Punch out or cut a circular piece of 2-3 mm cork sheeting that will be a slip in fit in the clear plastic cap baffle. Make sure it doesnt go higher so it still retains an air gap when you put the baffle back in the cap.
Pierce a 1- 1.5 mm hole( or same size as the cap vent hole) halfway between the centre and the rim, and place the cork in the baffle recess, then fit the baffle in the cap.
The cork will absorb some fuel and the offset hole should also slow it.
Not perfect always,but Ive not found a much better way.
Another option is to make a vented cap using a small inline fuel filter incorperated into the cap, or an overflow system. Both will work,but at the cost of orginalty. Use the Filtered caps for mowing and original cap for display?
Try the cork and see if it works for you first.
