Boggy idle

[Kitsune84]

Have my carbs off for cleaning right now, but here's the problem as it existed before I yanked the carbs:

For awhile I had an inline fuel filter that I realized was choking off the gas- nothing was getting through. I replaced the inline with an in-tank filter, slapped the bugger back together and...

With the inline, the bike started without a second thought. I barely heard the starter sometimes, she'd just start right up- would take revving ok, but died when I gave her wrist in gear to ride off until she was very warm, and if I choked her, RPMs would shoot up to 4000.

Without the inline, she started a little rough, took a few tries, and needed to be choked for quite awhile. Wouldn't take throttle unless she was quite warm, even a small flick of the wrist would kill her. Eventually, she was warm enough to be revved, but obviously this isn't 'ideal'.

To head off air leaks at the boots, I wiped some silicone gasket goo around the carb boots at the head and plan on putting a thin bead around the outer lip of the carbs as I reinstall them...

Cleaned the carbs, there was a little crap in the carbs (little black flecks, some kind of jelly-like but otherwise unidentifiable orange goo, Bench-synched, but they all seemed to be set the same. I don't have a vacuum syncing tool, but was wondering if thus far my issues could be corrected without?

Lightly seated the pilot screws and screwed them out 1 5/8 as per the shop manual... they were out 3, not sure if that 'out 3' setting would rich it out too much or not?

Haven't pulled the plugs yet, but I will when I have time.

[Buber]

MIxture screws - if they are on the "engine" side then turning out is richening. If they are on the "airbox" side, then it's leaning.

Bench syncing - this is only to check if the engine will go. But to judge the tickover they MUST be synchronized. You don't need teh vacuum tool - you can do it yourself. check this:


There are lots of descriptions how to do it, I can only say that it works.
As per bogging - try to go for a while without the airbox cover or even air filter - but ONLY for a short, 1 mile test. if it gets better, then you mixture is too rich. Or just check the spark plugs.

And tell us what was the outcome Good luck!

[Kitsune84]

this is another dumb question, but in adjusting the slides, (I have the mechanical carbs) how do I ideally hold the adjustment stud still as I tighten the locknut?

[Volker_P]

The CB650 is known to need choke for a while and you can't expect a good throttle response as long as the engine is cold without choke. It may start on 2 or 3 only and run on all four after half a minute or so. So far that's nothing to worry. However when warm it should idle smoothly around 1000rpm when the carbs are synced reasonably. However also a weak ignition (or just very old or dirty plugs) could be responsible for poor idle behaviour. Ignition and valve settings (and everything else) should be all right before you consider synchronization with a vacuum method. Otherwise it may end up anywhere and/or drive you crazy.

[Kitsune84]

How do I best test ignition? I have what appears to at least be decent spark at all plugs (bluish white) and the bike kicks out 13.4-14.5v to the battery... the wires from coils to caps are new-to-me, but a little used (as are the caps...) but if I'm still getting decent spark, does that matter?
1000rpms seems REALLY low for the idle, but I guess that's what the 79 manual says as well. geez. mine idles okay at 1500... haven't tried 1000 yet. Oddly, when I try to adjust the idle screw, the lowest it goes is around 1000... then it stops connecting with the throttle cam altogether. Weird. any idea why that would happen?

[Volker_P]

I could imagine that the throttle cam does not move further as soon as one carb piston seats at its bottom position. If carbs are out of sync, others may be still open too much for 1000rpm. So this could be some hint that in fact your carbs need synchronization. Nothing to worry about so far.
With that voltage and good spark at low rpm, ignitions seems not problematic. However you never know how sparks look like under pressure. Cables need not to look brand new from outside, they should show no cracks in insulation and moreover the inner copper part should be all right (not green).
You really should take time to pull plugs as here is the only panel which will could tell you a bit what happens inside your engine. Do all plugs look equal? Or do they only look equal in two pairs?

[Kitsune84]

Well here're my plugs- bear in mind, this is mostly just from an hour long ride, then starting 'er up after little work here and there (futzing with the electrics, futzing with the new filter system/removing the inline filter... that's pretty much it. Would've done a plug chop, but I honestly just don't want to ride it too long before I get the carbs figured out and synced, just don't want to do any damage...



If you can't see well enough, 4 looks kind of a coffee brown, 3 has some white under the little arm, but everywhere else is a bit more brown... 2 is shiny black, but not wet. Where it's not oilish black/brown, it's toasty brown. 1 is black pretty much all over, not necessarily really oily, but not very sooty either.

My theory is that the bike is generally leaning on that left side, so it would stand to reason that if I start it right away after having sat it straight up, it might still be a bit rich on that side... but that doesn't explain the discrepancy between 3 and 4. Let me know what you think. It could be missing on 3, because I do hear a "skk, skk..... skk......." sound while she's warming up, like she's missing, then eventually it goes away as the bike warms up.

Edit: I should add, she has good compression and I've replaced all the valve seals, lapped in the valves, etc... She had some small oil leaks when I first started her, but they seem (?) to have dried up, as far as I know...

[Volker_P]

That's what I call a precise answer!
Usually you should have a look directly after the extended turn and avoid short starting before it. Anyway this seems still useful. Seems no ignition common circuit problem as there is rather 1+2 and 3+4 similar than 1+4 and 2+3. The balck one is the one who is temporarily missing, #1 in your case.
With regard you have already started a few times, I'd say 2+4 are all right, 3 might be a bit lean and 1 is too rich or has weak spark due to some reason.
I'd check ignition cable, plug cap and spark plug of #1 (e.g. exchange with #4) and floater level of #3 for possibly being a bit too low.
As you did a valve job, re-check settings because if the valves run in a bit (what they should not do) this could end up in zero gap what is really bad!.
BTW, your plugs don't look that bad that you would get a serious problem from riding on like that.