On Thu, 27 Aug 2009 19:59:24 -0700, "Steve Lusardi"
wrote:

The key is low idle vacuum. You have a leak or you have lost index on the balancer and TDC needs to be verified. Don't overlook
the brake vacuum booster, throttle shafts on the carb,PVC valve or EGR valve leakage.
Steve

Don't overlook the vacuum break for the automatic choke either. VERY
common failure point on '60s QJ carbs. If the diaphragm is leaking
you will NOT get it to idle smoothly. PERIOD.

First thing I would do is verify compression. A good leakdown
(aircraft type) tester would be handy as well.
Then VERIFY ignition timing mark (damper) - and if compression is
even but low verify valve timing.
A good ignition scope and someone who knows how to read it can verify
both primary and secondary ignition - I'd put a NEW set of the proper
AC plugs in. With a hot cam, the proper plug will be COLDER than
original. Then check or replace the wires and coil. My preference
would be to put in a later model high energy (electronic) distributor
with the coil built in. and 8mm mag-core wires
Then check ALL vacuum devices for leaks. Block the lines to the heater
controls for testing purposes, and use a "mighty-vac" to check all
diapragms etc. Feed a bit of propane through a hose to all suspected
vac leak areas (throttle shafts, base gaskets, etc that cannot be
verified mechanically..

Unless the replacement cam is "wild" getting it to idle should not be
hard. Getting it to PERFORM can be more difficult.

"oldjag" wrote in message ...
Some metal content, (barely)...This started last spring actually when
I helped a driver in an '69 olds 442 convertable that died on the
roadside. Towed the car to my home garage a block away. Found very
weak spark and traced problem to a made in China, Blue Steak brand
distributor cap that was molded in such a way that the cap pushed on
the breaker points, (actually Blue Streak quality was also bad years
ago before they were made in China). The distributor bearings were
also in dire shape so the dist was replaced. It started and ran well
now, but idled poorly. I checked the air/fuel ratio with a Innovate
wide ratio afr meter and it was lean at idle, about 15-16 afr, and far
too lean for an old car at idle.
The owner had another Quadrajet carb., actually the one that came on
the car, so I rebuilt it, installed a new fuel filter and reinstalled
the carb. Other than the usual stripped inlet filter thread, the carb
looked in good shape. On startup the air fuel was now okay, around
13:1 at idle, and the idle quality was better but still almost
sounding like a miss when listening at the the tailpipes. I checked
for air leaks, brake booster booster, PCV etc. Ran a propane check to
look for leaks around the manifold, compression was 200 psi. on six
cylinders and 180-190 on two others. Idle vacuum was kinda low at 14
inches, at the intial timing of 8 degrees. Everything else looked
okay. The car ran great except at idle, ie it pulled really well at
WOT, chirped the tires when the automatic hit second gear etc., and
lots of torque, but still a lousy idle. The owner was satisfied for a
while, but in the fall decided a engine rebuild was in order. The
engine had 250K plus miles. He asked me if I wanted to do it, but I d
too many irons in the fire. So he took it to a decent local garage
where they yanked the engine for a total rebuild. Two valves appeared
to have been leaking, so intially this was thought probable cause for
the poor idle. Well, here is where it gets weird.
It went off too the machine shop, got hot tanked, got a rebore
0.030" over, stock compression pistons, a 5 angle valve job, new
valve, and valve springs, lifters, cam and main bearings, reground
crank, fuel pump, oil pump, roller timing chain and gears, a new Pro
Comp "mild cam" and a new non points type HEI distributor and wires.
Now get this...it still does not idle right, in fact it's worse and
power is down a quite a bit also. So the garage tries two other
(used) stock Quadrjet and two Holley carbs, still no dice. The cam
timing and ignition timing are checked and rechecked. Compression is
now 220 psi on all eight.
The CompCam is pulled, and an Edlebrock Performer Plus Cam installed.
This is a pretty mild cam, almost stock duration, slightly more lift.
Idle is still crap and vac. won't go over 12 inches unless the timing
is advanced way up. Next the garage pulls the stock intake manifold
and puts on a Edlebrock Performer Plus aluminum intake. No real
change. (A hairline crack was noticed between the secondary bores of
the stock iron intake, but this does not cause an external air leak
and would not effect idle in any case). The exhaust is then dropped
and idle quality does not improve, ie still poor idle vac. The torque
converter is unbolted from the flexplate, idle is still bad, vac.
comes up slightly. Belts are pulled from the fan so no accessories are
running, still no change.

Now the garage wants more money to go further and the owner is livid.
I told the owner to get to an agreement with the shop on who owes what
and bring the car over to let me look at it.
My feeling at this point is that the engine is probably healthy from a
mechanical standpoint, but that the existing Quadrajet Carb.may simply
need to be properly set up for the new cam.

The plan now is to put the stock intake back on and sell the Edlebrock
manifold, as the owner wants a stock looking motor. I don't think the
hairline crack between the secondary bores on the iron stock intake
matters one iota. On many manifolds this area is open anyway. I
could TIG it up, but I guessing this would be a waste of time. None
of the carbs tried may have been jetted right for this engine. Any
Quadrajet/Olds experts out there care to weigh in?