Drilling Holes In Carb Throttle Plate Blades

What happens is you have enough cam timing (evidently) so you have to open the throttle blades up to get an acceptable idle.

When you do that you uncover too much of the T slot and it will pull fuel from the T slots at idle and it gets nasty rich.

You also have little to no adjustment on the idle mixture screws.

The holes in the throttle blades are a controlled (depending on the size of the holes) air leak.

That air leak allows you to close the throttle blades and still get a reasonable idle speed, except when the holes are the right size you will have most of the T slots covered.

That’s it in a nutshell.

How do you know if you need them?

First you need to answer post 6.

If your timing is where it should be, and you have little or no adjustment on the idle mixture screws AND your carb doesn’t have an adjustable idle bleed built in then you need some holes.

Also, if the idle is where you want it but it’s too rich then take the carb off and flip it over and look at how much T slot is exposed.

If you are somewhere between the T slot making a square with the throttle blade and no mouth than about .080 exposed you may just need to change the idle air bleed to clean it up.

If it’s more than that you need to get more idle air to allow you to close the throttle blades and get off the T slot at idle.