Carb troubles

[JARichmond]

Hey everyone. I'm in need of help. I have a 1982 Heritage special that I've been working on for way too long. Here's my problem today:
When I start the bike on full choke, It settles down at 2k rpm, revs all the way up to 5-6k on its own, and then 10 seconds later it falls back down to a steady idle for a while and then dies. It won't run with the choke off or half on for very long without bogging down and dying. My left spark plug is black (rich) so I recently dialed the mix screw back a half turn but haven't run it to test it out, and the right plug is a little light (but I'm leaving it as is for now). I just replaced my exhaust gaskets, so I know they're good. I also did a carb cleaning to too long ago
Can someone tell me why I'm having this issue and what I can do to rectify it?

 

[226dark]

Sounds like it is running on one cylinder (possibly spark related) then when the other cylinder fires up the revs will jump high. Once both cylinders are firing you would adjust the idle from 5-6k down to normal.

 

[01ps]

-The carbs have to be REALLY clean to run properly, not just a squirt of carb cleaner, but completely disassembled and every port cleaned.
-Check the rubber diaphragms in the top of the carbs for holes.
-Make sure the mixture needle orings are actually there.
-Make sure your intake boots (carb mounts) are not cracked or leaking.
-And your carbs may be way out of sync so build a manometer and balance the carbs.

 

[226dark]

My left spark plug is black (rich) so I recently dialed the mix screw back a half turn

When you say dialed back
Turning it out (lefty) allows more air in, yes but that increase in air through passage draws more fuel making it richer. Turning in (clockwise, right) leaner.

 

[HoughMade]

On BS34 carbs, the idle mixture adjustment is a fuel adjustment, not air.

 

[226dark]

stand corrected, thanks Hough

 

[HoughMade]

Not a problem- on the VM carbs, I think it's an air screw. In any event, out makes more rich, in makes more lean just like you said.

 

[JARichmond]

I should clarify, I suppose. I tightened it in order to reduce the fuel entering the combustion chamber.
What really confuses me is that I had a great run a few days earlier where my only complaint was that I had to adjust the idle. The next time I pulled out the bike it was popping so I enrichened both sides and eventually leaned out the left side because of the sooty spark plug. I haven't touched the mix screws since then, but am tempted to reset them both when I do a carb cleaning this coming weekend.
While I have the carbs off I'm probably going to replace the intake boots and get a new o-ring for the petcock because I had to temporarily replace it with an elastic band.

 

[domains]

those old cracked boots

 

[JARichmond]

Next issue:
I pulled apart the petcock in order to fix a stuck vacuum valve. Unfortunately, when disassembled the selector valve (the thing that points to ON, RES, PRI), the o-ring fell off and was too large to fit back in the recess. I have no problem ordering the part, but I am wondering what the part number for it is. Right now it's temporarily been replaced by an elastic band I found in a drawer, but it limits the movement of the petcock to just ON.

 

[drewpy]

Next issue:
I pulled apart the petcock in order to fix a stuck vacuum valve. Unfortunately, when disassembled the selector valve (the thing that points to ON, RES, PRI), the o-ring fell off and was too large to fit back in the recess. I have no problem ordering the part, but I am wondering what the part number for it is. Right now it's temporarily been replaced by an elastic band I found in a drawer, but it limits the movement of the petcock to just ON.

this is the part # for 2A2 model but I don;t think they changed them much

1J7-24535-00 body gasket (even though its an O ring)