I picked up a nice original single carb 750cc '73 Tiger today. The bike starts easily and runs great at all throttle openings but won't idle well. The bike runs ragged and uneven at idle. Idle speed is roughly 1000 rpm.
The 930 AMAL was replaced about 10 years ago and maybe has a couple thousand miles on it. It idles best with the mix screw turned out about one quarter (1/4) turn from seated.
With needing to be 1/4turn from seated for best idle, it sounds like blockage to me too. Turning the mixture screw inward cuts the air supply off to the idle circuit, so either the fuel is restricted or there's an air leak elsewhere (manifold, etc).
I hear the US gasoline has an alcohol content. That won't be good news for carburetors, especially zinc based ones. I speculate that even the small amount of alcohol in the fuel will be attracting moisture. I run alky in the dragbike so I see the damage it can do. The carbs get drained EVERY time on that bike. So I just wonder how the Amals are they holding up to the US fuel?
@ Excalibur They are holding up just fine. Bored and sleeved to correct wear problems, an annual PROPER cleaning and a bit of spring time general maintenance works miracles. I have access to aviation gas and I quit using it as it plugged up the idle jet all the time. I don't know how planes run on it. PS Bless you for keeping Triumph in the records book.
1968 T120R 1972 T120RV Any advice given is without a warranty expressed or implied.