G'day Brad, Have you owned an English bike before. More to the point, are you really familiar with Mk 1 Amal carbs.
If you are a reasonably competent mechanic with mild experience on Japanese bikes, this won't help you now. Sorry.
Lesson # 1.. Amal Mk 1 carbs were made of a substance (pot metal) that in most cases, wears very quickly.
Hence the Slide (throttle valve) can become very loose in its fit to the body. Allowing extra air into the throat,
resulting in tuning problems.
Lesson # 2.. Read the threads on cleaning Amal carbs. In particular, the Idle jet passage, and, Ethanol fuel problems.
OK, Lets now assume that you've read these and the carbs ARE clean. And the Slides are tight, and the "O" rings on
the adjustment screws are in good condition.
As Josh asked.. Do you have Air slides (choke slides) still fitted to your carbs. If so do you use them.
It sounds as though your carbs are lean at idle. That is, it runs OK untill it uses up the fuel created by tickling the carbs.
An easy test is to remove the air filter, start the bike, and hold two fingers over the mouth of the carbies, this will "choke" them.
OR.. leave the Air slides partially closed.
OR.. Start the bike, it's now idling at 1500, when it starts to run down, press the ticklers. (add some fuel).
If it helps then you know you are lean. This could be caused by a partially blocked idle circuit. And or, the wrong Mixture screw setting.
If the bike won't start at all, or starts but won't rev as it usually does with out the extra choke, then you are probably rich.
Check the slides for excessive wear, and check the four O rings on the Idle and Mixture screws.
Also check the eight mounting bolts on manifold and carbs. Not too tight, as they can distort and give an air leak.
Lesson # 3.. It might be electrical.
Have fun.
