I have a latter throttle body with the secondary spring that I would like to add the fitting to. A previous thread described more than one location(on center with the boss and above center). Could someone please make an accurate measurement above the closed throttle plate for the through hole and the actual size of the hole on an original '73 unit?
Much appreciated,
ScooterD

Its the boss that already there. Drill a 3.5mm bit 'bout 1/4" into it, then the tinyest bit you can find for the thruhole. Tap in a short piece of tube steel thats 'bout 4mm for the port.

here, look

Measurement is 37.5mm as shown in the picture. Note that the hole doesn't end up being centered on the boss - but I checked some throttle bodies that had it from the factory and this is where the advance port was located.

The hole that goes all the way thorough into the throttle body is very small - I don't remember how big, but probably around .040" dia. So first drill the small hole, and then use a larger drill sized for the tubing that you will insert into it. The larger hole goes deep enough to hold the inserted tube. 2nd picture shows a view inside the hole I drilled and you can see the smaller hole that makes it through to the throttle body.

Hope that helps.

Demick

Still looking for a definitive answer. I only have one chance at drilling the hole in the right place. Doesn't anybody have an original '73 throttle body they could measure?
Thanks,
ScooterD

Sorry,
Demick posted the response as I was writing the last post looking for an answer.
Thanks Demick!

my extra 73 throttle body so you can see its centered on the boss. The thru hole is TINY and right above the throttle valve.