pauldridge wrote:After being unable to resolve erratic idle speed and other issues on my '72 Combat Commando, I decided to spring for a pair of the new, "improved" Amals.
Once warmed up, these new Amals are perfect.. stable idle, strong powerband right to redline, etc.
Good, settings are clearly correct/ close enough.
However, one nagging issue persists:
I think you mean a "new dynamic exists".
with the old Amals, I could ALWAYS light off the Combat with a single kick
and no choke,
That is bad.
But my new installation seems to want 1/2 or more choke on startup,
That is good.
and then after tickling, will still fire on first kick, but then runs 2-3 seconds then dies.
Insufficient tickling/insufficient choke, or pilots too small (possibly).
Back to a second tickle, same trick..
runs a few seconds and dies. Usually the 3rd attempt is a charm and I am able to keep the bike running.
A little heat from the first couple of attempts has warmed the intake manifolds sufficiently to reduce Condensational Losses to a point where the bike will now run. More choke if possible, and keep throttle as closed as possible.
Still, it runs rough for a minute or so,
That is ok, add some more choke if possible, the engine is currently lean due to the fuel falling out of suspension after contact with the cold manifold walls(aka Condensational Losses).
whereas before I could literally launch off immediately
That is bad. Too rich.
For some reason, it just seems as though initially the carbs aren't getting enough fuel.
No, the engine is not getting enough fuel. Your new carbs are not running stupidly rich like your old flogged out ones were, and you need to compensate for the condensational losses appropriately.
Very unlikely that the fuel flow to the carbs themselves is in any way varying hot or cold.
In conjunction with the new Amals, I also purchased a nice one-piece swaged-fitting transparent fuel line and I can clearly see plenty of fuel in both lines.
Of course, fuel flow almost certainly has nothing to with it.
After a short ride, the Norton is back to its old health,
That is good, carb settings (outside of choke/enrichner) are only relevant to fully hot running, and yours sound close.
and even after a 2-3 hour rest, will fire right up on first kick, no choke, just like always.
Residual manifold heat, not some "extra special engine or carbs" ( I say that jokingly as over the years so many people have tried to tell me their engine is a "really good one", as it doesn't need choke from cold. Apparently it never occurred to them their vehicle was simply too rich on the low speed).
I am baffled as to what might be the problem.
There is no problem, as such.
If the bike really exhibits extreme symptoms of the ticklers and choke being unable to overcome the COMPLETELY NORMAL dynamic of Condensational Losses (which your old carbs were masking, as they were running far too rich, and which is exactly why we have enrichers and chokes, not because cold engines need more fuel, but rather because, in simple terms, they need the same fuel and are simply not getting it), then the next size pilot is for you, as you may be slightly too lean.
Hope that helps.