I just rebuilt a 73 Olds Q-Jet, the number is 7043250. It looked to be original, it has 69 Jets, 53c primary rods, CV secondary rods on a K hanger and the stock power valve spring that was in it. A very interesting thing though was that I pulled it off of an engine in an engine pile, so I think it had never been touched, but it has the small holes drilled in the primary butterflys so a large cam can idle. Is this normal? Also, are the jets and rods in the ballpark? '69 Chevelle, 350, Sportsman II heads, Weiand Stealth with 1/2" adapter, 1 5/8" headers, 2 1/2" duals, Comp Xtreme 262 cam; .462/.469 218/224 @.050", 2.73 12 bolt posi, HEI with Jacobs Omni Pak. Currently has a 6210 Holley on it. In Doug Roe's book, he says to drill out the accelerator pump orifices until you have crisp throttle response with no load on the engine. Is this correct? With my heavy car and low gears, I think I'm going to need a big pump shot. Also, does this carb have APT? Many thanks to all the Q-Jet gurus, especially Tommob.

Doug,
The carb might be pretty close. The holes may indicate that it used on a large engine, not necessarily one with a big cam. different divisions handled this stuff different, Chevy tended to use larger idle air bypasses. One method is not superior to the other, mainly just want to get more air in without cranking the throttle open too far.
If you still can, measure the diameter of the power tips of the primary and secondary rods and the length of the sec power tips. Reply here with these and we'll see if it will work.

tommob,

I'll look up the diameters and lengths in a couple of days when the carb and book arrive from home. Would you believe that the airlines won't let you carry a carb in a box as a carryon item!!? http://www.chevelles.com/forum/smile.gif

Doug

P.s. I also have a small selection of hangers and other sec. rods that I pilfered too. I'll look up their diameters then too

[This message has been edited by Doug White (edited 03-15-99).]

tommob,

I got the carb today and as per Doug Roe's book, a 53c primary rod isn't available, but a 52 c is which is a special triple taper 70 olds rod. So, the diameter should be .053"

Secondary rods
I assume power tip is smallest diameter

Top Bottom

CV-.1332-.0527" dia tip length- L 70-100 degrees of air valve opening .25"

CT-.1337-.0774" dia Tip length M 80-100 degrees of air valve opening .125"

CG-.1350-.0774" dia Tip length M .125"

CZ-.1345-.0947" dia Tip length M .25"

Hangers

J, K, L, H

I couldn't get the length of the primary tips, but I have 69 Jets which is .069 dia and .003739277 sq. in.

Any help is greatly appreciated.

Also, can I run the carb without a choke pulloff rod and diaphragm to the secondary air valves?

Thanks.

Doug

Doug, run the CV sec rod in a medium hanger.
On the pri rod, see if you can find a "B" series rod, this fits the early style carb and has a small diameter power tip. 69 and 53 sounds real lean to me, but this carb may have small main air bleeds which richens the whole carb. My current default setup is 73 and 48 which is a lot richer. I normally work on the later style carbs which tend to have larger main air bleeds, so your setup may be equivilant. I'd try to at least round up some bigger jets just in case.

Tom

Doug; This could get long. I am running a simular setup as you and have an Edelbrock O2 sensor installed. Thanks to Tom (tommob) I have been dialing it in and getting pretty darn close. I have had the carb apart 5 or 6 times now and what I am running right now is (primary) no. 70 jets with 39 single taper rods. (sec) DA rods with an H hanger.
The engine runs slightly rich at steady speed, leans out at slight accel., and mid scale at part throttle accel with rods up in about 50 degree weather. The secondaries are real rich now and I am looking at fatter rods to lean it out some if the ignition will fire it ok. I note that the engine will run leaner in cold weather and driving in town with higher underhood temps, it runs richer.
I also took the carb apart and removed the little screw in the baseplate that adjusts the primary metering rod height. I got a screw with the same threads that was about
1 and 1/2 inches long, machined the taper on the end and installed this in place of the original. Now I can easily adjust the mid range with a long standard screwdriver just like adjusting the idle mixture. I did drill out the pump squirters as recommended. The orifice was about .025 to start. I used a Dremel 1/32 in drill bit that gave a .032 sized jet. Could still use more but I'm not sure the pump itself is capable of it. I also went through a couple carbs and found one from a 455 Buick. Had real lean jetting front and rear, but I got lucky and it had a huge gas inlet valve with a new looking Vinton needle. Used to have trouble with lean out in third gear, this took care of that.
Engine is real cold natured now, won't hardly run without choke on cold startup. Used to run with choke unhooked. Getting 23+ MPG and runs better than ever at WOT.
On the choke pull off and rod to upper secondaries butterflies, I've heard that you can adjust the spring tension on these and not use the vacuum dashpot control, but I've always liked the way the four barrel kicks in on a Q-jet just the way they are, so I've never fooled with that. tom
(got pretty long, huh)

OK guys, I need some help here. I installed the Q-JEt this afternoon and after hunting down one vacuum leak on the manifold (a fitting) The car still will not idle at anything less than about 1000 rpm. I know that it has to be the carb because the Holley I just took off idled great, it just had a stumble. What can I look for? Do the holes in the primary butterflys have anything to do with this? Also, the mixture screws don't seem very responsive, but will kill the engine. Dies in gear, except when the idle is set up in park to 1500-1700. engine dies when hand is placed over airhorn too. Any ideas? Will only pull 14-15 inches of vacuum at 900 in park while the holley I just took off of it pulled 18-19 at 900 in park.



[This message has been edited by Doug White (edited 03-20-99).]

Doug,
Sounds like something is way out of whack here. Do you have the right gasket under the carb? Vac leaks are a strong possibility here. There are different gaskets that go between the main body and the baseplate, are you sure you got the right one in there? There are different gaskets between the top plate and the main body, I think you need to check for the correct one. Sounds like you have no idle circuit at all. Certain gasket mismatches can block off the idle circuit between the main body and baseplate. The other popular mismatch involves a massive air leak into the idle circuit at the top plate gasket, either one of these deals will leave you essentially w/o an idle circuit.

I forgot to answer the other Q you asked about the choke pull-off link to the sec air valve. You need this link or you will have terrible bog when the secondaries open. to get rid of the bog you will have to tighten up the air valve spring so tight the spring will be damaged and the air valve will not open all the way. Loser.

Tear down the carb and compare the gaskets you used to the ones that were in there. Look carefully at the area where the idle fuel passes from the main body to the baseplate, see if there's a blockage. The critical area on the top plate gasket is where the idle fuel feed comes up and goes back down the idle well. Looking at the carb as if you were leaning over the radiator to it, this area is at about 7:30 on the drivers side venturi and 4:30 on the passenger side venturi. There is suposed to be a oval shaped hole in the gasket that exposes these two holes to each other. Make sure the gasket doesn't cover up one or the other of the small brass bushings. There are two completely differently shaped areas where the idle well stuff meets the leg out to the booster venturi, check carefully to see that your gasket is correct.

Did you install the two short airhorn/top plate screws that go in under the choke blade right where the pump squirter squirts? They're the ones with heads like a countersunk wood screw.

Check a few of these areas and post your results, we'll figure it out.

Tom (and Tom3 thought his post was long.)

Tommob,

I used a Borg Warner kit and it included the following gaskets.

2 different airhorn/body gaskets

1 thick body to throttle plate gasket.

2 manifold to throttle plate gaskets, one thick with hole stiffeners and one thin.

I carefully compared the two airhorn gaskets, and I am almost positive I installed the correct one, but I guess stranger things have happened.

There was only 1 option for the body to plate gasket. Use the thick one supplied. It matched perfectly to the old one.

Here's where I think I might have screwed up. The two manifold to plate gaskets have slots cut by the primary butterflies, the slots don't match up when the gaskets are stacked together. If the butterfly hole in the gasket was a clock face, and for this example the driver's side hole, the thick gasket has the slot at about 11 o'clock and the thin gasket is at about 7 o'clock. Anyway, I thought I remembered that when I removed the carb from the Olds engine, that it had a thick and a thin gasket stacked together. Also, the thin gasket was more enclosed around the butterflies, like the differene between an open Holley gasket and a 4 hole Holley gasket. So, I stacked the thin atop the thick and in stalled it that way. Am I blocking a passage or anything by having both of these gaskets in there?

I'll play with the gaskets tomorrow and see what I can do.

Thanks for everyone's help and I'll keep you all posted.

Doug, check real careful around those slots you're referring to. The Chevy gaskets don't have those slots. Also, look at the bottom of the baseplate at the sides and rear of the secondaries. There's cavities around there, some GM brands of Q- Jets had vacuum passages in the cavities which will cause problems on a Chevy manifold.

Did the carb have white deposits in the bottom and nooks and crannies where fuel sat and evaporated over long periods of time? When you found the carb, was it situated so that it could be rained in? Expiring minds want to know....

Tom

Doug, you can also try taping over the holes in the pri butterflies with duct tape as a temporary measure to elimate them as a source of problems.

(later) Just noticed another Q I didn't answer. If your power valve piston has a short metal rod sticking out of the bottom, you have APT. From the outside you can usually see a small, flat, round soft plug dead center in the front of the baseplate if the carb's clean. Pop out this plug and there's a little screw deep down in a hole. Turning this screw raises/lowers the power valve, adjusting the part throttle cruise mixture. The screw is often really stuck bad, I've had many that I couldn't free up even with a torch.

Tom

[This message has been edited by tommob (edited 03-20-99).]

Tom3,

I'm really impressed with your direct and innovative approach to fixing the inaccessible APT screw problem. I never thought of that, would never have thought of it. You'll have that thing dialed in so tight it'll squeak. 23MPG, Yeeeessss.

Tom

Yes, the engine was laying on its side in an engine pile. There were some white deposits in the secondary throttle bores down by the butterflys and on part of the secondary butterflys as it must have stood with water in it at some time.

I did my best to clean out all passages. I rebuilt one Q-Jet before, and I know have important it is. It was form a late seventies Olds 88 and it ran really well without any tuning at all (I didn't really know how) I just rebuilt it and slapped it on.

Did I do the correct thing with stacking the base gaskets?



[This message has been edited by Doug White (edited 03-20-99).]

Doug,
re: stacking the base gaskets

I doubt it. If I were you I'd try to find a Chevy 4-hole base gasket and run it. At a parts house, ask for a gasket for a 77 Camaro with a 350 4bbl. If there's vacuum in the cavities on the bottom rear of the baseplate, make sure the gasket covers them.

The reason I asked about the white deposit is that the stuff can build up down in the bottom of the main wells where the idle feed restriction is. I've fixed a number of carbs by having a jobber length 0.038 drill bit. You can use a pin vise to turn this drill, stick it down into the idle feed tube from the top and drill out the orifice at the bottom. Problem is, where to get a jobber length 0.038" drill bit? Regular length bit is too short, won't reach. I'm on my last one and I can't remember where I got the ones I had. I think I had to order them at a tool and die supply house. Handy sometimes, living in a big city....

Tom

GREAT dialog on Q-jet. I printed a copy and will file in my Doug Roe book. Thanks.

------------------
Fred Aldrich
Web Site: www.GeoCities.com/~69_chevelle (http://www.GeoCities.com/~69_chevelle)

here's the debrief on today's events, I better do this while it's still somewhat fresh in my mind.

I took the Q-Jet off the car and removed the airhorn to check for the oval hole for the idle feed. The hole was there and so I removed the base and checked the gasket for all the holes. All the gaskets in the carb check out. I also blew carb cleaner through all of the passages too. All the passages are clean.

I don't have the original gaskets, both because I'm in Maryland now and I rebuilt the carb at home in Missouri over Spring Break. the original airhorn gasket tore when I took the carb apart, but I carefully compared the two included airhorn gaskets. One was not even close and I very carefully checked for all the holes in the one I used.

I went and bought the camaro gasket and used it. It was totally open throughout all the inside of the gasket.

I also replaced the manifold to adapter gasket since I had to remove the adapter to change the bolts in it.

I started it up, it seemed somewhat smoother, but still rough. I'm beginning to think that the throttle shaft bushings are worn out. it has radial play so small you can't see it but you can feel it. It has axial play that you can see, but not much. 1/32" maybe.

It still won't idle below 950-1000, I did finally get it to not die in gear by turning the mixture screws almost all the way out, 4.5-5 turns, but it is still rough and I had to keep it going by blipping the gas.

this carb I think is seriously screwed. I took it out on the road and it took it up to maybe 35 mph and it ran like crap. The car would barely pull itself.

I could get it to idle at 950-1100 and the needle was steady at 18 " below that, it started to shake badly and die.

I didn't tape over the holes in the butterflies. It's not getting enough gas at idle, how can this be fixed?

Once again thanks for all the help.

Let me start by saying this is a very interesting topic on Q-jet tuning.I have worked on Q-jets for fifteen years and I rebuild and modifiy quite a few.I have some questions and some general info to share with you.I have found the throttle rebushing kits that are being sold to work great.I rebushing every carb I rebuild now.I also started glassbeading the complete carb after disassembly.I have not had a bad one yet after starting this.You have to be very careful and blow out every hole with air after your done.I also just purchased a zinc plating and chromating kit from Caswell.I have only plated one carb so far but it looks just like new.Tom did you ever se the kits the Carb Shop sells for modifiying the idle tbe restrictions and the idle channel restrictions?I have bought the kits and used them and they work well.They are expensive but after buying and seeing what they are doing you can make the modifications yourself.I would be glad to send you a copy of the directions,mybe someone could scan them and post them?Is there a book that would tell you what combination of jets and needles where put in a certain carb number.I have a delco book for looking up carb numbers and applications,but it doesn't tell me what jets needles are in a carb.Lastly (for now) anyone know of a electronics wizard that tell us Q-jet tuners how to make a fuel mixture gauge like the one Edebrock and K+N sells.I see they use a comon oxygen sensor.Isn't that just sensing different oxygen content of the exhaust and it changes a voltage reading.Mybe hook it up to a voltmeter would work.Any thoughts or ideas?Well I got to go.

Doug
The way to increase idle fuel is to drill out the idle feed resrictions. But, I don't think this is what is keeping your car from running good on the road at 35MPH. I keep thinking you have a big vacuum leak somewhere, probably around that adapter.

Try taping over the holes in the primary throttle blades. See if this fixes the idle.

Don't worry, we'll get it fixed.

Tom

What did you set the float level at? Should be about 1/4" to 5/16".

VPD--

about the O2 sensor thing, you were right.. you just weld a bung for the sensor right about at your collector and install a good sensor.. a voltmeter should work fine..

i learned of this a while back and have been meaning to do it but alas my exhaust system is one unit if you know what i mean and i cant really remove it w/o removing the motor. but in time i will. in the mean time check out this link that i have provided on my own web page for quite some time.. good info on holleys, and the A:F ratio monitors-

http://home.inreach.com/geewhiz/carb.htm

if you do it let me know how it turns out at michaelr@cts.com thanks

mike reeh

I set the float at 1/4" It will be next weekend before I can continue with troubleshooting this carb. I'm back at the Academy now and locked up for another week. Makes you appreciate your Chevelle more when you can only see her, on the weekends. Thanks for everyone's help.

[This message has been edited by Doug White (edited 03-22-99).]

Tom,

I'm positive the adapter is sealed well to the manifold because I put the 6210 back on it and it idled and ran better than ever. It pulled 19-20" at 950 and was smooth as a baby's butt. Unless there is a leak between the Q and the adapter.

Mike,
Great info on carb tuning.I thnk everyone should take a look at this.I'm going to weld a fitting for an oxygen sensor in my buddie's race car and see how this "do it yourself" air/fuel ratio monitor will work.Thanks again!
VPD

Mike, I agree I can't wait to get this thing welded up and get to playing with it. Thanks for the link.

Doug

Tried to email you acouple times, mail bounced.

"nadn.navy.mil relay refused"

maybe your mailbox is full?

Tom

Doug

Tried to email you acouple times, mail bounced.

"nadn.navy.mil relay refused"

maybe your mailbox is full?

Tom

Tom,

The Navy address should work. m007062@nadn.navy.mil is it. Make sure the m is lower case. If that still doesn't work, e-mail me at gearhead_00@hotmail.com

Look forward to hearing from you soon.

Doug

Just in case, I'll clean out my inbox http://www.chevelles.com/forum/smile.gif
The servers here at the Academy are horrible. http://www.chevelles.com/forum/frown.gif

Doug,
You said the carb came off a 73 OLDS.What kind ok choke does it have?If I remember right all the Olds' used a dial choke that had vacuum going threw a tube down into the intake then back to the choke housing to heat the choke coil.If you are not using the choke make sure you plug the vacuum soure in the choke housing or you will have a vacuum leak that will be hard to find.I agree with Tom about trying to tape the holes in the throttle plates.My general rule of thumb when selecting a Q-jet is to stay with a Q-jet that was made for that engine.(Chevy to Chevy,Olds to Olds,etc).I don't mean find the exact carb number for your application but one thats in the ballpark.That way you don't have that many problems with bolting it on.You don't ave to modifiy the throttle linkage or fuel line or have a problem with a different style choke.You said you engine idles rough and not below 1000 rpm?Carefully look down the primary venturis and see if you can see fuel dripping from the main discharge nozzles at idle.If you do check you power valve to make sure it is closed by seeing if you can push it down by putting a small screw driver threw the bowl vent tube.Just a couple of ideas to check out.I will keep watching to see how you come out.
VPD

Doug,
I just remembered something you can check for.Make sure the secondary throttle plates are closed all the way at idle.Sometime the linkage gets bent this will allow engine vacuum to pull the secondary throttle plates open alittle that creates a vacuum leak.Look at the little tang on the primary throttle shaft some people bend this to make the secondarys open sooner but then it leaves slack in the linkage for the secondarys when the throttle is closed.Look at Doug Roe's book on page 141.This explains it and has
a picture. VPD

VPD,
It has the choke on the housing with a fitting for hot air from steel tube running to the intake. It might have a vacuum passage to it, I'll look. As far as the secondaries, they are tight as a drum and the likage isn't bent.
Being at the Academy, I can't work on it during the week and I have little time on the weekend. A guy I know said he'd look at it for me. He's Sierra Hotel when it comes to Q-Jets. I'll let everyone know what he finds to be wrong with it. Until then, I think I might try to play with that O2 sensor....

Thanks for everyone's help. This site is truly great. My fellow Midshipmen always want me to look at their cars when something goes wrong with them, then they want to know how I learned so much about cars (yeah right)I tell them from reading books and listening to the people who know what they're talking about...you guys are some of these people, Thanks.

BTW, they all think my Chevelle kicks ass and so the muscle car bug has bitten a few of them. Hee HEE.

I'll try to post some pictures of it.

Doug

The fitting where the hot air tube screwed on is a vacuum leak, but not a great big one. Actually, the air that comes thru there is supposed to be accounted for because it pulls air (hot air) through there when it's hooked up on the original car it came off of. Seems to cause trouble when there's nothing hooked up. Best thing: after you get the carb fixed you can plug off the leak with any kind of cap that will fit and install an electric choke from a mid-70's Cadillac. This part has a regular spade terminal and comes off a lot slower than the later ones on smog engines. The later electric chokes had to be off in one minute to meet federal standards, but they made up for it by using the computer to fatten up the mix till the engine warmed up a little.

Tom

Tom,

Does my e-mail work for you now?

Doug