[Dwight Southerland]

Not all 4gc jets are flat across the inside. There were three different designs over the years - one was flat, one had a small 45 degree chamfer at the top and the third had a large 45 degree taper cut that extended half the distance of the jet body. All had different flow characteristics so it is imperative when tuning that the same style jets is used when changes are made. Qjet jets will fit, but you may have to experiment with sizes to get the correct fuel-air mix if you have references from one of the 4gc jet styles.