Thread: carb spacers

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i picked up a 1/2 spead bore phenolic spacer on ebay along with 2 square bore holley style spacers.
all came ok but i went to put the one spacer under my quadrajet and found that the big bores are about 3/16 too small and prevent the butterflys from opening.
did gm make 2 sizes of bores in a quadrajet?? or could this spacer be for something else. everything else lines up re bolt holes and small bores.
live and learn didnt spend a lot at least and i think i can pawn off the other spacers anyways
has anyone attempted to cut one of these spacers? as i took a carb gasket and scribed the right size oval hole and am going to attempt to cut the hole to match the gasket tomorrow with a very fine blade on my jig saw.
i tried in the past to make a spacer from wood but did not seem to have good luck with it so i found these. this cut will be easier as is only one large oval.

ive cut one before, you will be fine, whats the worse thing that can happen, it already does'nt work!

yeah i dont have much to lose

Phenolic is nothing but cardboard and a resin pressed into a flat piece of stock. You can easily cut the stuff with a wood boring bit called a Forstner bit as long as you are careful. Tightly clamp your spacer between two pieces of fairly hard wood - the top piece being pre-drilled as a jig then drill through the spacer and bottom as one piece. You should use a drill press to minimize any bottom side of the spacer tearout.

Any fairly good hardware store has these bits but cheaper Chinese made ones are found places like here:

http://www.mlcswoodworking.com/order.../forstinx.html

or here
http://www.rockler.com/CategoryView.cfm?Cat_ID=531

or cheapest, here:
http://da.harborfreight.com/cpisearc...tner&Submit=Go

put a fine steel blade in the jigsaw and cut the large side out in a oval as per the gasket shape, darned stuff is hard but it cut then shaped and smoothed it out pefectly with a bastard file and then a drum sander bit in the drill press. looks like it will work fine.

Originally Posted by canadianal

.... did gm make 2 sizes of bores in a quadrajet??

Hey Canadi or do people call you anal for short? Sorry, I couldn't resist. I tried deleting it after I read it but for some reason my back space isn't working, hopefully your back space is.
Yes, there are two sizes of Quads in bore sizes and even more sizes via spring and needle adjustments.

If memory serves me right, there is a 750 and a 850 cfm. The difference is in the front two ventury bore sizes. If you have the two carbs next to each other, it is easy to tell them apart due to the shoulder size inside the venturies. The back space remians the same.
Yours truly, Bob

very funny never thought about it that way wheres your mind
is it the inner or the actual butterfly portion that is larger, the secondary (big side) of the carb butterflys were bigger than the carb spacer.
its modified and on the car now. i dont think it was the phenolic stiff i think its a resin plastic it cut and sanded awful nice

Originally Posted by canadianal

very funny never thought about it that way wheres your mind

Glad you can take it.

Originally Posted by canadianal

is it the inner or the actual butterfly portion that is larger, the secondary (big side) of the carb butterflys were bigger than the carb spacer.

K, I do believe the primary venturies and butterflies are larger on the 850, not the rear. Having said that, you can enlarge or downsize the cfm with different cams and needles on the rear, all the way down to a 550.
They are actually a really nice carb.