Hey, I just got my car going last weekend. Where I first had the timing set it would start up really easy and run pretty good. I messed with it and havent been able to get it quite back to that point. It starts up pretty easy but if I dont give it some gas for the first 30 seconds or so it tries to idle down and it sputters and dies or comes close to dying. How long is the high idle supposed to stay on. Shouldnt it be more than a couple of seconds? What exactly controls this? It is a 350 with a cam, ported heads and lt headers with duals and I havent done any tuning to the carb yet on the primary side but I dont know how much of a difference that will make till it warms up? I have the idle screws at 7 turns out each. This is just where I set them as a starting point because they were both set different. What do I need to do as far as setting these? Do I set this before I set the dwell? I do right? Is there anything else I need to mess with? It seems to run pretty good once warmed up, but is it possible to set the idle a little higher. Is that all the idle screw do or do they change the mixture? Also there are sound files in my sig. Thanks Ben

The high idle is a cam (pivoting weight/lever) on the passenger side of the carb. It is controlled by the thermostatic spring (black round housing on same side), and the choke pull-off (vacuum servo on passenger side front and/or rear of the carb).

If the choke pull-off is adjusted so that it pulls the choke too far open, the high-idle cam will go down too far and cause the idle to go down too much. When the engine is first started cold, the choke should be fully closed. After it starts, the choke butterfly should be opened slightly by the pull-off - but, the high idle won't drop until you tap the throttle, and then it should just drop one notch. As the engine warms up, the electric power to the choke thermostat warms it up and slowly releases the choke until it is fully open when the engine is warm enough to go to closed loop.

The things that can be adjusted are the choke thermostat tension (accomplished by rotating the thermostat towards rich to keep it on longer, or lean to get it to come off sooner), the fast idle speed (separate from the "regular" idle speed set screw), and choke pull-off.

FWIW, the fast idle speed and choke pull-off were the only things (other than "regular" idle speed) I had to adjust after my engine mods.

The mixture adjustments you mention are correct and complete. The idle speed screw does not affect idle mixture.

Thanks for the help. I think I figured out why it wasnt idling as high as it had. I think it was just because my timing was too retarded. I have the style balancer that goes with the timing tab behind the water pump, and dont still have the stock cover on there so I dont have the tab. I would have kept the stock cover from the 305 on this motor accept I thought that the balancer for a 78 would have the old position for the timing mark so I got aftermarket stuff to put the timing mark in the right place. Anyway where I have the timing set it seems to idle about 650-750 now which is about where I want it. I think the reason it went lower is because I didnt tighten the distributer all the way before I took it for a drive. I think that that may have thrown the timing off. Anyway, it still doesnt see to be running high idle right. It seems to kick up to about 1500 rpms and then just drops down a couple seconds later. What adjustment do you think this would be? I dont know that I will even need the high idle with the weather the way it is now, but when it gets cold again(hopefully not until next winter) I want it to be able to run good.

So you didnt set your dwell or anything? I know that the computer will adjust, but wont you get a bit better fuel mileage especially until you hit closed loop if it is set right? With the timing set right, it seems to idle real well, but I would like it to work as effeciently as possible because I have my doubts on how good of mileage I will get anyway and dont want to cheat myself out of more mileage if could be loosing some from not adjusting the carb right. Do you think it will make a difference or not as long as it runs good? I hope to have a scan tool over this weekend to watch for knock and timing and such. If needed, I also will set the dwell and such this weekend. Let me know what you think I need to do and what you think I dont.

Thanks

Ben

It's supposed to do the 1500 RPM for a couple of seconds thing, but it shouldn't be quite that noticeable.

There's a little "kicker" solenoid on the side of the carb that hits the throttle lever. That's what does it, under control of the ECM. Use a ½" wrench and screw the hex plunger in about ½ turn at a time until it does the right thing, which is to hold the idle at about 1400 RPM for about ½ second, just enough to where the throttle doesn't slam shut when you take your foot off the gas and stall the engine. It really is a fine-tuning adjustment, but makes the car much more driveable when set right.

If it's set to too high, the TPS and RPMs will never come down far enough to where the ECM knows it's supposed to drop it out, and the idle will stay up there forever.

It may not have been up there a couple seconds. It may only be 1/2. I will try it again later, but want it to cool down before I try to start it again to see what it does when cool. Anyway, what should the high idle be at. It definately is not staying up at 1500 so that is not a problem, but I dont know that the high idle is working at all if that is a different fucntion. I think I remember seeing that "kicker" but didnt know exactly what it did.

Ben

Hey, I tried restarting it. It was cooled down pretty much but had only sat for maybe 2-2.5 hours. With the timing set right it still started up and ran good, but still no high idle. I did notice that split second jump when I first start it, but it only went to about 1000 not 1400 like you said. Is it supposed to do this every time you start or only when cold. It may not have been cold enough for the high idle so I will try it again tomorrow when it has sat over night. Could someone give me desciptions of what problems will occure if which choke adjustments are off? I am not sure if the high idle is not coming on at all or if it was just coming on a couple seconds like I said. Like I said though I will check again tomorrow when I am sure it is cold.

Ben

Well, I went back to start it today. The first time it started right up and the high idle kicked up to around 1500. It stayed there for a couple of seconds and then started to idle down and died. It did the same thing the second time I tried it. The third time it kicked right up to 1400 and stayed there for about a minute and then the engine light came on. I tapped the gas peddal and it went down to about 900. This third time it seemed to be working like you guys said it should. I then shut it off and checked under the hood to see if I noticed any reason the engine light would have came on. The only thing I found was that the vacuum that goes to the breather assembly was dissconected from the carb. I reconnected it and restarted it. I had no high idle, but had already run for a minute or 2 so that is probably why. It seemed to run good and didnt have the engine light come on. Could this vacuum line have caused my problem or was there another culprit and that was just a coincidence? Also, could that vacuum line have caused my high idle problems? It wouldnt have would it? I will try it again when it cools down since I hooked up the vacuum line to make sure anyway.

Ben

Well, I just went out and tried it agian. There was a little over 2 hours for it to cool with the hood up and everything and I only ran it about 2 minutes earlier. It started ok, but no high idle. It didnt die, but ran a bit shaky at first like it could have used the high idle. I wonder if part of it is just that it is set to cold. That is possible right. I think that the high idle might not be working at to cool of a temp if that makes since. If the motor is warm it shouldnt high idle correct? If it is at high idle(around 1400 rpm) where you would touch the gas to get it to come down, will it eventually idle down on its own or should you have to hit the gas because sometimes it does seem to start up and go to high idle for a couple seconds and then idle down and die. Is this just a choke temp problem, or should you always have to tap the gas for it to idle down?

Thanks

Ben

Well, I just tried letting it warm up and had the air box off of the carb so I coudl watch it. The choke seemed to work fine. It started closed and once it started it cracked. After a minute it opened all the way. Anyway, I also notice that the little vacuum controlled think was blocking out my secondaries even after the motor was at operating temp for a couple minutes. It never let the secondaries open until I turned the car off and there was no vacuum. How do I fix that?

Ben

That's what it's supposed to do.

Think about what happens when you floor the gas. Generally, it had vacuum right before that; when you stomp on it, the vacuum goes away. When that happens, the little diaphragm slowly relaxes, allowing the secondaries to open smoothly. It's a bog preventer.

One of the fine-tuning techniques with a Q-Jet is to drill the orifice a few thousandths at a time until it just begins to bog; then go get a new one, and drill it to where it just barely didn't quite bog yet.

mine does that too.

Does what?