Hi all,
I have a build thread right now, but this question seemed like one that I wanted everyone's opinion on. I just pulled a quadrajet carb off my 1983 305, the engine has a surging problem and supposable it's carb related, obviously the q-jet I have isn't original, and the old owner said it came of a truck, I looked it over, and it looks TIRED! However I want to know what everyone thinks, should I rebuild it assuming the surging problem has nothing to do with the carb, or should I get a new carb. I am thinking about a Summit Racing street or strip carb to replace the q-jet. What kind of performance increase should I see with a new carb, and what kind of cfm should I look for, I saw that I need a em54 q-jet or somthing like that, anyway what do yall think I should do?


Thanks, DacMan

 

I found the #'s on the Q-jet... 17085204 and below that is 2104 HZJ Does anyone know what those mean?. If this is the original I would like to rebuild it, but I don't know how to tell. I'd be more than happy to get pics or more numbers if there are any, just want to decode what this thing is from, and if I can keep it.

 

http://www.carburetion.com/Number/bynumber.asp

http://www.carburetion.com/quadnumber.htm

Looks like an '85 computer q-jet.

 

Hey thanks a lot.
Do you know if this is compatible with a 305. That little number enter site is NEAT!!! I never knew they had those. Looked for em, but couldn't find em'.

Thanks, DacMan

 

It should work fine on a 305.

 

according to the carb doctor, it came off a 305

 

The only reason I ask you fellas if it was compatible was because my engine is surging... I don't know why, and thought maybe that was a sign of the wrong carb or maybe something on the carb was worn. One other thing, today I went and bought a rebuild kit. It came with instructions, but they are **** poor. I went ahead and changes the needle and seat, but I have a bunch of little circle gaskets, small steel *****, and thes little centemeter long shafts... I will post pics later, I have read the intructions and they dont' say what to do with these, should I just leave em' were they are, or figure out what they do and replace em'? Thanks again you guys, I really appreciate your time and effort to help a worthless mechanic.

DacMan

 

Here's a couple good write-ups (1st one should be a sticky)
https://www.thirdgen.org/forums/carb...-ccc-qjet.html
http://www.vetteprojects.com/kstyer/quadrajet.htm

Read em both, keep the pics up on your computer so you can check what you're doing. These should explain where all the parts go. It can be tricky here and there but I'm confident you can do it.

 

Hey thanks man,
Thats' exactly what I need. You're right it should be a sticky.

 

Well boys it's been proven,
A guy can rebuild a Quadrajet and get it to work the first time he's ever done it... well... kinda. Here's my problem, I threw the thing on but it doesn't run quite right. It idles like it's a little lean, and hot. Although on the brite side when I really put my foot into it, it sounds great! But back to idling, it will idle for maybe 30 seconds then die. Let me remind you ofcourse, that I hooked this thing up exactly how it was before. and the guy that had it last wasn't exacltly and ace mechanic, so it could be a combination of it being hooked up wrond and poor adjustment. Any help would be appreciated.

Thanks, DacMan

 

Well I figured why it was dying, my vacuum booster has wiggled off. So back on it went and it idles.. But it idles HOT!!!! So I got to figure out how to make it run more rich, does anyone know how to do this.


Thanks, DacMan

 

Ok everybody, last re-post of the day, lol. Sorry to continually hit this thread but I keep making discoveries. I figured out my problem with the idle odd, I just moved the idle screw in, and now she idles more properly, but there are more problems. First she is still running hot, and I think I know why, the choke flap is fairly open, and I think that's causing her to run lean, it seems like though, that no matter how many times I read it, Ken's description of how to adjust the choke flap is confusing. I don't have a gauge to begin with. I say it's running hot because the exhaust manifold on the drivers side back has this little pipe that sticks up and smoke seems to come out of it, when it idles a while. Not really heavy smoke but some smoke, and it's not colored. Maybe this is normal, I just don't know, so I'm simply guessing it's running hot. Second my secondary flaps won't open, I don't know how much you have to stomp on here to open up, and maybe you really have to, but I give her some serious throttle in shorter bursts and they don' open, it's really confusing. Encluding both of these problems, I am still pretty happy with my carb rebuild, so thanks for the help so far guys, I just need to get it dialed in.

Thanks, DacMan

 

Running lean OR rich will cause it to run hotter than it will at proper mixture, but don't worry about that yet.

The secondary's will only open when the engine is under load-out on the road under power, not in the driveway. You can cleverly position a paperclick so that when the secondary's open it will be displaced, drive and check.

Do we know the timing is good, set properly and advancing correctly?

If you have access to a dwell meter or a scan tool I we can verify the carb is in it's sweet spot of adjustment. Need a volt meter to check/adjust TPS.

The choke blade should be completely shut when cold but once the motor starts up and vacuum is applied to the vacuum break, the break should pull the choke open slightly, maybe 1/4-3/8". I'd have to look up and check those numbers unless someone else chimes in. Usually measured with a drill bit of appropriate size.

 

First of all, Thanks for the helpful ideas. I have no clue about the timing, which I had thought of, I have a light gun and a dwell tac, I just have no clue were the coil is to plug the dwell into, I'll try to find out tonight. As far as the choke flap, it is way the heck to open. That means I want to move the choke spring cover thing counter clockwise a little right? Also I moved the idle screw in and it idles nice now, however I don't know how slow it should idle. I gues I'll wait till I get everything else fixed then work on that. Thanks everyone for the help so far.

, DacMan

 

Alright boys, big news in DacMan's world lol. First of all, I spent thirty minutes looking for my "light gun numbers tab" that you shoot when you time the car. It is not there, am I missing something obvious or am I not looking in the right spot? Now that I have thought about it, it sure runs like the timing is off. Also, here is something really interesting, yesterday morning I noticed my oil level was horribly low, so I decided to change it with some castrol high mileage oil. And then continued to test the car through out the day, lots of starts then run for 3 minutes then stops. Maybe and overall of 30 minutes running time. So here is the cool thing, this oil is supposed to repair and fix old valve seals and other gaskets when used. gimikie I thought, (by the way my car has some not so good valve seals, or so I thought) but today I went to start the car (it had been sitting for about 24 hours) and no, absolutley no smoke came out, wonder why, it always did before, could it be that it was the castrol. I really don't know but if anyone does let me know.


Thanks, DacMan

 

Is there not a tab attached to the timing cover, top driver's side, looking at it through the gap between the balancer and the power steering pump? There should also be a notched line on the balancer that you may need to put some white paint in to make it more easily visible.

Check your timing with the four wire EST connector to the distributor disconnected. The car may not want to idle well with it disconnected and you may have to temporarily bump up the idle speed while you set timing. Do it with the engine warm. Try setting it to four degrees advanced (first big notch on the timing tab after zero). Reconnect everything and re-adjust idle to about 600 rpm. With everything disconnected verify that the timing advances to around 25+ at idle and advances more with throttle. The exact amount isn't as important so long as it is advancing.

Check your TPS voltage by backprobing the three wire connector at the top and middle pins. The connector must be attached to get a reading. The ECM sends 5volt to the TPS on the third lead, one is a ground and the last is the TPS signal lead to the ECM (in case I got the top and middle pins wrong--it's been a while). The TPS should be adjusted so that it reads near 0.40 volts at idle, close is OK. Ensure it reads near 4.0 volts with throttle all the way open. Engine does not need to be running for this test, ignition on/engine off is fine. You may have to drill out the tamper proof plug-be careful. A properly sized roll pin can be lightly tapped over the TPS adjustment screw to turn it.

With timing and TPS set correctly, connect your Dwell meter to the green single wire connector that comes out of the ECM harness near the blower motor. It should be right near the fender where the harness passes through. Other (black) wire to ground. With the engine running and fully warmed up you should see the dwell meter (six cylinder scale) reading near 50% (or 30 degrees) and wavering slightly +/- about 5 or so degrees. The needle will waver as the O2 sensor readings re-write the vac sensor/TPS blocks based on O2. Choking the air horn with a rag should cause the dwell to decrease (less fuel) in response to choking the carb.

If the meter is wavering correctly, adjust the IAB screw to get dwell nearest 50% at idle. Turn out to lean the mixture (get dwell to increase) in to richen mixture (get dwell to decrease). Remember the IAB meters the amount of air that mixes into the air/fuel mixture. Out = more air = leaner. Higher dwell means the metering rods are in the jets more which is a response to a rich mixture (higher dwell = less fuel).

If the dwell reading is steady and unresponsive then the O2 readings are likely out of the narrow range that the sensor can work with (assuming the motor is warmed up and everything else is working correctly). If your readings are steady try shorting out the leads to the Coolant Temp Sensor (CTS). This will trick the ECM into thinking the engine is fully warm and rule out a bad CTS.

Next try setting your idle mixture screws at 2-1/2 turns out each. Run your IAB screw from 2 turns out to 7 turns out, pausing for about a minute each half turn to see if the dwell responds. If nothing go another 1/2 turn on each of the idle mixture screws and repeat. Don't go past 7 turns out on either. The goal is to be near 3-4 turns out on each with dwell near 50% and properly reacting to changes in O2 readings (like choking the air horn).

 

Thanks, May be a while before I get to it, started school today uhhhhhh. But I will let you know what happens, and thanks for your' help.

Thanks, DacMan

 

Hey guys I just realized somthing, I have my dash out so I have been running this thing without a computer . How bad is that? Is that possibly why she's running hot, or had a irratic idle? Just courious.


Thanks, DacMan

 

yes and yes