i don't think you need to be drillin on your carb. I have had several o.s. .40 la motors, and in my opinion they are an excellant little motor, for a good idle, make sure you have a GOOD glow plug. they do also like to have the air bleed screw set just right, the manual will give you step by step instructions on how to do this, and when making adjustments remember,,a little bit at a time. make sure your needle is set right ,,1 1/2 turns open from closed , then tune till peak rpm is reached, then back the needle off 20-30 degrees.