Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

Setting Up and Adjusting Idle

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omaha:
   I think I would do this; check for a vac leak that might be a vacuum hose, it kinda sounds like you problem..Also, if the idle mixture needles are not seating all the way, the spring on them may be at coil bind. You may need to trim a coil or two from them. You shoukd be able to kill the engine with the turning in of the idle screws. Of course, you wont get a super smooth idle with  the cam you have but it should be close to a factory performance cam, pretty smooth in the case of an olds. As far as the gasket goes, yes this may have a vacuum leak but unless you can check for a leak....in the old days, I used to use an unlit propane torch to check for leaks but everyone seem to think it is dangerous. I guess maybe but the only other way I know of is some type of spray. Another guy I know says he sprays water to check for leaks. I have never tried it but who knows. Dont forget to check the timing and you should have 12 at idle, (vac. adv. disconecttd.) Try 14 degrees and see if it helps, if not, put it back. check plug wires too, firing order and connections. If the spacer is good quality, it should work. But, you might try it without the spacer just to see if it makes a difference.

defiant1:
Ok - update:

- Can't install carb without spacer, due to throttle linkage hitting intake. So could not attempt that setup.
- Installed different gaskets (thicker base gasket).
- 10* at 1100 rpm for timing based on what the manual is telling me to set it at.  
- Vacuum gauge read 10.5" at 700-750 rpm.  18 inches @ 2000 rpm.  No idea what that means in the large scheme of things.
- Idle mixtures screws DO now affect rpm when screwed in, whereas before they did not.  So I am gaining there, I think.

I am going to do a compression test on the cylinders and see what I come up with.

Forgot to add:  I used a stronger power piston spring.  It was the same length as the factory spring, but there were more coils (if that makes any sense), basically a stronger spring.  Should I put the factory or replacement equivalent in and see if that helps with the idle.  Of course this is assuming the vacuum numbers listed above are ok.

d1

jamesF:
Make sure the flaps are closing all the way. Work them a little and push them closed as you run it to see if they are not fitting tight or closing 100%.

defiant1:
Not sure what you mean by moving the flaps or attempting to move them.  Can you elaborate?  Side to side movement of throttles shaft??

Well I did the following this afternoon:

BTW: I have the Petronix III unit with flamethrower coil.  I ran this setup with my former 2BBL/intake (same motor w/o head work) at 10* BTDC at 1100 rpm (dist. vacuum capped off).

I just finished my compression test, ran motor to operating temp and took readings:

#1 - 159
#3 - 155
#5 - 155
#7 - 162
#2 - 157
#4 - 159
#6 - 163
#8 - 160

Not too bad for a 40 yr motor with no work done to the bottom end.
I also checked the plugs and the #1 plug was the worst looking-had a black coat on the ceramic.  The remaining plugs had a light to dark brown ceramic coating.  Nothing was covered in soot.

When motor was running I got brave and squirted starting fluid around base of carb.  No noticeable difference in rpm occurred.

The local mechanic thought the vacuum was pulling from w/in the carb itself.  If that is the case I have no idea what circuit inside the carb controls that.  BTW I had every vacuum port plugged with the exception of the PVC and the power brake hose which I used to hook up my gauge.

I noticed this time around my idle Hg reading at 750 was a steady 11".

I thought I had fixed my idle mixture screw problem, but I screwed them in all the way and the idle did not change (well maybe 50 rpm--but it should have  made a noticeable difference).

New items:
4BBL Q-jet
Cam: custom grind 217/224 @.050
Edelbrock Performer intake

I am open to suggestions.

d1

defiant1:
Ok- trying to eliminate things that could cause problem.  I took a skinny screwdriver and placed it in the vent tube to ensure the power piston goes up and down (motor off). 

With motor on, I did the same thing and the power piston is fully seated.  So the light blue spring I am using is not affecting the idle circuit from what I can tell.

Adjusting the idle mixture screws in or out does little to nothing to the RPM.

I am out of ideas.

- 10.5" Hg at 750 rpm - not sure if that is good or bad
- Idle does not improve when I cup my hand over primaries
- Sprayed starting fluid around carb and rpm did not increase

What else can keep the idle mixture screws from doing their job???  ???

d1

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