Cliff's Quadrajet Parts and Rebuild Kits
Quadrajet Problem Solving => Dialing in your rebuilt Quadrajet carburetor => Topic started by: J.Peter on July 25, 2024, 11:41:53 AM
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I need help with my Quadrajet on my big block 70 Vette.
My carb is not the original part.
I need to drill the hole in the drivers side primary throttle bore for a ported vacuum advance setup. The outer fitting is already there but it is not drilled through to the throttle bore.
I know the hole should be slightly above the throttle blade - but how far above and what diameter should it be?
Even a photo with no dimensions would be very helpful.
Thanks
J.Peter
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You'll need a donor baseplate to get the exact measurement. Make sure you are on the drivers side as some carbs had a higher location on the passengers side for ported vacuum which is meant for EGR.
I use a very sharp punch to make a starting point for the drill bit. Using a pin vise to hold the bit helps as it lessens the angle some.
The factory actually used a slot instead of a hole so that there would be more area uncovered. Since making a "slot" is difficult I'll drill a small hole and very carefully work the bit back and forth to widen it as much as possible.
I use a .046" drill bit, USA made. If you try to drill that small of a hole with a Chinese bit good luck, they break if you stare at them too long!......
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Thanks for the reply,
I like your idea about the slot - I will use a small Dremel bit.
Thanks also for writing that lovely rebuild guide book.
Last fall when I took this carb apart I added some threaded idle tubes - they work nice.
J.Peter