silverriff

So after fixing the vacuum leak on my rebuilt q-jet and not running it for a week or so, I finally got an old engine analizer and a timing gun so I can try my hand at properly tuning it. So yesterday with the help of the 2 top recomended books( the Roe and the other I can't think of) and the service manual, I thought I had everything tuned and ready to go. I even test drove it afterwards and I was very happy. So I woke up today and descided to take it down to my mechanic to have him finetune the mixture and to my dismay when I started my car, the idle speeds seemed to be all screwed up. On first start, it idled at about 2000 rpm. I soon kicked it off to about 1500 rpm. After about 5 minutes of heating up I kicked it again and it slowly dropped to about 1200. It stayed there until I put it in gear then it dropped down to 600. I had set everything according to the tuneup decal and made all the adjustments while following the service manual using the correct gauges...blah blah blah. And everything seemed perfect yesterday. Ugh. So I just decided that it was my first venture into the art of the Q-jet, and I tried, but best to just let my 135 year old mechanic do it, as he can do it with his eyes closed. Any ideas what may be the issue I was running into? I know that's a pretty general question, I am just venting alittle. Oh yeah on top of this, when I was driving to my mechanic, my cheap-*** Grant steeringwheel button flew off so my horn was blowing everytime I turned the wheel slightly. What a day.

RAMBOW

So what happens after the car comes up to operating Temp? does it run the way it did when you set it up?

There is all kinds of factory stuff to make the choke work right- if any of it is missing or messed up it may not work right.

Make sure when you are doing your tuning work you are doing it to a fully warmed up engine.

Another thing of note- Is your engine rebuilt? Most aftermarket camshafts require more inital timing than the factory ones did- this can also affect your performance- but would not cause your idle issues.

I know my 330 runs much better around 16 degrees initial than it did at the 6 degrees the manual calls for.

You can wire your choke OPEN also- and do your tuning and adjustments like that- then unwire it, and get the choke setup.

silverriff

I am not sure about the cam or the rebuild. The 455 was transplanted into it awhile ago. Everything SEEMS stock, but I have never broken it down to find out. Right now I have it set to the initial 8 btdc and with a total of 32 deg. At about 2200 rpm. When the car is at operating temp, it seems to running way too high while it is in park. Where as when I put it in gear, it drops to the 600 rpm I set it at yesterday. I had warmed it up, put the FI cam on the correct step and set it to 1100 rpm per the tuneup decal. But today it seems to be running much higher. Also when I stopped to get gas, after only being turned off for a few minutes, it seems like it had to go through all the "cam" steps again, meaning I had to kick it down 2 times to the normal parked fast idle, which again seemed really high. And it isn't even that cold out today, around 40 deg. or so. About the same temp it was yesterday when it was running very well.

joe_padavano

Yeah, the choke coil is either not adjusted properly or has lost tension. The coil is designed to allow you to adjust the spring tension, and thus rate at which the choke opens (and the idle speed goes down) as the car warms up. This is not a significant problem. You just loosen the three screws holding the black choke coil and turn the coil one way or the other to increase or decrease the opening rate.

firefrost gold

I have a q jet with a electric choke on it . I have not run it yet because when I fired it for the first time i had a vacuum leak from a valley pan to manifold clearance problem( pontiac 400 ) between the intake and the pan i went back to the edelbrock carb because i knew it worked and that s how I knew ( with help from some guys on performance years.com ) that it was a vac leak have not changed back because the air cleaner hit now i have the right air cleaner so I will give it a try long story for me just to say I like the electric choke have had some old fomoco carbs and choke tubes clogged and wouldnt work right . The electric conversion even thought i didnt do it looked easy I got it from sean murphy ind.

joe_padavano

I really prefer the electric choke. This was an option on may Qjets and one of those coils bolts right into the choke housing in place of the standard hot air coil. The "conversion" takes three screws and all of five minutes. Look for mid-80s Chevy trucks with the Q-jet or G-body cars with the V6 and Dualjet carb for choke coil donors.

silverriff

Yeah this qjet has the electro choke and I had adjusted per the chassis service manual...which said to turn it clockwise until the choke "just closes" and then turn it to the apropriate tick on the carb, which for the 72 auto trans was the index tick. I set it to the large center tick and locked it down. It ran really well afterwards, it wasen't until today that it seemed to be running really fast. I don't know, I just need some more practice. But I also need it running because I recently got laid off and am tired of riding the unemployment wave so I need to get out there and start pounding the pavement.

OLD SKL 69

Sounds like you set it up right. It may just be, as Joe said, that the spring has lost it's tension and does not "unwind" all the way so the choke never fully opens up.

silverriff

Well the coil looks brand new just like everything else on the carb. And it is completely open after about 10 minutes of heating up. I don't know, maybe everything is working as it should and I just have the speed or mixture screwed up. Well my mechanic kept it over night so that he can have it good and cold to work on the coil. I will just wait and see what he says and I will report back any solution he comes up with.

silverriff

Alright I got my car back and it seems to be better. The idle mixture definetly seems to be on point. My mechanic doubled checked my "stock" settings and he said the same thing you guys said, that even thought thats what they were supposed to be, on an almost 40 year old engine they may need to be tweeked alittle. Also because of the extremley cold dry air we have had around here for the past few months. So when I got it home I turned the timing up a few degrees and it seemed run a lot better. I didn't have my gun on me but I would estimate around 12 btdc. He also suggested that I change out my vacuum tubing because he thinks I still have a vacuum leak somewhere on the engine that is still messing with my performance. I started closely looking over some of the tubes and some if not all of them look original. The PCV tube is barely being held onto its fittings. Anyway that's going to be the next thing I do is clean up the tubes so they will be one last things that could be causing me issues.