Cannot get to idle.

[new81cb650c]

Hello again-

I have not been here for a while because I put off my problems. I got a newer bike that has no problem other than it gets low on gas after a good ride. I cannot get the Honda to idle and it is loading up with fuel.

Let me give you the history on my 81 CB650C. I bought it with the tank, seat, and carb assembly off the bike. This bike has been liscensed since purchased but has not been moved for the last 11 years. It had 800 miles when I got it and now has 1200 from short runs to see how the adjustments did. I can't get any adjustment out of the idle knob. When I let off the throttle it dies. Seems to run great from 7000 rpms down to about 2000. But then stumbles and dies.

Here is a list off things that I have did or replaced:
Relined the tank that was rusted with three part product called Kreem.
replaced all four floats
replaced plugs twice
changed oil and filter twice
changed engine side clamps
changed air box side clamps
replaced all pilot screws
replaced float needles
soaked and cleaned whole assembly
checked and adjusted valve clearance
changed air filter twice
checked compression - all cylinders within range
checked static timing - with specs.

My wife would now like to ride with me and am about ready to dump it in the river. Any direction would be apprecited.

Is this a weak spark or ignition problem. Or is it sucking air in somewhere.

Thanks in advanced

[Chris]

Hello.

What color were the plugs that you replaced? If they were black (rich), could your choke be stuck closed or not functioning properly? When I first got my CB650, I was fouling plugs out right and left because I was using too much choke for too long. In this Summer weather, you shouldn't need full choke for more than a couple of minutes and should be at 'no choke' within a mile or two at most. Once these plugs are fouled by rich mixture, it's virtually impossible (in my opinion) to clean them sufficiently for reuse. And equally impossible to get the 650 to idle... or to even keep it running for that matter with said plugs.

Also, for a quick check to see if it's sucking air, try blocking off the airbox with your hand or a rag and see what happens. Some people like to spray WD-40 or some other liquid around possible vacuum leaks and listen for a change in running characteristics. I don't have much experience at that personally, but it's a fairly common procedure. I've shyed away from it for fear of starting a fire. Has anyone else tried this method?

-Chris-

One more thing, if the engine is in fact sucking air, it would cause a lean mixture. Your plugs would be white or even melted from a lean condition. As opposed to black from rich condition.

[Volker_P]

My wife would now like to ride with me and am about ready to dump it in the river. Any direction would be apprecited.

I would recommend the Rhine river. I offer to prepare the usual environmental protection modifications for free.

After a that extended standing time and/or the tank rust problems you reported last year, a complete disassembly and cleaning of the carbs sometimes is the only way to get rid of stubborn deposits. As it runs perfectly at higher revs, the small channels of the idle system are suspicious rather than weak ignition or spark. The latter would also mean hard to impossible starting.
Another but quite improbable option at a 1000mls bike would be the carbs being badly out of sync. But first make sure there is no more dirt or rust in any corners. An ultrasonic cleaner may help. For soaking, the Yamaha carb cleaner is often recommended. I am not sure if it is still available as some components are somewhat problematic.

[chucksklrst]

Hello again-

I have not been here for a while because I put off my problems. I got a newer bike that has no problem other than it gets low on gas after a good ride. I cannot get the Honda to idle and it is loading up with fuel.

Let me give you the history on my 81 CB650C. I bought it with the tank, seat, and carb assembly off the bike. This bike has been liscensed since purchased but has not been moved for the last 11 years. It had 800 miles when I got it and now has 1200 from short runs to see how the adjustments did. I can't get any adjustment out of the idle knob. When I let off the throttle it dies. Seems to run great from 7000 rpms down to about 2000. But then stumbles and dies.


Thanks in advanced

Make sure your float level is correct. Are the carbs flooding out by letting in too much fuel to the bowl. I had that problem on my KLR 650 before. Only would run with an full open throttle. Symtom of this is, dies at lower RPM's, Runs rich, uses lots of fuel. Good luck Let us know what you find.

[new81cb650c]

Thanks for suggestions so far I will try (check) some of, all of, those issues and get back to you.

wish me the best

[cb650]

If it hasnt been changed a US 81 has CV carbs with plastic floats that aren't adjustable.




Terry