Chevy Quadrajet
#1
06-14-02, 02:14 PM
Chevy Quadrajet
I have just replaced the intake manifold and carberator on my 86 chev pickup, the engine is a 78. The carb and intake is used but i know the vehicle it came from it was working fine then, but it has been sitting for 2 years. I put them on my engine got the truck running but the idle is really high, the idle screw is backed right off and its running rich. I tryed adjusting the jets but cant seem to leanit out enough. I have checked for vacuum leaks but didnt find any.
Is my carb due to be rebuilt and how are those quadrajets to rebuild?
The carb is on a 1978 chevy 350 with a 700r4 behind it.
When i take the vacuum line off the vacuum advance and plug the line it seems to run better.
Is my carb due to be rebuilt and how are those quadrajets to rebuild?
The carb is on a 1978 chevy 350 with a 700r4 behind it.
When i take the vacuum line off the vacuum advance and plug the line it seems to run better.
#2
06-15-02, 12:09 AM
I suggest the Q-jet book written by Doug Roe or the factory shop manual to guide you through the rebuild. They're a little daunting to the first time DIY rebuilder....
Assume that the first guy that owned the carb/did the rebuild did it totally wrong. Completely rebuild it yourself, go through it completely, starting with factory settings and going from there.
Also replace the vacuum advance at the same time with an OE quality replacement.
That being said, while a 1978 carburetor will work on virtually anything, there's zero merit to using it on a 1986 truck. Rochester changed carbs year to year for a reason. Secure the right core # for your application and rebuild that one. The truck will run a ton better in the long run.
Assume that the first guy that owned the carb/did the rebuild did it totally wrong. Completely rebuild it yourself, go through it completely, starting with factory settings and going from there.
Also replace the vacuum advance at the same time with an OE quality replacement.
That being said, while a 1978 carburetor will work on virtually anything, there's zero merit to using it on a 1986 truck. Rochester changed carbs year to year for a reason. Secure the right core # for your application and rebuild that one. The truck will run a ton better in the long run.
#3
06-16-02, 03:16 AM
Agree w/ Joe. The book he mentioned is Rochester Carburetors by Doug Roe. Lots of great info there, well worth the $12.57 price.
For what it's worth, it sounds like your well plugs are leaking. You can seal them w/ epoxy. The procedure is covered in detail in the book mentioned above.
For what it's worth, it sounds like your well plugs are leaking. You can seal them w/ epoxy. The procedure is covered in detail in the book mentioned above.
#4
06-16-02, 07:05 AM
Super Moderator
In the meantime
Joe_F and knuckles are probably right, but there are a couple of things you can check.
The screws you are probably adjusting are the idle mixture screws at the front of the carb and only affect idle speed operation.
If the engine is idling too fast and the idle speed screw on the drivers side of the carb is backed off all the way it is probably the fast idle cam controlling the speed. The fast idle setting is on the passenger side of the carb and is controlled by the choke. You could try setting the choke leaner. If the choke opens properly as the engine warms up, you can then set the adjustment screw to set the fast idle speed. It is on the choke side of the carb. You would then have the speed set when the choke is on by the fast idle cam and when the choke is fully open the idle speed screw on the drivers side takes over.
Also, when you take the vacuum line off the vacuum advance and it runs better, try plugging the end of the hose with your finger. If the idle changes when you plug it then it most likely is running rich but if there is not much change then it could be a timing issue.
The screws you are probably adjusting are the idle mixture screws at the front of the carb and only affect idle speed operation.
If the engine is idling too fast and the idle speed screw on the drivers side of the carb is backed off all the way it is probably the fast idle cam controlling the speed. The fast idle setting is on the passenger side of the carb and is controlled by the choke. You could try setting the choke leaner. If the choke opens properly as the engine warms up, you can then set the adjustment screw to set the fast idle speed. It is on the choke side of the carb. You would then have the speed set when the choke is on by the fast idle cam and when the choke is fully open the idle speed screw on the drivers side takes over.
Also, when you take the vacuum line off the vacuum advance and it runs better, try plugging the end of the hose with your finger. If the idle changes when you plug it then it most likely is running rich but if there is not much change then it could be a timing issue.
