Topic: 1980 CB650 Carb Problem

[650HELPER]

I have been working on and off for a few weeks to get a friends 650 running. Initially it would not start. I determined through this forum and other things that the carbs were not operating correctly, the bike had sat for 3-4 years without running. Ran fine before he put it away. After trying to clean with carb cleaner, I finally took the carb to a shop which cleaned it with an ultrasonic cleaner. Even after this, it seemed like the idle jets wern't fully open. When I tried to spray carb cleaner through the idle jets with the bowl off, I really couldn't see any fluid in the barrel of the carb. I also replaced the o-rings on the four air screws and put them back in with the same setting as original and one float valve.
Yesterday I tried to start the cycle, even though I wasn't sure about the idle jets. I fully choked the carb and set the idle slightly high before starting. It started within a few tries. It seemed to be running on only two cylinders (3&4) for awhile, then after a few minutes was running on all four. My problem is that whenever I tried to turn off the choke, the engine died, even if the engine was racing at 5-6000 RPM. The RPM's would decrease with even slight movement of the choke. This was after running for 10-15 minutes. Does anybody have any ideas on what to do next? Does this mean the carbs aren't getting enough gas?

[bender01]

Did you bench sync them before you put them back on?

[Gordon]

Unless you've forced compressed air through the idle jet circuit, you can't be sure that they're clear. 

[TwoTired]

There are four opening into the idle circuit that must be verified clear; the slow or idle jet, the slow air jet, The idle adjust screw and the opening into the carb throat.  I like to use aerosol carb cleaner to squirt into each opening as I can then see whether it exits the other openings.

I would also yank out the slow jets, clean them and then tap them back in. (Assuming you have pressed in slow jets.)

Cheers,

[650HELPER]

Thanks for the anwers.

I'm nervous about taking out the slow idle jets, but I guess I'll have to give it a try.

Ron

[tomkimberly]

Do you have CV carbs?

Tom

[CBJoe]

I would also yank out the slow jets, clean them and then tap them back in. (Assuming you have pressed in slow jets.)

Cheers,

Pardon my ignorance, but how to you "yank" out the slow jets without damaging them? I've been too chicken to try. I've got my '80 650C rack broken down to replace the air cut-off valves. 

thanks...Joe

[cb650]

a 80 shouldnt be CV carbs.   You dont yank out the jets just gently twist and pull.   I fought a set last year on my 80 and after pulling them 4or 5 times with no luck I put in another set I had and bike is going good now.




                              Terry

[TwoTired]

I would also yank out the slow jets, clean them and then tap them back in. (Assuming you have pressed in slow jets.)

Cheers,

Pardon my ignorance, but how to you "yank" out the slow jets without damaging them? I've been too chicken to try. I've got my '80 650C rack broken down to replace the air cut-off valves. 

thanks...Joe

There are different methods.  My favorite is to use a pair of soft jawed parallel pliers.  Others report using leather padding on channel locks or other type pliers.  Small marks on the outside of the jet body do not effect performance, though.  It's the inside that does the work/function.  Whatever method chosen, it's a brute force procedure.  Try to pull it straight out as there is a small emulsion tube projection on the blind side of the jet that is important not to damage.

Cheers,