got a burble I cant fix

[itsacbx]

Hey all,
79 CBX with an 80 motor, but 79 carbs.
My bike has a K & N and Kerkers and I had the carbs off 4X, yes you read that right....FOUR freaking times.
There was an upside - I can now do a carb removal in 20 minutes tops!!!!!
My initial problem was created by giving the carbs to my local Vintage Club 'expert' who had just acquired a soda blaster - well f#@* me it took me a week to get what I thought was all the soda residue out of the carbs, but I obviously wasnt careful enough........
Either way I used a Randakks rebuild kit, read Mike Nixons book religiously [but obviously not well enough] then shoved her all back together.
Bike started perfectly but then ran on 1 or 4 or 2 or 6 cylinders .
Long story short it now idels perfectly and runs unbelievably well except for the burble/miss/stutter at a point where I believe the pilot jet doesnt function anymore as it transitions to the main jet. All jets are stock, O rings and seals/plugs in carbs are all new.
Im also starting to think it may have some megaphonitis from the Kerkers.
I did learn one valuable point [on top of all the other lessons], the measurement from the throttle slide to the bleed hole is CRITICAL bar none.
So we fixed that on about the third removal.
I tried a stock Honda air filter and the bike ran much worse, so back to the K & N.
Today I went for a long ride and above 100km the bike is exceptional, but under that it has this funny burble/stutter. When you open the throttle slowly it stutters then takes off normally.
On startup it idles at 1000rpm perfectly and sounds great. When moving away in first it stutters but accelerates very well but at 3-3500rpm it goes thru this burble/stutter period but in spite of that still pulls like a train.
Heres another sign that thinks arent right in cbxville. I pulled the plugs and 1,2 and 3 are perfect - brown electrode, slightly darker outer. Plugs 4,5,6 are sooty all over.
And theres more- header pipes on 1 is bright gold, 2 and 3 are bright blue/gold, 4/5/6 are dull slightly blue but not even close to the 1-3 pipes which supports the view of the plugs on 4/5/6 running cooler/sooty.
One thing I did when reassembling the carbs the last time was gave the accelerator pump some more oomph with a stronger spring and an extra washer.
I have the 80 carbs rebuilt and I think Im going to put those on and see if there is a difference. If its the same then its possibly pointing to weak coils or something else. Plugs are brand new one week ago.
Either way Im open to comments and suggestions.
Al

[steve murdoch icoa #5322]

I thought this had been sorted?
Most likely it is the K&N filter. Well known to cause a slight stumble in the mid-range.
The stock spring and washer are fine for the pump.

[daves79x]

Are you sure the choke plates for 4,5,6 are opening completely? Make sure your spring connector is intact and that you have a little slack in the cable when the choke lever is open. You are going way too rich on 4,5,6 and the is no electrical connection between any of them. It is fuel related. Choke not functioning properly, float levels too high, primary main jets and secondary main jets switched (I've seen this a couple of times). Switching back to the stock filter causing it to run richer is a dead give-away. Should note that all this assumes the idle/slow-speed circuits are clean and all the air bleeds are open - they may still not be.

Dave

[Jeff Bennetts]

Whatever Dave said!

Something else that displays your symptoms is a stuck or impeded carb slide, due to the carb tops not being in position before there tighten down, it's simple but can be overlooked.

[itsacbx]

I guess its sorted in one respect in that the bike is rideable and an absolute blast- Im just a bit of a perfectionist when it comes to how my bikes are to ride......and I dont like the nice colours on three pipes but not on three- its looks unbalanced and obviously is still not perfect!
Its definitely not choke related as I have slack in the cable and all plates are fully open.
Float levels are perfect also.
Its also not related to the balance between the carbs, meaning we did a very careful check to ensure banks 1 and 2 are opening together - we put two dial gauges on them so my engineer son could be satisfied they were opening together.
Even if the stutter/burble is related to the pipes Im OK with that, but the fact that 4/5/6 are running significantly richer is more my issue.
When I pull the carbs off today Ill check the primary and main jets again - and blow all the orifices and passages out again...now Im paranoid.
So I think Ill try the 80 carbs today and see what happens.
Thanks for the input.

[itsacbx]

actually I did have a stuck slide on #2 when I put the tops back on so had to loosen it off and redo it, so I checked all slides again at that time. Dont think thats the problem but will check them again of course.

[itsacbx]

well more work has paid dividends....bike is running as close to perfect as Ill ever get it and it appears to be as simple as refitting the K & N filter and checking all pilot jet settings to make sure they were all the same - one was out by a full turn and a couple of others by 1/4 -1/2 turn from where I thought they were set. Damn that Motion Pro adjuster tool is a handful to use....Im down to 3/4 turn out and the stutter is virtually gone. Any variance Ill put down to the pipes, but Im pretty happy with it, now I just have to fix the damn alternator rattle.
That I suspect is partly the usual plates banging away together, but I also think it needs a new bearing.
Thats a weekend project.
Al

[Rick Pope]

Don't postpone alternator bearings. They're silly cheap and easy to change, and a dragging bearing WILL toast the clutch plates, which are very expensive. Don't ask.........

The bearings are 6203 and 6201 at any decent auto parts store or bearing house. The seal is cheap from Honda. You can likely get all the pieces for $20 usd. Change everything while you're in there.

[Jeff Bennetts]

[daves79x]

Glad you've made good progress. How do the plugs look now? I've had the opportunity to rebuild quite a few sets of CBX carbs over the years that I know for sure had never been touched since leaving Japan. In every case, I've never found the pilot screws open more than 1 1/4 turns. This should tell us something. I used to set my rebuilds to 2 1/4-2 1/2 turns out, but was seeing some similar symptoms to yours. Low-mid range stumble. I now set all my rebuilds to 2 turns out and this seems to result in very crisp running, while still warming up pretty quickly.

Dave

[steve murdoch icoa #5322]

Thanks for that tip, Dave.

[itsacbx]

Yes I have bearings, just waiting for the seal from my local Honder dealer....
With the Kerkers and K & N and 1/2 pint of leaded gas per tank, my pilots are set at 3/4 turns out and the plugs across the 6 cylinders are as close to perfect as I could possibly ask. I ran some carb cleaner thru first and that definitley helped- maybe I had an orifice or passageway partially blocked ....either way Im now very happy with the way the bike runs. It starts perfectly on full choke and settles into exactly 1000rpm idle when warm, with no wavering of the idle rpm at all. I had checked the choke cable for free play and it was fine with some slack.
Thanks for the input and commentary.
Al