Hitchcocks Forum

Now, I really should know this, but when you start to tune in Amal mark one concentric's idle speed, what's the best starting point for the throttle stop and the air screw?

Air screw 1 to 1.5 turns out. Throttle stop is the best (lowest) position consistent with slowest running with the air screw in the above range.
REgards, Mark

Also, consider getting a Gunson Colortune. With the Concentric it sometimes helps to set the tickover mixture a shade on the rich side to ensure the tickover is reliable even before the engine has fully warmed up, and to help avoid "fluffing" when you open the throttle.

Latest news is that the kick start return spring has broken,calling a temporary halt to proceedings.
I have a color tune, but they don't see m to work as well as I remember; modern fuels, some say.

Tuning with the throttle stop screw and air screw is tuning for tickover. To tune a Mk 1 Concentric for tickover the best initial set-up (with a warm engine) is to set the throttle stop screw to give a fast tickover – whatever position that takes. Then turn the air screw either way to obtain as fast an engine speed as possible. Using the throttle stop screw reduce the tickover to a nice steady speed. Repeat this sequence, again using the air screw to achieve fastest possible engine speed – turning it in either direction to achieve this. Then finally reduce engine speed to a steady tickover with the throttle stop. This may give you a final setting on the air screw of approx 1 ½ turns out, it may not, but that in itself isn’t of any critical importance.

The only thing I might add to that is that I'd recommend you err very slightly on the rich side of perfect. The reason is that the mixture coming from an Amal at tickover can be quite "splashy" - you can see that with a Colortune - rich in one cycle, weak in the next. You will probably get a more reliable tickover if you have the mixture perhaps 1/8th to 1/4 turn rich on the air screw. It also helps reduce any "fluffing" when you take it off idle.

Oh, damn, I've already written that above. Sorry! Going senile, obviously.......