Air Cut-off Valve versus Carb #1 pilot screw

[neighborcat]

Hello All:

'82 CBX, 8K miles, just revived from storage by off-bike carb cleaning, brake rebuild, etc. Carbs were much less fouled than I expected after 4 years of un-prepped storage.

Symptom: Cylinders 2-6 fall right into idle mixture adjustment at 2-2.5 turns out. Cylinder 1 doesn't fire smoothly until 4.5-5 turns out, right about where the pilot screw shaft pulls out of the O-ring.

I have: Verified float levels using "clear tube" method with bike running
Verified good seal at boots, synch vacuum port, bowls, slide caps, etc.
Verified strong spark and correct plug gap.
Verified passage from pilot screw to port in throat to slow jet in bowl is clear.
Verified correct valve clearances
Verified throttle plate and choke plate positions relative to other cylinders.
Verified air passages/transfer tubes between carbs 1, 2 and 3 are open.
Verified pilot screw/spring/washer/o-ring are not damaged by swapping with #6
Visually inspected # 1 pilot screw seat with magnifying glass
Verified slide action, smoooth

I have found: Perforated air cut-off diaphragm. If I understand the passage routing, the effects of a cut-off valve leak on the #1 carb should be eliminated by sealing the vacuum passage to the #1 intake, but this has no effect on the problem.

The engine runs like scalded cat from 2K rpm on up, so this is definitely an idle circuit problem. On the plus side, I can now remove and reinstall the carbs in under an hour, have come to enjoy the taste of carb cleaner, and have taught my daughters many new and fascinating words. The motorcycle used to make Daddy happy, but now he keeps taking it apart gets upset when he puts it back together and starts it.

What am I missing?

[alimey4u2]

What am I missing?

Not a sense of humor, great first post & welcome to the site...

Sooo, In a nutshell # 1 cylinder won't idle until you almost screw the idle jet out of its threads & it looks like you've tried everything possible apart from "carb balance" ??

[daves79x]

I'm guessing (not really guessing - just a whole bunch of experience) that #1 idle circuitry is still plugged. The #35 slow jet is removable in the '82 carbs, so you should have been able to get it as clean as the rest. I'd say maybe the air bleed is still plugged. You need to be able to spray cleaner in every idle orifice either way. The idle air bleed is the one under the aircut-off valve for #1 carb.

Set all the air screws to 2 1/2 turns out and leave them there. Then look at the butterflies and make sure all are equal. It's easier if you expose a tiny bit of the orifice in the throat (about where they should be for correct idle anyway) and make sure all are the same.

Good luck

Dave

[neighborcat]

This is what I get for my neglect, I know. I had carefully balanced the carb vacuum just before storing the bike, so yes Mr. Benjamin, your summary of the issue is spot on.

I got out my 14mm Occam's Razor (a great diagnostic tool) and as you say, decided to have another go at those bleedin' air passages. We shall see.

But other than a richer open throttle mixture across the board, does a cracked air cutoff diaphragm have any effects specific to #1?

You know, my Whisperlite camp stove has this bit of cable that runs inside the fuel line from the fuel bottle, through the evaporator, and to the orifice. The orifice itself has this tiny weight behind it with a nipple that just fits the orifice. If the stove gets clogged, you pull the cable out and thread it back in, and shake the stove so the little weighted nipple pokes around through the orifice, and Voila! (that's French for "Your sh*t works again.")

I'm thinking either these carbs need some tiny cables and weights, or my stove should be fuel injected.