[jims68ragtop]

I had a '70 Firebird 400 engine built up a little, and installed it into my '68 Lemans. I took the old 4-bbl carb from my '68 350 and installed it on the new engine. I do not have an idle stop soleniod (never had one). Yesterday I started it up for the first time. The new engine is running at 1400rpm after being warmed up. I set the Dwell at 30 and the timing at 9 degrees BTDC at the 1400 rpm with the distributor vacuum hose off and plugged. Even with the curb idle screw turned all the way out, the idle rpm stays at 1400.

I don't have a lot of experience with starting up and tuning a newly rebuilt engine. Do I start messing around with the Idle Mixture Screws on the front face of the carb in order to lower the idle RPM's now? The engine is running pretty decent...just too fast.

Thanks.

[Formulabruce]

what year is the carb? 68? Where is your idle mixture screws set at?
ensure your carb is tight and no vacuum leaks..

[jims68ragtop]

Sorry, I don't know what the idle mix screws are set at. How do I determine this? I believe that the carb might be a '68; however, I am not sure. The original Lemans 350 had a 2bbl. Many years ago, I purchased a period correct intake and a reconditioned period correct quadrajet. I now have an Eldebrock aluminum intake with the old carb. The carb is tight. Most of the vacuum tubes had been removed when I bought the car. They are plugged in all places. The 350 ran good with the same set up. I have attached a couple of photos so you can see what I am working with. Thanks.

[Formulabruce]

That sure looks like a 68 pull off.
Ensure the choke plate is open and the HIGH idle screw is adjudted and carb is OFF high idle ( pass side) set the idle mixtures in front to 1 and 1/2 turns open and see how it goes. Sounds like its stuck on high idle though

[jims68ragtop]

Ok, I think I have everything set, but I am not real sure how to make sure it is not set on high idle. I ran the car long enough for the spring in the metal box to pull enough so that the front butterfly valve is straight vertical. I think that means that the carb should set itself to a warm idle rpm. With this set up, the warm idle RPM is stll at 1400. If I continue to turn the idle mix screws outward, will this slow down the idle RPM? In the service manual I found that I should turn the idle mixture screws out four turns. That is where I am right now.

I have not adjusted the fast idle screw at all, because the info that came with the carb said that this adjustment is only for when the engine is cold. It also says not to adjust it unless absolutely necessary.

[Formulabruce]

OK if you have the screws at 4 turns you could turn them in some and see how it runs, make sure its still smooth but as lean as possible ( turning in is leaner)
Look at the metal "cam" the high idle screw is resting against. That has a rod hooked to it that goes up to the choke pull off and indirectly to the choke flapper. That rod must be free and allow that cam to go to the low idle position when motor is warm. That rod and cam often stick when these carbs sit a while.

[jims68ragtop]

Formulabruce, you are a genius! The rod and cam were stuck on the high idle linkages. After getting them to move, things started acting better. However, I am having a hard time lowering the rpms lower than 950 to 1000 without the engine stopping. I know that the factory idle rpms are somewhere around 700 to 800. I am wondering if since I had the engine built up a little (its supposed to be pushing around 400hp) it has to idle at a higher rpm to stay running. It is also in process of being broken in. Your thoughts?

[Formulabruce]

It will idle at 700 unless its got 11 or 12:1 compression.
It seems that there could be a vacuum leak.. either wrong carb base gasket ( very common )
or possibly a leaky vacuum line or cracked vacuum cap
you should have it that high and vary the rpms to 2500 and back for break in, normally.
( this can vary from person to person)
the High idle screw should NOT be touching the choke cam now, if it is you need to back it off as the "low idle" is taken care of on the side near the main throttle arm.
give that a try..
can test for vacuum leaks with starting fluid sprayed around base of carb, or intake manifold

[jims68ragtop]

Ok, I have checked for vacuum leaks, and tightened everything up. I have the idle set up pretty well now. I am finding that the fast idle linkages keep getting stuck. There is a small linkage down where the fast idle screw is located. I think it might be the Primary Throttle Valve linkage according to the service manual. It locks onto the larger linkage which I think is the Cam Follower. I can pull on the cam follower and it easily unsticks. I have lubed this area up and worked it by hand, but when I drive the car, it keeps on sticking. When I pull up to a stop sign, the idle is real high (probably 1600). I can pump the gas pedal, and it will drop back to warm idle. I wonder if I need to do something with the Primary Throttle valve inside the carb?

[Formulabruce]

On a Q jet the choke plate "choke" rod goes inside an area on pass side of carb. It hooks to a cam which has the choke pull off ( indirectly) and the the actual choke stove rod on it.
the rotation point at that cam, needs a bit of cleaning, behind the screw most likely that the cam pivots on. When it wobbles it can cause sticking as well.
If you can pump the gas and idle drops down, you may need to adjust the choke some. you may end up bending the choke rod from the choke stove ( we did this at the dealership, and was GM approved As long as it doesnt hit the choke stove cover.
If your ending idle, after you pump the gas is fine, you have a high Idle/choke problem only..