Bonneville America Forums Forums Technical Forums Performance Mods Shimming vs jetting

Needles are taped and go through the main jet so if you shim the needle it is setting higer allowing the thinner portion of the needle to be in the orafice of the jet. Causing it to run richer through out the throttle range until the needle is removed completely from the jet opening then you are at what ever the jet is.
Having a larger jet will result in the same thing as it will allow more fuel through the space between the needle and the jet the difference comes in when you are at full throttle and the tip if the needle no longer effects the amount of fuel that can flow. In this case you will be running richer at full throttle than with a smaller jet and shimmed needles.