Too rich

The problem exists in all 3 carbs so it logical to to focus solely on the "choke" system. The High Speed needle/jet has nothing to do with anything !  It's a completely separate system that does not come into play until higher RPMs require it; as kawboy mentioned.

The Choke Fuel Pick-up tube:  The metering-jet in the end of the tube is pressed in and I have seen many many carbs that have a cracked/split tube  from the "stress of the press" !   I've seen tubes that are 'cracked half-way up their length and the crack is not always immediately evident due to the patena of the brass and or Fuel varnish.  A crack(s) in the tube(s) would not likely create or be the source of this particular issue.  

By the description of the problem, the culprit(s) would be related to the the "Choke Rod", and/or the Lifting Forks,  and/or the "Choke Plungers" and/or the Choke-plunger seat (at the bottom of the Plunger bore") .
The lifting-fork arms should NOT be squeezing the "Spools". The only contact the Arms should have is when Lifting the Choke Plunger and that should only be on the Spool flange. When the Choke is OFF, the Spools should turn/spin freely and the lifter arms should be midway on the spool.  Not touching the spool, at all !   Otherwise you'll have resistance to closing. 
These Plunger seals are questionable, which is why they were replaced.
 
 
 
 
Lifting forks with adequate spacing to Spool:

 
 
Ensure the choke lever has full travel up and down but specifically down (Closed)  The Spools should also spin freely and move up/down freely on the plunger shaft ( about 2mm). When the plungers are in the Closed position the Lifting forks should not be in contact with the Spools !
Misaligned lifters can create a closing issue.  NOTE:  There is NO up/down orientation.  They are made symmetrical.  The misalignment can be from an asymmetrical point on the screw and/or the Point of the screw finding its "home" in a previous dimple in the choke-rod.  The "arms' on the lifting forks can be bent to the correct position very easily as the material is fairly soft.
 
 
If the Seat(s) (in the bottom of the plunger well)  has any nicks/dings they will  leak.  All 3 at the same time, you may ask ?   One can only speculate as there is no detailed history of how the carbs (bike) had been stored or serviced. over it's 40ish years.  Old fuel, fuel additives, dirt/rust from the tank prior to the addition of an in-line filter ?  These conditions can cause pitting of the choke plunger seat, as aluminum can be sensitive in this regard.

No mention of,  so I'll add this:  Flush Out the "Mixing-Air Ports !   If they are blocked or restricted further (in addition to their metering jets) an extremely rich mixture will result. 

 Ya, I know !  I should have Started with and Ended with this, alone ! 

......or simply those nocturnal "Shop Gremlins" that are notorious for "F'n with things when we're sleeping !



 

Right on !!! The original choke plungers on mine look as bad or worse than those in the pics. This bike sat for around 20 years before I bought it, going by the license plate. Imagine the springs pushing the plungers down for that long without moving. When I first rebuilt these carbs I decided not to use the ones from the aftermarket kit I bought for 2 reasons, one they didn't have the little tit that goes down the choke orifice, two they just didn't seem to fit that well. When I put them in I had the same issue as the originals, too much fuel. Now I see why. The aftermarket plungers were binding big time in the plunger retaining nut, I doubt they were seating. So I "turned" them down with some 1000 grit sandpaper in the drill press, now they move freely. I will adjust the lifters carefully. Carbs will go on tomorrow and see what happens ? 

Hoping for good results!
Keep us posted..

I learn from everyone that posts their experiences...

d

 

Our friend hasn't answered yet, but I have a question. My A1 '79 bike seems rich at idle because I always find the spark plugs black with soot.
Let's take it one step at a time.
The bike runs better since I installed NGK BP6ES spark plugs instead of BR8s. With the resistor caps and BRs, it had very little spark.
The exhaust, hovewer, is always very dirty at the bottom, and when it's running, the bike smells a lot like exhaust.
It seems to me that the motorbike consumes a lot of fuel.
I haven't serviced the carburetors yet; I'm waiting for the floats from Scotch.
I checked the starter valve mechanism carefully even though I didn't disassemble them and it seems to have the right tolerances.
Do the mixture screws adjust air or fuel? How much should they be set to as a starting point?

baz wrote:

Our friend hasn't answered yet, but I have a question. My A1 '79 bike seems rich at idle because I always find the spark plugs black with soot.
Let's take it one step at a time.
The bike runs better since I installed NGK BP6ES spark plugs instead of BR8s. With the resistor caps and BRs, it had very little spark.
The exhaust, hovewer, is always very dirty at the bottom, and when it's running, the bike smells a lot like exhaust.
It seems to me that the motorbike consumes a lot of fuel.
I haven't serviced the carburetors yet; I'm waiting for the floats from Scotch.
I checked the starter valve mechanism carefully even though I didn't disassemble them and it seems to have the right tolerances.
Do the mixture screws adjust air or fuel? How much should they be set to as a starting point?
 

You can download factory service manuals from this link.  Scroll to page bottom. Most find 3 to 3.25 out works best if stock airbox is used.

hi Baz.  Your Floats are ready to mail but I need your Phone # for the shipping info.  
P.M. me