Topic: '77 cb550k synch or swim? carb. better!

[kerryb]

'77 cb550k.  slightly cold blooded, idles well after warm-up at any rpm you want. (down to 650).
Had a hanging idle issue.  That was cured after timing was readjusted to be right on.
good power in all gears.  valves adjusted, carbs cleaned several times.  boots seem tight, no changes when sprayed with WD-40.  carbs were synched a while back (before timing was fixed)
d7ea plugs all show nice tan color on electrode.  carb jets are stock (I forget what they were, but it was stock when I looked it up).  set mixture screws at 1 1/2 turns out to start.
Stock airbox and exhaust  carbs are pd 46A

AND THE QUESTION IS?  How come the idle mixture screws don't seem to have any effect except number 2.

Do I need to check Synch again, could it be dirty passages?  Is my Tach/Dwell meter not sensitive enough?
I'm tying to learn the best tune, where do I look next?

[bollingball]

Wait for it wait for it it does not change real fast. If you have a good ear you can hear it and it won't be much difference in sound got a pic of your tach. I have a old (40yrs.) sears model analog I think they still sell it or something close also have a LCD one but don't like it as much.

[TwoTired]

Is your tach capable of showing 50 RPM deviations?

You have a 550 tach or a 750?

Are all the head pipes the same temp?

The IMS screws get a reiterative adjustment cycle.  From an outward position they are adjusted inward just to the point where the most increase in idle speed occurs. Then the idle is brought back down with the main idle stop, and the next carb is adjusted, in turn and the process repeated with the main idle readjusted, etc.  After they are all done once, you go back and verify you found the true peak RPM for each IMS.

Right now from your report, I expect #2 is the dominant cylinder.

This may seems odd, but carbs can be cleaned, and they can also be cleaned thoroughly.  The former does not certify the later.  Sometimes, you have to clean the correct portion of the carb for beneficial effect.

If you are trying to cure a "slightly cold blooded" condition, it is probably not going to happen until you get the choke plates properly synchronized with the fast idle adjustment.  While cold, there will be a fast idle setting and choke plate position that will remove the cold blooded condition.  This will allow you to drive almost normally with the choke partially applied.  (Note, you will never get max power out of the engine with the choke plates interfering with throat pressures and airflow.  However, that is different than getting reliable power while cold, though.)
The choke is NOT simply an on or off mechanism.  The operator is expected to regulate the choke position during warm up, to obtain reliable operation.  This requires the operator to impart some skill upon the machine during the warm up period.

Modern vehicles use sensors and computers to remove skill and knowledge requirements from the operator.  New exposure to "the old ways" can leave those reliant on computers to be baffled.  The old bikes relied on sensors and computers located 2-3 feet above the seat, to obtain smooth operation.  Unfortunately, some of these computers, aren't programed correctly, (which actually has been that way since the old bikes were new).

Cheers,

[kerryb]

Ta Daaaa!!!  We're havin some fun now.
Here is a picture of my tach, it seems to be relatively accurate.  When the motor zooms a little, the needle moves a little.  keyword ;relatively.  So, I put in new plugs 'cause I had them.  New resistor plug caps too.  Synched the carbs again, they were really close, only one needed adjustment.  Then I started on the mixture screws being careful to wait for any change.  Each cylinder had a spot where the rpms increased slightly, maybe 50 rpm, but not more.  turning further had little effect so I put them back where the increase was.  Number three, not #2 seemed most dominant, but that is a topic I haven't heard of yet.

I'm not trying to cure the choke-to-start routine.  I learned it well on my Datsun 240z in the winter.  This bike only needs choke for 30 seconds or less.  You have to stay with it to prevent runaway rpm's.

Thanks for all the help, yes I've been paying attention and trying to follow advice

Idle is smooth at any level, can't wait for daylight to ride it and do a plug chop (at moderate speed)

I think I just need more practice to develop confidence, but hey, I have more bikes!  hee hee

...just for fun, kerry

[bollingball]

Glad you got it Hey that temp fuel tank looks like mine. That tach is good enough.

[DedHed]

Modern vehicles use sensors and computers to remove skill and knowledge requirements from the operator.  New exposure to "the old ways" can leave those reliant on computers to be baffled.  The old bikes relied on sensors and computers located 2-3 feet above the seat, to obtain smooth operation.  Unfortunately, some of these computers, aren't programed correctly, (which actually has been that way since the old bikes were new).

No truer words have been uttered!

These aren't the droids you're looking for.....

Phil