Quadrajet question

In order to open the hole in the vacuum break, you will need items called a "pin vise" and "wire drills". Do a web search and you should find the wire drills. Can't recall if they are available in .001" increments, but I do know they are available in .015", .020" .025" and .030" sizes as I have some of them.
You may also be able to get a pin vise and wire drills at a model or hobby shop.

Good Luck,
Scott

 

Well thats a problem. 1-1/16 is what i come up with. How do you adjust it?

 

LOL!! Sorry!!! I forgot to mention thatyou measure when you have the secondaries all the way open!!! ou:

 

Quick answers, then gotta go...

No, revving the engine in the garage probably won't be enough to get the secondary air valves to open, unless you want to wait for 9000 rpm!

Enlarging the hole (orifice) in the diaphragm will allow the air valves to open more quickly. But don't mess with it until you've played with spring tension to no avail.

Yes, drill bits come that small, but try the easy stuff first!

Devon

 

ARGH!!! So much going on here!!! :eek2: (just kidding...)
Reving in Park will tell you nothing. At best, the secondaries may open 1/4" in Park. Since there is no load on the engine, airflow through the carb is still minimal, and vacuum is still high, keeping the choke pull off/vacuum break pulled in. Under real load at WOT vacuum drops to near 0.
Yes, enlarging the hole in the choke pull off/vacuum break lets vacuum in faster, but that is not an issue. The issue is how fast it can it dump vacuum when engine vacuum goes away.
Hanger hole height. The secondary rod hanger has a letter stamped on it. The lower the letter, the higher the hole (and the sooner the secondary rods lift, admitting fuel into the secondary curcuit.) You can bend the hanger, or do it the "right way" and get a lower letter hanger. Either way, this is a very minimal, after everything else is right, kind of adjustment.
If you bogged with the choke pull off/vacuum break disconnected and plugged, there is your starting point. Adjust the spring.

 

Guys,
I reduced the spring tension about a quarter turn. Any more than that and the secondaries will not close when pushed wide open I notice a difference however its not as significant as when the v/b is disconnected. With the v/b plugged its as if the power comes on sooner, it also makes that cool Quadrajet sound.
The way I have been road testing it is revving it up to about 2000 and punching it to see how it responds. I figure with 2.73 gears testing at lower rpms it futile.
About the bog, I should clarify something, it only bogs when the v/b is disconnected and I punch it at very low rpms (maybe a 10mph roll). From what Im hearing that is to be expected.
The letter on the hanger rod looks like B/P.
No doubt Im making progress but it seems like those secondaries should open up a little sooner, but not quite as fast as when the v/b is disconnected. Do you think it has something to do with the fact that this carb is for an auto car? Whats the difference?

 

Not to be expected and not ideal. You are just confusing the situation by going back and forth between vacuum beark connected/disconnected before you get the spring right.
At wide open throttle you should be controlling the secondaries entirely and exclusively with the spring. It sounds like your spring is too loose now. You should be able to go to WOT from any rpm or any roll with no bog, vacuum break disconnected. After you get that right, THEN reconnect the vacuum break, and enlarge the hole as needed to have WOT performance as good as when the vacuum break is totally disconnected. The situation you want is that at WOT the vacuum break dumps faster than, or at least as fast as, the spring is willing to let the secondaries open. Then at say 3/4 throttle, when vacuum does not go entirely away, the vacuum break will come into play and slow down the secondaries.

 

I agree, it's time to enlarge the vacuum break orifice slightly. This will allow the diaphragm to relax more quickly, thus allowing the air valves to open more quickly. Just take it a tiny bit at a time.

Devon

 

Yes, your vacuum break is too restrictive, as proven by the fact that everything goes to pot everytime you reconnect it, but PLEASE, get the spring right first!!! One thing at a time!

 

Ok, got it! Adjusted the spring tension so no more bog. Ended up being about 1/8 turn from where it was originally. Still pleny of power, cool sound still present. One observation I made is the spring tension is less when the engine warm so I made all the adjustment when warm.
Now for enlarging the orafice. Searched the web for "wire drill" and "pin vise" and the only thing I came up with is #61-#80 which according to my calculations is still too big (.0390-.0135). Can someone point me in the right direction?
Beautiful day today so I'm going for a ride (v/b disconnected for now) :grin:

 

Good question, Matt! I don't see anything listed that's smaller than #80, I'll keep checking.

Devon

 

Just remembered what I used years ago...a sewing needle. Because it has a taper from a fine point I just used pliers to progressively push it into the orifice further and further until I got the diaphragm to respond the way I wanted. Unfortunately I can't say what the diameter was when all was said & done, but it did the trick!

FYI, looks like the smallest metric drill available is 0.25mm (about 0.010") and they go up in 0.05mm increments from there.

Devon

 

Ok, now we are getting away from "doing it right," but truth is, it will probably work fine with spring control only. I ran for years with no vacuum break at all, and only a correctly tensioned spring. Granted, outside of dealing with an occasional idoit who didn't know who to merge on an interstate on ramp, my car only openned the secondaries from a standing start with a finish line 1320 feet away. So "3/4" throttle was not an issue. Keep hunting, and get the smallest drill bits you can find. Do you have a good hobby shop where you live? Model railroaders are probably the biggest users of tiny drill bits. A correctly-tensioned spring and too big vacuum break orifice is way better than a correctly-tensioned spring and too smal orifice.

 

Must be something going on with the hobby shops in my neck of the woods. I called 5 and all 5 had disconnected numbers. I'm in no rush and will wait until I eventually find the right size bit.
Looks like metric is the way to go .05mm incriments are almost perfect (0.001968498 according to my calculations).
Just came back from a 75 mile cruise and all went well, had to cut it short because it looked like rain and I haven't installed wipers yet.
Thanks everyone for your help and especially your patience.
Matt