Topic: continuing 1981 cb650 carb problems possible solved

[redaccent]

Well I have my 1981 cb650c running fine, but I still have a hesitation above 5000 rpms.   I checked the plugs and they were black, and I have a strong spark on all.   So this is telling me that I'm running rich.
Just for kicks I removed the air box cover and just bolted the air filter to keep it from falling off.
The bike ran much better.   I can go over 5000 rpms, and go up to 80 mph and above with no problems.
The only problems I have is cold morning starts, just have to warm up more.

The question I have is do I have to change the jets or the jets are dirty still.  The bike has headers on it, and the carbs are exchanged rebuild.

Thanks,

John

[Caferacernoc]

That's a common mod for 650's actually. If your plugs start showing a normal tan then your jets are fine.

[cb650]

Did that to one last weekend.

[spudw]

i also have a 1981 cb650 and i had a hell of a time getting fuel into the bowls. it ran for a bit as long as i kept it above 3000 rpm. i have no air cleaner. a few minutes later it wouldnt start (a few sputters here n there but not enough to lay off the starter) so im wondering if the jets became clogged up again. i just cleaned the carbs out last week. should i clean them out again?

also i was wondering what the little knobs are on the bottom of each carb? they only turn one full turn until they hit a stop.

[750goes]

those little knobs will be the carb drain holes.

[DammitDan]

The carb drain holes aren't knobs, they're more like nipples facing straight down from the float bowls.  And there's a screw on the bottom of the float bowl that you can loosen to allow the bowl to drain.

Spudw,

You sure the knobs aren't the idle circuit adjustors?  Are the knobs on each of the carbs, on the front underside just behind the manifolds?

The 1980+ model CB650s have EPA caps on the screws to prevent you from turning them too far out (to protect the environment, of course  )  Is it the flange on the front of the knob that's keeping it from turning, or can it make more than one rotation if you're loosening it?

[Hush]

CB650 owner with also fuel problems, had read on a web site that these bikes run better without the airfilter cover, just replace the cover bolts with a couple of oversize washers and better breathing.
That's not my problem though, I have gas to my bowls and spark at the plugs but somewhere along the way the twain aint meeting!
Will watch your thread with interest.

[Jay B]

also i was wondering what the little knobs are on the bottom of each carb? they only turn one full turn until they hit a stop.

Those are probably the idle adjusters. They have a tang on them that hits the float bowls to limit adjustment, thanks to the EPA. Next time you have the bowls off you can grind off the tang on the head of it allowing more adjustment.

[cb650]

I ground the tab off the bowl.  The extra metal on the screw is nice to sometimes turn it by hand.

[spudw]

solved my issue... put more gas in fuel tank! lolz

now i just need to get carbs sync'd