Question about Q Jet Tuning

[Julien Abrahams]

Could be, but what I've read, if you have vacuum leaks past the throttle shafts, the primary shaft is the one that gets "resleeved", as the primary side is only used for idling and the secondary side only for  high speed conditions and (almost) full throttle acceleration. So I don't think that a vacuum leak of the secondaries can cause bad idling.
It would not hurt to have a look at the gaskets of the carb (between throttle body and intake manifold, between the throttle body and the float bowl, and the one between the airhorn and the float bowl. If one (or more) of these are bad, it can lead to vacuum leaks and bad idle in turn.   

[Hankk17]

Since we're on the subject of quadrajets I'll add my question to the mix.  I've managed to get my quadrajet to stop idling so rough and it's nearly as responsive as I need it now.  I concur with the 6 turn philosophy as I thought the silly needle valves would fall out after needing to turn them out so much.

so after lots of trial and error and fine tuning, I got it running pretty awesome - EXCEPT.. when I hit the gas to move after being stopped, it hesitates ever so slightly, then wakes up and takes off like I expect.  it's a 1-2 second hesitation that could almost be construed as bogging out, but it recovers quickly and seems fine afterwards.

I'm wondering - I've heard about the 'kick down' solenoid in the transmission to assist with passing.  is that a mechanical linkage that may need adjusting?  could that solenoid be tired and need to be replaced?  is there no such thing and I've been smoking crack again and I should just re-tune til I iron it all out?

Thanks!

-Hank

[Scot Minesinger]

Hankk17,

Sounds like accelerator pump.

You never know with these carbs.  Had to remove my intake manifold and I switched it to an MTS modified stock unit (could never tell it is not original - they smooth intake ports) and so the carb had to be transplanted.  My carb before work was doing the slight hesitation thing, but it was like yours reliable, just a minor thing.  Then after I switched carbs it stopped doing that.

If your intake manifold has ever been off the car, you may have a vacuum leak.

My intake manifold had been off the car before I started working on it and I noticed that it was poorly sealed.  It was well sealed after my work and that smoothed out the idle and made the hesitation go away.  The other weird thing is the idle was completely off and had to be adjusted -no big deal, but thought it would be same as before-not even close.

Sealing is required along entire gasket lip and especially in the corners where the rubber pieces stop, not just around intake ports as stated in directions.  The vacuum from carb communicates with valley pan area through breather/PCV and push rod holes in head.  Needs to be sealed just like at the factory - real well.

[Hankk17]

Well I'm pulling a solid vacuum of 22 inches at idle - nice and steady and no fluttering.  This carb has been rebuilt professionally (Hobbs' carb in NH - did an awesome job).  I put it on last October with the new gaskets the supplied and then torqued it down.  Are you saying to use RTV around the bottom gasket?  I've never done that in the past.  I haven't re-torqued the bolts since I put the newly rebuilt carb on it last fall.  The car's been sitting in the heated garage all winter.. but I hear what you're saying.  I'll check the bolts and will make sure they didn't loosen up.  I'd like to think that Hobbs replaced the accelerator pump with a new one - however, is there anything I can do to ensure it's working as it should aside from vacuum leaks?

Thanks!

-Hank

[DeVille68]

so after lots of trial and error and fine tuning, I got it running pretty awesome - EXCEPT.. when I hit the gas to move after being stopped, it hesitates ever so slightly, then wakes up and takes off like I expect.  it's a 1-2 second hesitation that could almost be construed as bogging out, but it recovers quickly and seems fine afterwards.

I heard from that problem before, the problem was that the secondaries opened too quickly resulting in hesitation. In my 68 Shop Manual there are multiple adjustments involving bending certain levers or taps. Maybe try that?

Regards,
Nicolas

[cadillacmike68]

I don't know if I want toget into this, but here goes:

The stumble upon acceleration is either a lean stumble or a rich stumble. From what you are describing, it's proabaly a rich stumble.

The proper way to  set a Rochester Quadrajet, after verifying that the carb is properly rebuilt with no manifold vacuum leaks is to:

1 Warm up the engine, so that the choke is fully open.
2 Remove And CAP the distributor vacuum advance and the parking brake release hose.
3 Turn the Climate Control OFF.
4 Air Cleaner cover removed.
5 Set Dwell at 30 degrees (if non HEI).
6 Set Ignition timing as per the service manual (usually 5 deg BTDC).
7 Turn Idle speed adjusting screw 1 & 1/2 turns past where it contacts the primary throttle lever.
8 Turn Mixture screws IN until LIGHTLY seated and then OUT 4 turns.
9 Set Idle speed in Drive at 600 RPM (or what your manual says), using the idle speed screw.
10 One at a time, turn idle mixture screws IN until the highest RPM is read, then continue turning IN until a 20RPM lean drop occurs. THEN turn that screw OUT 1 & 1/2 turns. Repeat for the other side.
11 Re-adjust idle speed screw until 600 RPM in Drive, Timing at your manual (probably 5 deg BTDC), Dwell at 30 degrees (no HEI).
12. You're done.

That's the way to set a otherwise properly rebuilt Quadrajet.