3 hours ago
Hi
The attached book has useful information including the needle profiles. As a starting point the needle must be chosen from a range designed for the size of jet used e.g. 0.090 inch. Needle dimensions are critical to fractions of a thou especially around the idle end, so unless you are certain that the jet and needle have not worn against each other (they are not supposed to touch) I recommend you start with new ones.
For what it's worth, I run an SU H1 from a Morris 8 Series E, which is a 1 1/8 inch carb with a weighted piston. The chosen needle was GG, and road testing with a wideband oxygen sensor in the downpipe has shown that it is pretty well spot on for Air/Fuel ratio throughout the load and RPM range. The sensor and display are not cheap, but I use them on other cars. A threaded boss has to be welded on to the downpipe and can be fitted with a blanking plug when the sensor is not required. Thoroughly recommended if you are serious about tuning, and much superior to any other method I have tried. The readout is pretty well instantaneous whilst driving.
The attached book has useful information including the needle profiles. As a starting point the needle must be chosen from a range designed for the size of jet used e.g. 0.090 inch. Needle dimensions are critical to fractions of a thou especially around the idle end, so unless you are certain that the jet and needle have not worn against each other (they are not supposed to touch) I recommend you start with new ones.
For what it's worth, I run an SU H1 from a Morris 8 Series E, which is a 1 1/8 inch carb with a weighted piston. The chosen needle was GG, and road testing with a wideband oxygen sensor in the downpipe has shown that it is pretty well spot on for Air/Fuel ratio throughout the load and RPM range. The sensor and display are not cheap, but I use them on other cars. A threaded boss has to be welded on to the downpipe and can be fitted with a blanking plug when the sensor is not required. Thoroughly recommended if you are serious about tuning, and much superior to any other method I have tried. The readout is pretty well instantaneous whilst driving.