Old Britts – Amal Concentrics, How They Work and Tuning
Download the complete PDF version using the green download button at the top right of this page for an Old Britts technical article explaining Amal Concentric carburettor operation and tuning. Based on a Norton Triumph shop poster from the 1970s, this guide adds useful comments and part numbers while showing how the carburettor meters fuel across different throttle openings. It is a clear reference for understanding the main jet, pilot circuit, throttle cutaway, needle position and float chamber behavior.
The article begins with a numbered cutaway drawing of the Amal Concentric and a parts list identifying items such as the throttle valve, jet needle, float, needle jet, main jet, pilot air screw, tickler and drain plug. It then gives the recommended tuning order: main jet, pilot circuit, throttle cutaway, needle position and a final pilot readjustment, all with the engine fully warmed and the motorcycle in normal running trim.
Later sections illustrate how the carburettor works at closed throttle, one-eighth to one-quarter throttle, one-quarter to three-quarters throttle and three-quarters to full throttle. Each stage explains which circuit controls mixture at that point and what tuning symptoms to look for. The final pages cover float chamber operation and float level guidance, including the stated fuel level range of .170" to .240" below the top edge of the float bowl and a practical method for estimating the float position.
Contents Include
- Amal Concentric carburettor cutaway and numbered parts list
- Recommended tuning order for the major carburettor circuits
- Pilot circuit adjustment at idle and low throttle
- Throttle cutaway effect from one-eighth to one-quarter throttle
- Needle position tuning through the midrange
- Main jet behavior at three-quarters to full throttle
- Symptoms of rich and lean mixture settings
- Float chamber fuel flow explanation
- Float level guidance and adjustment notes
- Part numbers for key Amal Concentric components
