I got all the parts today. When I rebuild the carb is there a way to test
the solenoid in the carb to ensure it is working correctly before I put it
all back together? What range of resistance should the TPS have from idle to
WOT? Anything else I need to know to ensure the carb is working properly?
To se the timing on this engine do I have to unplug the distributor or
short/jump any pins?
Anything else I should know about this system?
Thanks again to those with helpful input and advice!
12 volts applied to the solenoid connection, the MC plunger
should pull down to its lean stop.
Resistance is meaningless. The correct TPS adjustment is .52
volts at idle setting, it should go to near 5 volts at WOT
(anything above 4.5 volts is acceptable).
You'll need the lean stop measurement gauge to correctly set the
metering rod travel and the double "D" sockets to remove /
replace the MC solenoid and to adjust it (two sizes). Then there
is a different double "D" socket for removing / replacing /
adjusting the idle mixture screws, and a female hex socket for
adjusting the TPS.
mentions a few...
Choke settings are best done with a "choke angle gauge."
(you'll need a mity-vac or some other such vacuum source)
Timing set instructions are on the VECI label, but in general,
Chevrolet carbureted engines were "disconnect the 4 wire
connector" coming out of the distributor.
The MC solenoid duty cycle can be read with a dwell meter set to
the 6 cylinder scale, the dwell meter is connected to the single
"green" connector which breaks out of the electrical harness near
the carburetor and a good ground. You'll want the dwell varying
in between 25* and 35* at idle and at fast idle.
Thanks a lot for all the information. This is exactlyu the type of stuff I
was asking for in the first place. Although I have a general idea how this
stuff works I don't know all the ins and outs of it, and need to get that
information from somewhere. Thanks again, you've been very helpful here.
Aslo ,I think I figured out the MCS works properly... I did teh plugs,wires,
cap and rotor earlier and the car ran poorly afterwards. It idled rough and
smelled pig rich. When I drove it though it ran very strong once I opened
the throttle a bit. Opened the hood again adn saw I forgot to reconnect the
O2 sensor wire on the driver's side. Apparently since it wasn't getting a
signal it defaulted to lean and tried to richen it up to compensate! This
stuff is actually kinda cool.
I took the carb apart and cleaned it up pretty good. It made a world of
difference. The car idles and runs much smoother now and it has more power.
It still bogs when the secondaries come in, but I still have to get that
adjusted right. Even at the same setting though it bogs a lot less and runs
much nicer. I've never seen a carb with so much crud and nasty build-up
inside it, not even old Autolites!
Two questions... The tall screw holding the plate that holds down the MCS...
How much do I tighten that or adjust that to? I set it so there is light
tension on the spring below the screw. It seems to run alright like that,
but I would like to know the correct setting. I counted the turns but I
can't find the apper I wrote it down on (d'oh!).
Also, how do I adjust the TV cable? Aftrer removing it I don't see how to
tighten it. The cable just slides through the part that clips onto the
throttle lever. I figure there must have been a clip on the end or something
but can't find anything. Anyhow, how do I set it properly and how do I
attach it to the throttle lever/clip?
I don't wanna drive it much without getting that TV cable adjusted right. I
know on Ford AOD's if it's way out of whack you can burn up the clutches in
the transmission, so I don't wanna risk that.
TV cable is easy on most later vehicles. The cable end attaches to
either a T stud on the throttle arm on the carb or uses a pin through a
hole. Then you release the cable lock and pull the cable back through
the lock. Get in the car and step on the gas. Go back under the hood and
lock the cable back in place with the clip.
http://www.tciauto.com/instructions/gm_tv_cable_adjust.htm for a quick
"Cory Dunkle" < firstname.lastname@example.org> wrote in message
I adjusted it as per that site. It helped, but there is still a problem...
In overdrive the car 'shudders' a bit when you are lightly accelerating at a
certain point of throttle opening. Give it a little more and it smooths out.
Or put it in drive and there is no problem. What might this be??
Converter going in/out of lock sometimes causes a slight tremor. Might
want to pull the pan and change the filter and fluid in the trans if you
haven't done that yet.
If the fluid is older it could be less lubricating than normal and may
cause stiction in the converter clutch. There is a way to test that by
disconnecting the converter clutch wiring and trying it , just don't run
it a lot like that since it could burn up the clutches in the trans. I
forget which connector it is on that car but a wiring diagram will show
"Cory Dunkle" < email@example.com> wrote in message
That is the lean mixture stop adjustment. To properly set it,
you need the special gauge that fits over one of the main jets,
then the screw is adjusted so that when the metering rod plunger
is pushed down, it -just- touches the gauge.
(This is done without the metering rods installed in the jets.)
Once set, the top is put on the carb and the total metering rod
travel is set by adjusting the rich stop (the larger double "D")
that screws into the carb top. Travel is measured by dropping
the special float level gauge into one of the vent holes either
side of the idle air bleed plunger at the front center of the air
horn, correct metering rod travel is 3/32" - 4/32" lean to rich.
The top end of the rich stop screw is hidden under an aluminum
anti-tamper plug, to remove the plug the rich stop screw is
removed from the carb top with the large double "D" socket, once
out, a pin punch is used to drive the anti-tamper plug out of the
carb top. This allows using the smaller double "D" socket to
adjust the rich stop when the top is back on the carb.
All anti-tamper plugs are then installed where they should be
once the carb is back together and adjusted correctly.
The anti-tamper plugs should not be left out since they hold the
various screws they cover in place and keep them from moving.
(exception being the two idle mixture screw plugs.)
Lacking the correct lean gauge, bottom the screw gently, then
back it out three turns, that should get you close.
Lacking the correct float gauge, fashion your own from a wooden
match stick or soda straw (or similar), by marking it in 1/32"
I make the final adjustments with the carb installed and the
engine running at a fast idle (1800 RPM or so), connect a dwell
meter to the green lead that breaks out of the computer harness
near the carburetor, high dwell means a lean mixture command, low
dwell means a rich mixture command.
If the dwell trends towards 50* adjust both the lean and rich MC
solenoid stop screws -down- in 1/4 turn increments, if the dwell
trends towards 10* adjust the MC solenoid stop screws -up- in
1/4 turn increments. The object is to get the dwell reading
varying between 30 and 35 degrees.
Same goes for idle mixture except that you're going to adjust the
idle mixture screws and the idle air bleed valve at the front of
the air horn.
The original GM training course on this system was three days
long, so you've got your work cut out for you...
The TV cable pulls out as the throttle is opened, it attaches on
the lower side of the throttle lever (make sure you're putting it
in the right place). The adjustment for the TV cable is where
the cable casing bolts down to the manifold or carb, there is
either a metal latch that you depress to release the cable
casing, or a plastic latch that is lifted up to release the cable
casing. Adjust so that when the throttle is at wide open, the TV
cable is at its maximum extension.
Honest to god truth, the TV cable rarely needs adjustment just
because the carb has been removed.
Okay, I got the TV cable adjusted and it works better now. There is one
issue still though. In overdrive right around 34 MPH under light throttle
the car will shudder a bit. Also on the highway sometimes under very light
acceleration it will shudder a bit. Any thoughts? It feels like it may be
the torque converter locking/unlocking real quick. Could it be I don't have
the TV cable adjusted properly?? I read some stuff online that said how to
set it and that was the same as how you said to.
I will make the 3 turns base adjustment to the lean screw in the carb and
check with my dwell meter. Where can I get a tool to adjust the idle mixture
screws while the carb is on the engine? I didn't find any double D
bits/sockets at Advance today when I went for wires/cap/rotor for the
I want to learn these Quadrajets as I want to put an early one on the
Galaxie for better mileage (14-15 MPG with the Holley isn't cutting it). It
seems like the early non-computer Quadrajets should be a heck of a lot
easier. They seem fairly similar to Edelbrocks in some respects.
The TPS (throttle position sensor) has authority over TCC lock
up, it along with the VSS (vehicle speed sensor) are what
determines TCC lock up as long as the various pressure switches
in the transmission valve body are closed.
If you get the same sensation by lightly touching (riding) the
brake pedal and then letting off, it's the TCC engaging.
If you've got a dash mounted tach, you'd see an RPM change when
the TCC cycles on and off.
The mid 80s Chevies didn't have very sophisticated control
stategy, unlike newer stuff where the TCC is applied gradually
via duty cycling the circuit...
Best way to make sure the TCC is applying correctly is to make
sure the TPS voltage is set at curb idle speed. .55 volts.
I wouldn't lie to you... 8^)
This is a flexible shaft tool for adjusting the idle mixture
screws, I used one for many years.
These are the sockets for servicing all the oddball adjustments
on Rochester feedback carburetors. I still use 'em.
This kit has the lean stop gauge, the external float gauge which
also works for measuring MC solenoid travel and the idle air
bleed gauge. The lean stop gauge is not as nice as the OEM
factory issued stuff but it should work fine, the other two tools
look pretty close to OEM factory.
I believe this set has been discontinued by Thexton, if these
guys have it in stock, I'd grab it quick.
<http://www.thexton.com/vshop/shopexd.asp?id 1&catid6 >
Choke angle gauge, only way to get the primary and secondary
choke pull-offs and fast idle cam position set correctly. I used
this one for a few years and then bought one from Snap-On for
much more $$.
It'll work fine for occasional use.
This page has some useful info.
More stuff can be found at his index:
Q-Jets and Dual Jets are excellent carburetors -when- set up
Very true. When set up properly the Qjet can be a great mixer. Very
tunable once you learn the tricks. Nice thing about them is you can set
them up to give great throttle response and great WOT because of the
different sized throttle bores. The main problem was the welch plugs
under the bodies that leaked after a while, pull them clean them and
epoxy and no more leaks. Put a good filter in them and install a heat
shield to keep the carb body cooler. Possibly stack a couple base
gaskets as well to reduce the heat more.
Remember that on the front bores your running a 350-400 CFM carb (better
mileage and throttle response) and when the rear bore tip in you go up
to 750-850 CFM.
Once you figure them out you can play head games with folks at the
track. My favorite car to run was my older Nova with a BB 454 with twin
Q-Jets mounted on a cross ram intake. Fun to drive around town with the
smaller bores doing the work and REAL fun at the track when you stomped
the loud pedal...
Mine was a 69. With a CrowerGlide in it I could get into the mid 10s on
street rubber and pump gas. Gained another half with slicks and good
fuel. Not bad for a street legal toy. I sold it to a guy who put a gas
kit on it and set it up more like a real pro stock car. His second pass
he lost it and went into the rails and destroyed the car. I have a 74
hatchback that I may play with some. Have a nice alloy block in the
----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
The early Quadrajet carburetors were prone to quick wear in the cast iron
base where the throttle plate shafts passed through it. One end had the
bellcrank for the linkages the other a clip retainer. Over time, as pressure
was put on the bellcrank by the linkages to open the throttle plates, it
caused the hole in the base to wear in an oval shape and this caused an idle
mixture that fluctuated engine idle up and down and rpm's at other low
Some manufactures came out with a "nylon sleeved repair kit." This
consisted of two nylon bushings and a few brass washers. The process was to
remove the screws holding the throttle plates in their slots in the throttle
shaft and then removing the shaft itself. After that you drilled a larger
hole as specified THROUGH the existing holes in the base, installed the
throttle shaft back through these nylon bushings and washers and then
reinstalled the throttle plates.
All of this is to tell you to inspect the throttle shaft holes and the fit
for looseness on ANY of these Quadrajets you plan on buying.
Hope this helps. I'm a really old guy who had shops and rebuilt a few of
these a long time ago when they were "new" technology. The technology has
all pretty much passed me now and I am amazed most of the time at the
knowledge and expertise of some of you younger fellows in this newsgroup.
Sounds like my 85 van. Timing and idle were way off. Numerous bad vaccum
hoses. Loose carb screws and bolts. PCV system all clogged up. Replaced PCV
valve adjusted idle set timming new vaccum lines .Runs nice. MPG went from
10 to 16
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