongs that should go around the nipple on the end of the cable is simply not there!  Somebody had drilled a hole in the cable end nipple and then wirelocked the cable nipple to the remaining prong arm.

So my questions today are:

Has anyone else seen this breakage before?  If so, how have you fixed it?  Am assuming that it will be v. expensive/difficult to get a new part...

If I need to get at this piece to sort out a fix, can I break the carb bank in half easily enough, without upsetting too much?  Or can you only pull it apart one carb at a time?

[Ibsen]

I haven't heard of this breakage on the throttle cable pulley before, but it is very common for the plastic connection for the choke cable.

http://www.sohc4.us/forums/index.php?topic=1035.0

[Crusty_Butt]

I hated taking those carbs off at first. I take two of the airbox rubbers out of the airbox, makes it alot easier. You can put the carbs back in then put the two airbox rubbers in last. I put a little grease on all the intake rubbers to make it easier.

The cb500 I have has the same breakage you describe, but its on the push cable.

The 1&2 cabs seperate from the 3&4 carbs very easily. The fuel crossover tubes have o-rings on the ends. Don't reuse them or they could leak and you would have to do this all over again.(don't ask me how I know) Don't separate the 1&2 or 3&4 from each other.

Maybe you can fix that pully by welding or some sort of jb weld repair. You might be better off picking up some carbs off ebay, or maybe rig them up the way the previous owner did, if it doesn't look dangerous.

Make sure you use compressed air to blow out the idle jets/passages. Don't put the carbs back together until you are absolutely certain the air flows through the idle jet and exits through the tiny little holes next to the butterflies. This will save you alot of trouble in the future if you get this right the first time.

Good luck.

Bret

[CB650Tex]

Yeah, that's what we ended up doing too - we ended up removing all four rubbers from the airbox to the carbs and the big hose from the air filter housing to the airbox.  Had to hold the airbox back with tie wraps then as it had so much space to move about in!

One thing baffled me though - the lower mounting bolt for the air filter housing doesn't have a captive nut.  Why?  Where do they find people to make such dumb designs?!

re:o-rings on the fuel crossover tubes - thanks for the tip.  Any suggestions on replacements?

re:repairing the broken throttle arm - this may be a dumb questiuon, but what is a jb weld repair?

Will be looking for a set of carbs on ebay but am not too hopeful of finding a decent, reasonably priced set quickly...all the ones I've seen so far are in pretty grotty condition (and not the right sort anyhow!).

[Crusty_Butt]

re:o-rings on the fuel crossover tubes - thanks for the tip.  Any suggestions on replacements?

I got lucky, the Harley shop down the street had a big Keihin o-ring set and I took the old ones in and found some that matched. Maybe your carb kits have them. Maybe you will get lucky and yours will be in good shape. Mine were cracked and leaked.

re:repairing the broken throttle arm - this may be a dumb questiuon, but what is a jb weld repair?

JB weld is a two part epoxy. You might be able shape a piece of metal and glue it to the pully with JB weld or some other epoxy.

Bret

[tomkimberly]

Will be looking for a set of carbs on ebay but am not too hopeful of finding a decent, reasonably priced set quickly...all the ones I've seen so far are in pretty grotty condition (and not the right sort anyhow!).

If you are looking for replacements, make sure you get a set of VB44B or VB44C carbs and use your VB44A carbs as a door stop.

Tom