Topic: '79 cb650 inconsistent idle

[scott_cb650]

I have a ’79 cb650 that I purchased in August of ’05.
I removed the carburetors in December and thoroughly cleaned, set the float heights, replaced the valve needles, reinstalled and balanced them.
The carburetor boots, from the carburetor to the manifold were suspect but it was running OK.
Well two weeks ago the motor started revving to high RPMs without coming back down.
I had to release the clutch and put a load on the motor to get it to decelerate.

I figured my carburetor boots had finally cracked or I would at least need to rule out that problem so I spent the buck$ to buy new boots.
While the carburetors were off I removed the float bowls to make sure everything was still clean, it was.
The low speed jets are hard to clean since they are pressed in and I can’t remove them.  I tried but they wouldn’t budge, so I just ran a piece of wire brush wire through them and sprayed Berryman cleaner through.

Now after reassembly it runs greats but doesn’t quite idle right.
Even when I'm in neutral and let off of the throttle, it decelerates to 2500 RPM rather quickly but then it slowly decelerates after that.
There's a real fine line to get it to idle at 1 speed.
I'm trying to get it to idle between 1000 and 1500 RPMs.
When I try to adjust the idle with the idle adjusting knob it either drops from 2000 RPM to 1500 and then start to accelerate, sometimes up past 3000 RPM.
OR it will continue to slowly decelerate from 2000 RPM down to 750 RPM where it promptly dies.

What are my options on adjusting the idle besides the big “idle adjustment knob”?

[Gordon]

You need to synchronize the carbs.  There are other things that may or may not be contributing to this problem, but what you described is a classic symptom of unbalanced carburetors.  And with all that pulling, rebuilding and cleaning of the carbs, they're definitely out of balance. 

[KB02]

You need to synchronize the carbs.  There are other things that may or may not be contributing to this problem, but what you described is a classic symptom of unbalanced carburetors.  And with all that pulling, rebuilding and cleaning of the carbs, they're definitely out of balance. 

I agree.

ALSO, when you bought the new Boots, did you buy new clamps to go with them? Sometimes the stock clamps strech over time and don't form the tight seal they once did.  If you didn't, get a new set, and then balance the carbs.

[scott_cb650]

Thanks, I'll try balancing them and let you know how it goes.

Scott

[scott_cb650]

Well balancing didn't work!
They're still in balance but it won't idle.
Pressed in idle jets are clear.
Accelerator pump works.

Seems to be an air leak somewhere but I can't find it.

Brand new boots engine side boot are on.

Still searching . . . .

[DammitDan]

How about adjusting the pilot screws?  It may be a combination of poorly adjusted screws and a idle adjustment knob set too high.

What do your plugs look like?  Also, did you check the air cutoff valves on the carbs when you had them disassembled?

[scott_cb650]

Thanks D..Dan.
I'll check those things when I get back.
I'm off on a vacation the way it is.

It's really just a problem at idle which is bearable for now.

Me and the bride (of 18 years) are going on a trip from Hot Spring to Eureka Springs and back the next day.
I can't wait!