Quadrajet stumble... Any suggestions??

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Very well said.
Roy
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wrote:

I had that once... turned out I put the fuel filter in backwards.
Vuarra
Quid quid latine dictum sit altum videtur. (That which is said in Latin sounds profound.)
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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!
Cory
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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. <http://www.chevyasylum.com/tech/carbtool.html 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.
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wrote:

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.
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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.
Cory
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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 look.
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Steve Williams

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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??
Cory

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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 it.
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Steve Williams

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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" intervals.
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.

Your caution is well warranted.
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wrote:

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 Galaxie.
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.
Cory
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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^)

Thexton: <http://www.thexton.com/vshop/shopexd.asp?id 4&catid5> This is a flexible shaft tool for adjusting the idle mixture screws, I used one for many years.
<http://www.thexton.com/vshop/shopexd.asp?id 7&catid5> These are the sockets for servicing all the oddball adjustments on Rochester feedback carburetors. I still use 'em.
<http://www.tooldiscounter.com/ItemDisplay.cfm?lookup=THE370&sourc e=froogle&kw=THE370> 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. <http://members.dandy.net/~k0xp/Oldsmobile/ElectronicQjetPix.htm More stuff can be found at his index: <http://members.dandy.net/~k0xp/Oldsmobile/
Q-Jets and Dual Jets are excellent carburetors -when- set up correctly.
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wrote:

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...
-
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How did it run?
Al 73 Nova, 454 powered:)
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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 shop.....
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Steve Williams



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Caution. Putting a Q-Jet on an adapter is asking for trouble if you use an adapter with an open center. The Q-Jet has a large screw right in the center. If it falls in the engine, KABOOM!
Al
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Thanks for the warning. I plan on using a 4 hole adaptor and massaging it as needed to ensure good airflow thorugh it.
Cory
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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 throttle openings.
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.
Bob...

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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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