Re: Metering rod for Carter WDO 531 S

Posted by DavidPackard On 2020/10/7 17:01:14

JosefClipper47;
Metering rod part number 75-621 is from the 643S & SA parts list. It is the Lean 2 (meaning two steps lean from standard) configuration. The diameter geometry is 0.0685, 0.0625, 0.056, those would be the diameter of the rod in inches . . . measured at the three steps.

The 75-538 / 75-616 metering rod geometry is 0.064, 0.057, 0.054

Both the 531 and 643 share the same main jet size of 0.0955 inch diameter.

Both carburetors appear to have the same venturi sizing, therefore you can compute the gasoline flow area and do a direct comparison of the two configurations.

The Carter parts lists will list the standard metering rod, and then two additional rods that would produce a leaner mixtures. I've always associated the lean metering rods for cars that are operating at altitude. If your car is operating above 5000 feet the two step lean maybe suitable. At any rate it looks like a sometime in the past your carburetor was adjusted for altitude operation . . . or someone lost the standard metering rods.

dp