Put another carb on a 472CID,the problem now is its high idle and tendency to race, vacum lines look good,seems like the only way to slow it down is pull the trottle linkage back, tried a stronger spring and still wants to idle high,though it helped some, revs about 1000 rpm as opposed to a comfortable 650. Any ideas how to get this right?
- Thread starter DCM
- Start date
old
Well-known Member
- Location
- Camdenton Missouri
Vacuum lines look good but do you have e-ray vision??? Wave a propane torch around them but do not light it or spray carb cleaner around them. Small vacuum leak will cause that and you can not see that with your eyes
Skip nailed it.
Once the throttle shaft bores in the aluminum throttle casting become worn, you will not be able to reduce engine speed to specified idle due to air leakage between the shaft and the aluminum casting.
There are no bushings in the throttle casting. Years ago, it was possible to buy bushings and bore the plate to install bushings but I doubt that the folks that once sold the kits are still around.
I expect that you can still buy a new throttle casting but they were over $100 25 years ago.
Dean
Once the throttle shaft bores in the aluminum throttle casting become worn, you will not be able to reduce engine speed to specified idle due to air leakage between the shaft and the aluminum casting.
There are no bushings in the throttle casting. Years ago, it was possible to buy bushings and bore the plate to install bushings but I doubt that the folks that once sold the kits are still around.
I expect that you can still buy a new throttle casting but they were over $100 25 years ago.
Dean
Mike in Mn.
Member
Back the choke and idle screws way off, loosen the throttle plates, close every thing tight and then re-tighten the throttle plates to center them. Most all of them I have ever seen bind at idle so they won't slow way down. Also check the secondaries for closing. I was a GM Dealership mechanic back in the 70's, those q-jets all needed a two hour blueprint job when new to make them choke and run right, set correctly they actually worked pretty good.
A FOUR barrel Quadrajet... WHAT a concept!
SORRY, I just HAD to say that!
LIKELY, Dean and Skip got it right. Besides the loose throttle shaft bushings, look to see if there are holes drilled in the butterflies. This was done in certain low vacuum applications for idle quality, and if you are using it on a different engine, it could be a problem.
SORRY, I just HAD to say that!
LIKELY, Dean and Skip got it right. Besides the loose throttle shaft bushings, look to see if there are holes drilled in the butterflies. This was done in certain low vacuum applications for idle quality, and if you are using it on a different engine, it could be a problem.
Also if you have a vacuum advance distributor a lot had a port or other way to stop the vacuum to the advance at idle that would end up making a slower idle.
Lots of those from the mid to late seventies or 1980 were good working units. If not most could be massaged to work good.
Lots of those from the mid to late seventies or 1980 were good working units. If not most could be massaged to work good.
Allan in NE
Well-known Member
There are two idle adjustment screws on a quadrajet.
Check the fast idle screw on the passenger side of the carb down under the choke linkage. It's kind of a stinker to get to.
Also, make sure that fast idle cam is dropping off (down) when hot.
Allan
Check the fast idle screw on the passenger side of the carb down under the choke linkage. It's kind of a stinker to get to.
Also, make sure that fast idle cam is dropping off (down) when hot.
Allan
Anonymous-0
Well-known Member
a 472ci can leak substantially at the shafts before it's gonna much effect that volume.
base gasket, or loose base itself
base gasket, or loose base itself
Bryan inIowa
Member
I keep bushings on hand for Q jets .
BushogPapa
Well-known Member
See that the "Dash-Pot" on the throttle-shaft is allowing the throttle to return to Idle..
Also, that the choke is opening all the way, to take it of the high-idle cam..
Ron.
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